PERIMETRY Introduction Guide

PERIMETRY Introduction Guide

Perimetry Introduction Guide

Introduction into automated Perimetry using the OCULUS Easyfield, Centerfield 2 or Twinfield 2

Published by: F. Dorner-Schandl Augenklinik Tübingen

Dr. med. B. Wabbels Augenklinik Bonn

Prof. Gerald Kolling

Eike Barczynski

OCULUS Optikgeräte GmbH Muenchholzhaeuser Strasse 29 D-35582 Wetzlar / Dutenhofen GERMANY Phone: +49 (0) 641 20 05-0

FIRST EDITION


Foreword Thank you for the confidence which you have placed in us by your interest for or purchase of an OCULUS perimeter. OCULUS is an ophthalmologic company with a long and proud tradition. For more than 110 years, it has been our goal to produce modern, innovative products which lighten your workload in the routine of daily practice.

We cooperate with many clinics and practicing physicians and develop performance specifications for new instruments in close consultation with them. The introduction guide in front of you will help to become familiar with the new subject. It cannot replace basic education in visual field management but should be useful to refresh knowledge.

OCULUS Optikgeräte Managing director and management team

OCULUS has been certified according to DIN EN ISO 9001:2000 and 13485:2003 and therefore sets high quality standards in the development, production, quality assurance and servicing of its entire product range.

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Content Prefix........................................................................................................................................5 1 Introduction ...................................................................................................................5 1.1 Why using automated Perimetry? ..........................................................................5 1.2 Static or Kinetic Perimetry?....................................................................................5 1.3 The Oculus Perimeters ..........................................................................................6 2 History of Perimetry.......................................................................................................7 2.1 History of Perimetry in General ..............................................................................7 2.2 History of Oculus Perimetry ...................................................................................8 3 Technical Basics .........................................................................................................11 3.1 Luminance ...........................................................................................................11 3.2 The testing grid ....................................................................................................12 3.3 Examination Strategies ........................................................................................16 3.3.1 Threshold-oriented supra-threshold strategy ................................................16 3.3.1.1 Supra Threshold 2-zone............................................................................17 3.3.1.2 Supra-Threshold 3-zone ...........................................................................18 3.3.1.3 Supra Threshold Quantify Defects ............................................................19 3.3.1.4 Class Strategy...........................................................................................20 3.3.2 Threshold strategies .....................................................................................21 3.3.2.1 Full Threshold 4/2 .....................................................................................21 3.3.2.2 Fast Threshold ..........................................................................................22 3.3.2.3 CLIP Strategy............................................................................................24 3.3.3 Kinetic Perimetry...........................................................................................25 3.3.4 Color Perimetry.............................................................................................25 4 Practicing Perimetry ....................................................................................................26 4.1 Examination Advices for Exact Perimetry ............................................................26 4.1.1 General Information ......................................................................................26 4.1.2 General Advices ...........................................................................................26 4.1.3 Long distance correction during the perimetric examination. ........................28 4.2 Selection of Program ...........................................................................................29 4.3 Quality Control .....................................................................................................30 4.3.1 Fixation Control.............................................................................................31 4.3.2 False Positive ...............................................................................................31 4.3.3 False Negative..............................................................................................31 4.3.4 Short Term Fluctuation (SF) .........................................................................31 5 Basic Medical Information ...........................................................................................33 5.1 The Visual Quadrants ..........................................................................................33 5.2 Normal Eye ..........................................................................................................33 5.3 Defects depending on location of the defect in the optic pathway........................37 5.3.1 Prechiasmal defects .....................................................................................38 5.3.2 Defects due to damage to the optic nerve chiasm itself................................41 5.3.3 Defects due to damage posterior to the optic nerve chiasm .........................41 5.4 Defects depending on the location of defect within the visual field ......................42 5.4.1 Depression / Constriction..............................................................................43 5.4.2 Field Cuts / Sector Defects ...........................................................................43 5.4.3 Scotomas......................................................................................................45 6 Glaucoma....................................................................................................................47 6.1 Basic Medical Information on Glaucoma..............................................................47

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6.2 Glaucoma stages according to Aulhorn ...............................................................48 6.3 Examples of Glaucoma Printouts.........................................................................49 7 Further Examples........................................................................................................64 Suffix......................................................................................................................................66 Sources..................................................................................................................................67

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Illustration register Figure 1: Tuebinger Hand Perimeter .......................................................................................8 Figure 2: Tuebinger Automatic Perimter ..................................................................................8 Figure 3: TAP...........................................................................................................................9 Figure 4: Twinfield .................................................................................................................10 Figure 5: Luminance Difference Sensitivity............................................................................11 Figure 6: Goldmann Test Points ............................................................................................12 Figure 7: Example for found scotomas ..................................................................................13 Figure 8: Easyfield Testing Points .........................................................................................14 Figure 9: Glaucoma Test from the Twinfield/ Centerfield .......................................................15 Figure 10: 2-Zone Test-strategy ............................................................................................17 Figure 11: 3-Zone Test-strategy ............................................................................................18 Figure 12: Supra Threshold Quantify Defects stratecy ..........................................................19 Figure 13: Threshold Bracketing Strategy..............................................................................22 Figure 14: Fast Threshold Strategie ......................................................................................23 Figure 15: CLIP Strategy .......................................................................................................24 Figure 16: Exampel picture for using correction lens .............................................................27 Figure 17: Example for Visual field reduction.........................................................................29 Figure 18: Visual Quadrants ..................................................................................................33 Figure 19: Example for an Easyfield measurement printout, healthy eye ..............................35 Figure 20: Example for an Easyfield measurement printout, reduced visual field..................36 Figure 21: Visual pathway......................................................................................................37 Figure 22: Altitudinal defects..................................................................................................38 Figure 23: Optic nerve atrophy ..............................................................................................39 Figure 24: "Curtain" defect.....................................................................................................39 Figure 25: Nerve fiber layers defects .....................................................................................40 Figure 26: Prechiasmal defect caused by swelling of the optic nerve....................................40 Figure 27: Chiasmal damage.................................................................................................41 Figure 28: Posterior damage to the optic nerve .....................................................................42 Figure 29: Left superior incongruous .....................................................................................42 Figure 30: Sector Defects ......................................................................................................43 Figure 31: Sector Defect measured with the OCULUS Easyfield ..........................................44 Figure 32: Relative Scotoma..................................................................................................45 Figure 33: Centro-Cecal scotoma ..........................................................................................45 Figure 34: Para-central scotoma............................................................................................46 Figure 35: Ring scotoma........................................................................................................46 Figure 36: "Seidel´s Scotoma" ...............................................................................................46 Figure 37: Glaucoma stage from:“Rasterperimetrie mit dem Tübinger Automatik Perimeter“48 Figure 38: Illustation fom Oyster, 1999 ..................................................................................49 Figure 39: Glaucoma stage 1.................................................................................................50 Figure 40: Enlarged blind spot ...............................................................................................51 Figure 41: Absolute scotoma caused by a glaucom ..............................................................52 Figure 42: 2 Zone supra threshold strategy ...........................................................................53 Figure 43: Glaucoma stage 2.................................................................................................54 Figure 44: 2 zone supra threshold strategy............................................................................55 Figure 45: Glaucoma stage 3.................................................................................................56 Figure 46: 2 Zone supra threshold strategy ...........................................................................57

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Figure 47: Glaucoma stage 3.................................................................................................58 Figure 48: 2 Zone supra threshold strategy ...........................................................................59 Figure 49: Glaucoma stage 4.................................................................................................60 Figure 50: Glaucoma stage 4.................................................................................................61 Figure 51: Glaucoma stage 5.................................................................................................62 Figure 52: Glaucoma stage 5.................................................................................................63 Figure 53: Enlarge blind spot .................................................................................................64 Figure 54: Hemianopsia.........................................................................................................65

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Prefix This short guide does not intend to replace any professional literature on perimetry. It also cannot be a users manual for Oculus perimeters. It is to be placed right in between these two. It shall explain the Oculus perimeters from a medical point of view. Some parts may look like a guide in perimetry in general. Some parts are identical with the manual. Some parts are completely different from both. However,

1 1.1

Introduction Why using automated Perimetry?

Generally perimetric examinations have three major aims. At first the perimetric reading is helpful for the diagnosis in general. At second they are used for progress monitoring of diseases that affect the visual field. At third they are used in order to judge the visual performance for example at driver´s license tests. When talking about the visual field of one eye, on the first glance it might seem interesting to define the absolute line of

1.2

being able to use a perimeter means to be able to push the correct buttons at the one hand but also means to understand the result of the performed test also. This scripture therefore should provide the link between the manual and medical school. It shall help you to use your perimeter in the way you want to and to read the results and get the information you need from the examination.

vision around the eye. Taking a closer look one will find out that the sensitivity of vision within the complete field is of much more importance. Numerous diseases start in the central 30 degree radius around the fovea. The automated perimeters allow to define the sensitivity on each location up to 90 degree around the fovea, depending on the individual product. Additionally the examination is fast and easy to run and can therefore be done by an assistant too.

Static or Kinetic Perimetry?

There are two general ways to perform automated perimetry, static perimetry and kinetic perimetry. Static perimetry will give the patient a stimulus (in most cases a white light spot) for a short time at a certain position while the patient is directed to look straight ahead at a defined point of fixation. The stimulus is presented in a given size and brightness compared to the background illumination and the patient will respond if

he saw it. By increasing or declining the brightness of the stimulus, the instrument will find out the threshold value as a ratio between the stimulus brightness and background brightness given in dB. As one can see, the measured value is defined by the lowest difference between stimulus and background that the examined person responds to at a certain location. By measuring numerous spots throughout the examined area, a map will develop

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representing the visual field of the tested eye. Kinetic perimetry does not measure the complete area, but the outer line of vision at a certain threshold value. Since the vision decreases with rising distance from the fovea, this method of examination gives lines with a certain threshold value around the fovea, so called isopters, similar to height marks around a

1.3

mountainpeek on a map. The stimulus is illuminated at a certain value outside of the visual field and than slowly moved inwards. The patient will respond as soon as he can see it. After that the procedure starts again, but from a different direction. A regular visual field consists of 4 to 5 isopters and shows the blind spot. The blind spot is found the easiest using a small but bright stimulus, like I/4 according to Goldmann.

The Oculus Perimeters

OCULUS Optikgeraete GmbH, Dutenhofen, Germany produces three different Perimeters: The Easyfield, the Centerfield 2 and the Twinfield 2. The Easyfield is the smallest unit of the three. It offers static perimetry in a 30 degree radius. The test point is white on white background and the test point parameters are corresponding to the Goldmann Standard. The Centerfield 2 offers static perimetry up to 36 degree and using fixation shift even up to 70 degree. Furthermore it offers kinetic perimetry and color perimetry, meaning a blue stimulus is presented on a yellow background. Additionally it offers

the clip strategy. The stimulus brightness and size correspond to the Goldmann Standard as well. The Twinfield is the largest of the three units. It offers static perimetry up to 90 degrees without fixation shift. It offers kinetic perimetry and color perimetry, presenting an either blue stimulus on yellow background or red stimulus. Clip strategy is included. Again, the stimulus corresponds to the Goldmann Standard. The projection system used in Centerfield and Twinfield allows them, to display and reproduce stimuli very exactly, while offering programming features for kinetic perimetry.

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History of Perimetry

Even though one might think that Perimetry is a fairly new subject, it has a rather long history that goes several thousands of years back to the ancient

2.1

Greeks. Here we will try to give you a short overview on the major historical steps and the history of the development at OCULUS.

History of Perimetry in General

Hippokrates (430-380 BC) was the first to be known to get in contact with visual field examination. He diagnosed a vague loss of the visual field as an Hemianopia. Leonardo da Vinci (1452-1519 AD) discovered that the visual field temporally reaches farer than 90 degrees from fixation. From now on the development kept on moving. In 1668 Mariotte found the blind spot. In 1708 Boerhouve defined the scotoma. The word traces back from the greek word skotos, which means darkness. A man called Young was the first to define the outer boundaries of the visual field in 1801 and a man called Purkinje refined Youngs’s work in 1825. Only 31 years later Perimetry had its break through. Von Graefe defined clinical perimetry in 1856. He found sector / curtain defects, enlarged blind spots and central scotoma and classified them.

From now on the development did not stop until today. Since the significance of the visual field was now known, the development of examination methods started. Already one year later, in 1857 Aubert and Foerster developed the first arch-perimeter. In 1945 Goldmann developed the first bowl perimeter and defined standards on the stimulus. That was the final step into the age of visual field examination as we know it today. Parallel, Harms developed perimetric techniques, enforcing his work when he came to Tuebingen, 1952, later supported by Elfriede Aulhorn, while Louise Littig Sloane was working on static perimetry in the U.S.

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2.2


History of Oculus Perimetry

Oculus started to get involved with perimetry about 100 years ago manufacturing a Foerster-perimeter. In 1957 Oculus began to operate more closely with the university eye clinic in Tübingen. The goal was to develop an instrument to examine the visual field. In 1959 the first perimeter was presented and called Tuebinger Hand Perimeter (Picture1). This extremely complex system was built more than 300 times and distributed world wide until 1985. It was the first perimeter that allowed static perimetry and still serves as the underlying principal of almost every automated perimeter on the market today. In 1976 the first Tuebinger Automatic Perimeter was presented at the IPS meeting in Tuebingen (Picture 2).

Figure 1: Tuebinger Hand Perimeter

Figure 2: Tuebinger Automatic Perimter

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Figure 3: TAP

It was followed by the TAP in 1980 at the DOG in Kiel. This was the first OCULUS perimeter that was computer controlled and allowed an examination to run automatically (picture 3). In 1995 Oculus released the Twinfield, the first instrument that allowed computer controlled static and full kinetic perimetry.

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Up to today, the Twinfield sets standards in automated perimetry.

Figure 4: Twinfield

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3 Technical Basics In order to set up the testing conditions needed and choose the right test for each patient it is useful to understand some

3.1

basic technical principals of the used perimeter.

Luminance

The “luminance” is a measurement to describe the reception of brightness which we experience when looking at an object, for example the wall of a room. The typically used measurements to quantify luminance are candela/m² (cd/m²) and Apostilb (asb), while 320 cd/m² equals 1000 asb (cd/m² x π = asb). These two are absolute values, meaning they are comparable with a length in feet or yard, but it is not common to use Apostilb anymore. The relative decibel scale allows to describe any physical value. It gives the deviation to a reference value, which has to be defined. +10 dB will describe a value 10 times as high as the reference value and +20 dB will describe a value 100 times as high as the reference value. The

Figure 5: Luminance Difference Sensitivity

stimulus of the Oculus Easyfield has a reference value of 3180 cd/m² above background illumination, the Centerfield and the Twinfield both have a reference value of 318 cd/m² above background illumination. The background of the three perimeters is homogenously illuminated at 10 cd/m². The result measured in each test spot is the brightness difference between the background and the dimmest stimulus seen by the patient in negative decibel, the so called Luminance Difference Sensitivity (LDS). Therefore, if the patient does not even see the brightest stimulus possible, the value will be zero. The higher the value is, the dimmer is the stimulus, the better is the vision in this certain location. The following figure will show this relation:

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Please note, since these parameters are different for every perimeter, especially for perimeters from different manufacturers, the results are not transferable from one to

another. If exams from different perimeters are supposed to be compared, one has to convert the decibel-values to cd/m²-values above background.

Depending on the perimeter different sizes of stimuli can be used. In the following

figure you can see the luminance and the size of the different Goldmann Test Points:

Figure 6: Goldmann Test Points

3.2 The testing grid Usually it is not a problem to find large, absolute defects, such as complete quadrants or even half-eye defects. One can even find them easily using fingerperimetry. It is much harder to find small and tiny defects. The used grid plays an important role in finding them. The used grid acts like a fishing-net: the denser the grid, the smaller can the defects be that

will be found. But also, the more spots have to be tested and the longer it takes to examine. This might be hard on the patient and also the longer it takes the worse will be the concentration of the patient. Therefore the reliability of the examination might decrease the longer the examination takes.

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Figure 7: Example for found scotomas

Picture 7 illustrates the relation between the number of test locations and the found scotomas. Also, the position of the single spots has to be considered. One important absolute scotoma that has to be found by any grid is the blind spot of the patient. The position of the blind spot is of high importance, as a reference for the doctor. Usually, it will be found at 15° eccentricity, has a diameter of 5° to 6°, 2/3 are below the horizontal meridian and 1/3 is above the horizontal meridian.

Additionally there are several defects which respect the horizontal or vertical meridian, meaning the 0° and 90° axis of the visual field. The only way to find the edges of these defects is by not placing any test spots on both axis. If no spots are on the axis the adjacent spots are close to the axis on each side. Also, on the retina several receptors will be linked to one receptor group. These fields of reception do become smaller towards the centre of the visual field. Therefore the density of the testing spots should be higher in the centre than at the periphery.

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The OCULUS Easyfield has the following grid of test spots:

Figure 8: Easyfield Testing Points

These test spots can be used in any combination. To make the use of the Easyfield more comfortable, it has predefined areas. These areas are based on the standard tests used in automated

perimetry and offer a good compromise between density and testing time for nearly any situation. If not, the perimetrist can define her or his own program. The user manual describes the areas and use.

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The OCULUS Centerfield 2 and Twinfield 2 are built differently and can test any wanted spot within their radius. Thus they are not limited in the amount and locations

of test-spots and can even perform kinetic perimetry. For glaucoma testing the following grid is widely used:

Figure 9: Glaucoma Test from the Twinfield/ Centerfield

The Centerfield and Twinfield also use predefined areas for their testing. But also, they have the option of defining ones own

grid. Again, the manual will guide you through details.

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3.3


Examination Strategies

But not only the brightness and the testing grid are important parameters to the examination. Truly informative perimetric findings are achieved only by presenting test stimuli of different brightness in order to derive conclusions about the threshold of luminance difference sensitivity at each grid location. This procedure is called the "examination strategy".

3.3.1

All Oculus perimeters allow the free combination of strategies with any available grid and to store such combination for repeated use. Moreover, predefined combinations – widely called “program” are installed to make standardized examinations easy, also for the less trained operator.

Threshold-oriented supra-threshold strategy

The threshold-oriented supra-threshold strategy deliberately foregoes exact determination of the luminance difference sensitivity at each location, but it traces it quite closely. With this strategy the presented stimuli are slightly brighter than

expected. The test point must be the brighter the more peripheral the area being examined is located, since luminance difference sensitivity decreases towards the periphery of the retina. This strategy can be implemented in various ways.

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3.3.1.1 Supra Threshold 2-zone (available in Easyfield, Centerfield and Twinfield) The threshold-oriented – supra threshold strategy deliberately avoids an exact determination of the LDS threshold at each point which is examined; rather, it localizes defects by identifying deviations from the normal course of the test during an initial examination. This strategy thus makes it possible to examine many locations in a relatively short time and to reveal small scotomas using a dense fishing-net. A test stimulus of 6 dB brighter than expected is presented (first presentation) at each location which is being examined.

For example: a test point with 27dB is presented if the expected sensitivity is 33dB. The test point is classified as normal (circle) if this test point is recognized by the patient (i.e. the response button was pressed). If the patient does not react to the stimulus, it is again presented with the same brightness. If the patient recognizes it, this location is classified as normal; if not, it is classified as an absolute scotoma (black square).

Start with expected brightness -6dB Respond

Not respond

End Dot OK

Retest same brightness Respond

End Dot OK Figure 10: 2-Zone Test-strategy

Not respond

End abs. loss

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3.3.1.2 Supra-Threshold 3-zone (available in Easyfield, Centerfield and Twinfield) The 3-zone strategy proceeds for the most part in exactly the same way as the 2-zone strategy. - However, if there is no response to the second presentation, the stimulus is again shown with full brightness (0 dB). If

the patient reacts to this test point, it is classified as a relative scotoma (X), otherwise as an absolute scotoma (black square).


Not respond

End Dot OK

Retest same brightness Not respond

Respond

End Dot OK

Retest maximum brightness Respond

End rel. loss Figure 11: 3-Zone Test-strategy

Not respond

End abs. loss

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3.3.1.3 Supra Threshold Quantify Defects (available in Centerfield and Twinfield) This strategy works like the 3-zone strategy. However, if the patient responds to the stimulus when it is presented with maximum brightness, the location is not

only classified as a relative scotoma but the exact threshold value of the scotoma is determined with the help of the 4/2 strategy.


Not respond

End Dot OK

Retest same brightness Not respond

Respond

End Dot OK

Retest maximum brightness Respond

Test exact threshold using the 4/2 strategy Figure 12: Supra Threshold Quantify Defects stratecy

Not respond

End abs. loss

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3.3.1.4 Class Strategy (available in Centerfield and Twinfield) Since of course not every patient has the same degree of sensitivity the Centerfield 2 perimeter is provided with six luminance classes (luminance levels) at 5 dB increments so that it can adapt to different sensitivity levels. The luminance classes of Central threshold luminance measurement TC

Central Selected threshold luminance luminance class measurement at the 15° meridian T15

the Centerfield have been selected according to the average sensitivity level of young persons. Each luminance class corresponds to a collective body of sensitivity values for the anticipated visual field hill.

Symbol

1 30≤TC 22≤T15 25≤TC≤29 17≤T15≤21 2 20≤TC≤24 12≤T15≤16 3 15≤TC≤19 7≤T15≤11 4 10≤TC≤14 2≤T15≤ 6 5 0≤TC≤ 9 0≤T15≤ 1 6 Chart 1: Relationship between threshold luminance in the center or on the 15° circle T15 and the 6 luminance classes

At the start of an examination you have two options: You can either directly select a luminance class on the basis of pre-existing knowledge, as in the case of a follow-up examination, or you can determine the patient's luminance class. There are two automatic methods available for determining the luminance class, both of which essentially consist in determining the threshold as precisely as possible at suitable locations. All the examiner must decide beforehand is whether the macula is intact or whether there may be a disease of the macula. If the macula is intact, the central threshold is determined directly. In this case the computer automatically selects a luminance class that comes closest to the sensitivity level found by the threshold measurement. If a defect is anticipated in the area of the macula, then selection of a luminance class should not be based on the central

threshold. Instead one should measure 4 threshold values at an eccentricity on the 45º and 135º meridians and use the best of these values as a reference for determining the luminance class. Once the luminance class has been defined a program determining LDS at each grid point is executed automatically. First of all the device presents a suprathreshold test stimulus whose luminance is determined by the currently set luminance class and the eccentricity of the point now under study. If the patient recognizes the point, then the examination at that point is already finished. In this case one speaks of the expected sensitivity or, if luminance class 1 has been selected, of normal sensitivity. If the first stimulus is not recognized, the perimeter tests for the presence of an absolute defect by presenting a stimulus of maximum luminance, i.e. 318 cd/m². If this

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is not recognized either, the software classifies an absolute defect at this location. If the patient sees this point of maximum luminance, he may have a relative defect. This is ascertained by presenting the point 3.3.2

with the same brightness as the first time. If the patient fails to recognize the third stimulus, the Centerfield 2 perimeter will then in a fourth step determine the degree of the detected defect and assign it to a luminance class.

Threshold strategies

The threshold strategy determines the threshold value as precisely as possible at each grid location. It must be remembered here that the physiological LDS is not a mathematically precise threshold but rather a transition area between "recognition" and "nonrecognition" of a test stimulus. Within this transition area the probability of recognizing a test stimulus increases or diminishes depending on whether it is presented stronger or weaker. There is thus no "precise" LDS threshold value;

rather, the threshold which is determined with a perimeter must be regarded as having a mall factor of uncertainty. This amounts to 2-3 dB, depending on the eccentricity of the measurement location. A reliable statement about the LDS threshold can be reached only through repeated determination and subsequent appropriate calculation of the mean value. The threshold strategy almost always requires far more presentations for exact measurement of a test point. This should be taken into account when selecting a test grid.

3.3.2.1 Full Threshold 4/2 (available in Easyfield, Centerfield and Twinfield) The "Threshold Bracketing Strategy", as it is also called, determines the threshold value as precisely as possible at each grid location. At the beginning of the examination, as in the supra-strategy, the central threshold is measured in order to arrive at an approximate estimate of the peak of the visual field hill which is to be measured. This procedure yields quite serviceable starting values for the examination. The EASYFIELD Perimeter first extracts 4 points from the selected grid and examines them in isolation, in order to present supra threshold points as rapidly as possible. The patient would promptly tire if a large number of points were to be presented below threshold. Looking at a smaller number of points in isolation has proven to be in-

advisable: the examinee requires a certain readapting interval in order to recognize a point which has been presented first above threshold and then dark again, since the subsequent point is "blanked out" by the previous, brighter point. After completing its examination with these points, the program automatically continues with the next four points. If a point is regarded by itself, the strategy is as follows: The program first presents the point at the expected sensitivity (corresponding to the class). Then the point is "narrowed down" corresponding to the 4 dB / 2 dB strategy. In this Centerfield and Twinfield strategy differs in one aspect from the Easyfield. It extracts five points from the selected grid

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and examines them in isolation, rather than only four.

Start with expected brightness Respond

Not respond

Presentation 4 dB darker

Presentation 4 dB brighter

Respond

Not respond

Not respond

Respond

Presentation 2 dB brighter

Presentation 2 dB darker

Not respond

Respond Respond

Not respond

End

Figure 13: Threshold Bracketing Strategy

3.3.2.2 Fast Threshold (available in Easyfield, Centerfield and Twinfield) This strategy, too, is used to determine the threshold value at each grid location. In contrast to the threshold strategy, four points are not regarded here in isolation, but rather the visual field is examined as a whole. The problem of making presentations "too long below threshold" does not arise with this strategy, since the threshold value which is sought is determined by using a mean value derived in each case from a presentation at

maximum and minimum brightness. - In addition, this strategy uses the results of points already examined in the immediate vicinity of the points currently undergoing examination. The Fast Threshold Strategy is less informative than the Threshold Strategy if the patient's answers are false, but comes to the same results if his cooperation is good, while being considerably faster.

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Search for neighboring points Not found

Found

Starting value with brightness extrapolated from neighboring points

Starting value w ith expected brightness

Presentation of points at initial brightness

Seen

Not seen

Upper bracketing limit = brightness of the corresponding class + 10 dB Lower bracketing limit = Current brightness

Upper bracketing limit = Current brightness Lower bracketing limit = 0

Presentation of point w ith a mean value derived from the lower and upper bracketing limits Not seen

Seen

Upper bracketing limit = current brightness

Lower bracketing limit = current brightness

Discontinue if upper minus lower bracketing limit is less than or equal to 2 dB

End

Figure 14: Fast Threshold Strategie

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3.3.2.3 CLIP Strategy (available in Centerfield and Twinfield) Like the strategies "Threshold" and "Fast Threshold", the CLIP strategy determines the precise threshold value at every point of the test grid. However, the dot is not switched off unless the patient is able to see it. The brightness is continuously increased in steps. Initially one dot per quadrant is pretested to get better start values for the other dots

and to determine the patient´s reaction time. The individual reaction time plays an important role with this strategy. The faster the patient's reaction time is, the faster the brightness can be increased and the faster the examination runs. Measured values which are outside an expected window are automatically retested.

Measurement of central or peripheral threshold, determine reaction time

Pretest 2 dots per quadrant to adapt start values and to correct the peripheral reaction time

Starting value with a class of corresponding brightness

The brightness is increased permanently corresponding to the individual reaction time.

Seen or maximum brightness

Not seen

End of first part

Determine MS value per quadrant Measured value is outside an expected window

Retest dot Figure 15: CLIP Strategy

Value OK

End

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3.3.3 Kinetic Perimetry (available in Centerfield and Twinfield) Kinetic Perimetry is used primarily to define the outer borders of the visual field. But it can be used also, for measuring a complete visual field or to map a scotoma. The stimulus does change neither size nor brightness. It will be illuminated beyond the outer boundaries of the visual field and is slowly moved towards the middle. As soon as the patient sees he will respond. After that, the procedure will be repeated, but from different direction. That way a ring of several positions where the patient will start seeing a stimulus of a certain size and brightness is produced. This ring is called isoptere. After that the brightness will be reduced and the procedure will be repeated. That way one will receive another isoptere, closer to the middle. The completed picture will consist of four to five

isopteres, which define the visual field like height marks define a mountain on a map. Overall this method is a little easier on the patient, and therefore it is advisable to use it for patients who are overchallenged by static strategies or are simply to old. This method is especially useful to measure the peripheral visual field. If a scotoma shall be mapped exactly, this may also be performed with kinetic perimetry. The stimulus is switched on in the middle of the scotoma and slowly moved outwards. As soon as the stimulus is moved out of the damaged area, the patient will see it and reply. This way the outer boundaries of a scotoma can be found very easily. Please see the Twinfield manual for more details.

3.3.4 Color Perimetry (available in Centerfield and Twinfield) Yellow-blue perimetry (SWAP = Short Wavelength Automated Perimetry) is particularly well-suited for detecting juvenile maculopathy and glaucoma patients under the age of ca. 40 years. The problem of blue absorption by the lens

appears frequently in older patients; this makes it difficult to distinguish in the examination results between visual field defects which result from retinal damage and which result from blue absorption by the lens (cataract!).

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4


Practicing Perimetry

4.1 Examination Advices for Exact Perimetry F. Dorner-Schandl, Univ. Augenklinik Tübingen (In thankful memory of my teacher, Prof. Dr. Elfriede Aulhorn)

4.1.1

General Information

The usability and the meaning of a perimetric reading is strongly reduced if consistent examination conditions are not met. Methodical details may vary with the different used instruments, but certain basic rules have to be respected. Important is also to have the same conditions at follow up exams.

4.1.2

The following examination advices are supposed to be clues for inexperienced examiners. Experienced examiners will due to their experience adjust the settings and conditions to the individual visual field and the cooperation of the patient by themselves.

General Advices

In order to run the examination exactly, one has to explain the examination to the patient in simple words. To explain are for instance the fixation control, reply control, opportunities of taking a break and the examination time. Patients have to be motivated and not less important they have to be calmed down if they are nervous and answer all questions about the upcoming examination. This will make the job much easier and increase the cooperation considerably. The patient should sit as comfortable as possible at the perimeter and the correct head-position and fixation has to be kept. Only correct fixation will lead to good results. The better eye is usually examined first. This is important because that way the patient can see the better and is more relaxed when the worse eye is examined.

The eye that is not examined should be covered by an Oculus Occluder. The patient can open both eyes, that way both eyes will have the same adaptation. Some patients are confused by this, which means, that the eye has to be covered with a dark occluder. That might move the threshold values a little. Drops to widen the pupil, ointment or gel should not be given before the visual field examination. Also of influence for the result is the width of the pupil, it is therefore to be noted (the smaller the width of the pupil, the less light will enter the eye). If less light hits the retina, we will receive a reduction of the LDS or the isopteres will be moved inwards a little, which shows more in the middle than in the peripheral field.

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The same effect happens if the opacity of the optical media is higher than normal. Therefore it is important, to consider the pupil widths and the opacity of the media. Using the Twinfield, one has to make sure, that no light from windows or strong lamps shines into the bowl. Also one has to make sure, that there are no shadows in the bowl.

The eye should be moved to the middle of the lens, which can be observed through the monitor. The distance between the eye and the correction lens should be one cm, to avoid scotoma produces by the rim of the lens. If the distance is less, the lens might steam up, which produces relative scotoma. If the distance is to large, artefacts might occur, because the rim of the lens blocks the view of the patient.

Figure 16: Exampel picture for using correction lens

The duration and the frequency of the presentation of the stimulus has to be adjusted to the patient. Especially at the first examination, both eyes have to be tested. The correct lens, according to age and accommodation has to be chosen, just as the correct examination area and strategy.

The examination requires high concentration, therefore the surrounding has to be calm. If the results are not exceptable or no blind spot has been found, the examination has to be repeated completely or in the partial area of interest.

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4.1.3


Long distance correction during the perimetric examination.

It is important, that the stimulus during the visual field examination is displayed very exact, otherwise too low LDS is simulated. Therefore in a case of ametropia a correction lens has to be used, which

complies to the examination standard of 30 cm. An astigmatism of more than 1.0 dioptre should be corrected also.

As standard value, the following is added to the far correction: Age:

0-40 Years: 50-60 Years: 50-60 Years: More than 60 Years:

about +0,5 D. about +1,0 D. about +2,0 D. about +3,0 D.

Individual deviations are possible and have to be considered in each single case. For instance, latent hyperopia at patients between 40 and 50 years need a higher plus correction. For instance:

Spherical and astigmatic lenses can be converted, that way for the best optical illustration the thinner lens can be used.

+4 sph = -3/90° into: +1 sph = +3/0°

(The cylindric lens is added to the sphere, the sign of the cylindric lens is switched and the axis is turned 90°.) The correction should be used during the examination of the areas of the visual field, that show within the glasses, therefore up to about 30° eccentricity. In the peripheral field no correction is needed and only to be kept if the fixation mark cannot be seen at all. Otherwise, scotoma or a concentric visual field reduction at the areas of the rim of the glass can be simulated. Therefore only thin rim corrections lenses are -progression glasses -multifocal glasses -glasses with big rims -toned glasses -absorption edge glasses -half glasses.

allowed, that instrument.

fit

the

holder

of

the

The examination can aslo be done, with the patients full glass near correction glasses, contact lenses or, in the case of good and sufficient accommodation, with the own long distances glasses. To avoid lens rim artifacts due to inadequate correction the following must not be used:

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Figure 17: Example for Visual field reduction

Correction lenses of about -5 dioptre or more, produce a smaller image on the retina and an enlargement of the visual field. The blind spot is a little larger and moved outwards. On a kinetic examination, the isopters are moved outwards also.

Positive correction lenses of about +5 dioptre reduce the visual field, the blind spot is smaller and moved inwards. The isopters of a kinetic examination are moved inwards.

Literature: Rasterperimetrie mit dem Tübinger Automatik Perimeter (F. Dorner-Schandl, W. Durst, G. Kolling, B. Leo-Kottler)

4.2

Selection of Program

We define „ Program “ as the combination of a grid and of a strategy. In Oculusperimeters, several basic programs have been installed to make it easy also for the occasional perimetry-user to find a suitable program for the most common pathologies. Dedicated and experienced perimetrists may want to alter parameters or to create new programs for better adjustment to individual patients needs or less common patterns of scotomas.

There is a basic conflict of objectives in perimetry: You want as much information spatial and in the depth of the possible scotoma. More information requires more examination time, but, the longer this time, the more mistakes will be made by the patient due to the deteriorating concentration. Oculus has worked out grids which are adapted to the physiology of the retina, which helps optimizing the outcome within a given examination time. Other grids are

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made to facilitate comparisons with fields generated at field analysers of other manufacturers (the grids ending with ”-2”).

So there are several questions to consider for the selection or creation of programs:

Strategies are often proprietary of the manufacturers, so it is hard to reach good comparability here. Nevertheless, there are two strategies, which are very common:

At first you should consider the general constitution of the patient. The better, the more extensive examinations you may use.

1. Full Threshold – this is recognized as the most precise strategy, but unfortunately, also the most time consuming. It can be found in most visual field analyzers and thus it is a good one if compatibility with others is important. Remember that the grid combined with this strategy should not have more than approx. 80 locations to test, to limit the examination time to a reasonable level.

Do you want to compare with examinations produced earlier (also at different perimeters)? Use the matching parameters.

2. Suprathreshold (screening) – there are several variations in use (see chapter strategies), so make sure that you use the matching type. Other strategies may be more appropriate for the specific needs of an individual patient. Generally, “Fast threshold” gives reliable values, also CLIP has proved its high reproducibility but needs patients with a reasonable condition and reaction time. In any case, remember that you should stick with the once selected program in order to allow comparison of the patient’s performance over time.

4.3

For Glaucoma and macula suspicious cases, use the programs proposed by the software. For neurological cases a screening strategy with a simple rectangular (-2) grid is sufficient. Do you have a new patient with unclear signs of visual disturbances? A screening over the widest area available can give you a first indication of the critical zone which may then be examined with a threshold strategy. With longer experience, you may wish to make more use of the facilities offered by the open software structure; for the beginning, it is recommended to use the preset programs.

Quality Control

Visual field tests are used not only to retrieve information for itself but also to make decisions about treatment of the patient. Therefore it is essential that we have an idea about the reliability of the results generated by the examination. The clue for this reliability is – apart from a technically stable perimeter – the patient. Monitoring the patient should be done by

the operator, making the patient aware that he/she is not alone, motivating the patient and giving the chance for a break when it becomes obvious that the patient is stressed. Look for attempts to change sitting or head position and for an increasing frequency of blinking.

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Apart from this human factor, which can hardly be replaced by the machine, the perimeters deliver quality control data,

4.3.1 Fixation Control This is probably the most popular method, available in Oculus-perimeters in two different ways.

which are based on three main indices, in most instrument types. In the upper left part of the printouts the quality indices can be found.

surrounding area. Already small deviations of fixation loss will reliably be tracked as the patient will not be able to see the rather dim stimulus.

a) The central fixation control is useful in patients with no macular diseases. It is based on the principle of “false negative”. Before the actual field examination, the instrument determines the level of sensitivity on the macula which has a steep increase of sensitivity in a very small area (approx. 2 degrees) compared to the surrounding area. Within the examination the central stimulus is randomly presented at a brightness just a little higher than the determined threshold but still darker than necessary to be perceived by the

b) The “Heijl-Krakau” method is less sensitive. It is based on the “false positive” principle and uses the blind spot as area where no response is expected. Compared to the macula, the blind spot covers more area and thus allows more deviation from the gazing line before the index alerts the operator. Especially in defects which connect with the blind spot, this method is questionable. However, it should be used when the macula defects are affected.

4.3.2 False Positive Falsely positive response to a stimulus that under regular conditions cannot be seen by the patient or that has not been offered

at all. Thus “trigger-happy” patients can be found.

4.3.3 False Negative Falsely negative response to a previously recognized stimulus. Used in the Oculus

4.3.4 Short Term Fluctuation (SF) At several (usually 10) spots the threshold is determined a second time and compared with the initially derived value. This method – used with threshold strategies only - shows the crux of all the software-based quality control methods: The more presentations you make to get

central fixation control and not shown separately.

clearer quality information the longer the examination takes, BUT: With longer examination, concentration and responsereliability of the patient deteriorate. In other words: If you test SF you will find SF.

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For this reason, modern, fast strategies have reduced the extent of quality control, stressing the importance of close monitoring and motivating by the operator.

It is essential that any deviations from normal fields have to be verified with at least one more examination with at least the same level of precision, before any conclusions concerning possible diseases or treatments are made!

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5

5.1


Basic Medical Information

The Visual Quadrants

Depending on the area of the visual field, different terms are typically used to describe the quadrants of each eye. As one can see from the picture below, the upper part of the visual field of each eye is

called superior and the lower part is called inferior. The part next to the nose is referred to as nasal while the outer parts are called the temporal areas of the visual field.

Figure 18: Visual Quadrants

5.2

Normal Eye

A normal and healthy eye produces a printout as shown in the figure below. The numbers on the top of the page provide some basic information, such as the tested area, the used strategy, the stimulus, the background illumination and so on. As you know each spot on the retina provides perception for the corresponding spot on the opposite side of the visual field. Therefore a stimulus presented on the temporal side of the eye is received by the nasal side of the retina and a stimulus presented on the superior side is received by the inferior side. All printouts show the visual field as the patient sees it. Therefore the optic nerve head, which is nasal, is represented by a blind spot in the temporal side of the visual field.

The grids and maps below provide the actual result of the test. The first grid provides the threshold value in decibel of each tested spot in the retina. The higher the value is, the better is the patients vision in this certain location. Thus a blind spot produces the value “0”. Looking at the location of the optic nerve head, we therefore find the value “0” in our grid. On the right, the result is shown again, but as a map rather than a grid. The lighter the area is coloured, the better is the patients vision. Visual field defects become obvious very easily, e.g. one can immediately identify the blind spot in this picture. In the third grid one can see the deviation from age related norm values. That means, that the patient has an above average perception of the stimulus if a positive value is given and a below average perception if a negative value is given. A

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person who is perfectly within the average would produce a “0” value in each location. One that is above average would produce a positive value in each location. The fourth grid corrects the overall deviation from the average. That way general deviations (such as those produced by a cataract) are disregarded. A person who is above average in each location and produced a + value in each location will produce a grid of “0” values again. A local deviation would show up immediately because it produces strong deviations. At the right hand side of the corrected grid are six single values. The value “MS” refers to the mean sensitivity, the absolute measured mean value. “MD” is the mean deviation. This is the difference between the mean sensitivity of the patient and the age related norm value. “RF” is the reliability factor of the examination. It is produced by the fixation control and the number of false positive replies. The highest possible value is 1.0, but the value should not be below 0.7. “PSD” is the

pattern standard deviation. It shows the deviation of the pattern of the visual field from the age related norm pattern. “SF” shows the short term fluctuation, if it is measured. “CPSD” is the standard deviation for corrected patterns. In this case the PSD-value is corrected by the short term fluctuation. The last two grids will display the calculated P-value. It shows the probability, that the measured threshold is healthy. The second grid is again corrected, to avoid the hiding effect of an overall reduction. The second one of the next two figures will show this very clearly, since in a healthy eye no irregularities are visible in this manner. The “defect curve” gives an image of the overall defect. All points are sorted by value and not by position. Therefore the highest value is entered first, than the second-highest, than the third, and so on. The results of the deviation map are entered. Two (black) lines give the standard range and the red line shows the result of the actual patient.

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Figure 19: Example for an Easyfield measurement printout, healthy eye

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Figure 20: Example for an Easyfield measurement printout, reduced visual field

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5.3


Defects depending on location of the defect in the optic pathway

In order to identify a defect on the grids and maps it is important to have some basic knowledge on the so called visual pathway. Light that is transmitted through the ocular media is first receipted on the retina. As one can see from the below figure an image on the right (1) is received by the retina on the temporal side of the fovea of the left eye (2) and respectively on the nasal side of the fovea of the right eye

(3). It is transmitted by the optic nerve (4) to the chiasm (5) and then on to the left half of the brain (7). The optic nerve is divided into three different parts: The area before the chiasm (4), the chiasm itself (5) and finally the area past the chiasm (6). In the chiasm the nasal nerve fibres cross and the temporal ones change their direction towards the brain.

Figure 21: Visual pathway

The defects showing up on a visual field test can be divided into three groups: 1. Prechiasmal defects: includes any defect in the visual pathway from the cornea to the chiasm. 2. Chiasmal defects: includes defects in the chiasm itself. 3. Postchiasmal defects: includes all defects between the chiasm and the brain. Depending on the location of the defect, different maps are produced by a visual

field test. Therefore the characteristics of the examination result gives hints to where the problem is located. In the following chapter the different characteristics of the three different groups are described. Please note, that the given descriptions are not of any medical meaning. The purpose is simply to point out the relation between some possible defects and the results given by the Oculus field analyzers.

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5.3.1


Prechiasmal defects

These are defects in the visual field caused by a damage to the pathways that are anterior to the optic chiasm, such as a damage to the retina, the cornea or choroids of the optic nerve head for example. These defects are monocular in nature, which means that they can show up in one eye only. Please note, that since a lot of diseases affect both eyes the same defect might show up in both eyes. Therefore, a binocular defect does not necessarily mean that it is not prechiasmal, but a monocular defect means, that it is prechiasmal. Also, altitudinal defects (defects that can be identified as superior of inferior) that are prechiasmal generally respect the

Figure 22: Altitudinal defects

horizontal meridian. This means, that in many cases the defect will not cross the middle line between the upper and the lower part of the visual field. Due to their nature these defects can have various shapes, locations and steepness. The affected area is not necessarily absolutely blind. It can simply have a worse vision than expected. The following pictures will give a short idea. The first example would be macula degeneration, a retinal damage. It will produce a central scotoma like shown in the next figure (right eye: no findings):

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Another example of a disease anterior to the optic chiasm is optic nerve atrophy in one eye, which causes a central field

defect as well as in the left eye (right eye: no finding) of the next figure:

Figure 23: Optic nerve atrophy

he third example to be mentioned can be caused by retinal tears. It creates a so called “curtain” defect, whereby this curtain moves from the bottom to the top. The

Figure 24: "Curtain" defect

picture below shows a typical example. As one can see, the defect shows up in right eye only (left eye: no finding):

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Also monocular in nature are nerve fiber layers defects, caused by glaucoma for instance, as in the left eye in the next

picture (right eye: no finding). Glaucoma themselves are discussed separately in chapter 6 of this brochure:

Figure 25: Nerve fiber layers defects

One other prechiasmal defect is caused by swelling of the optic nerve head due to papilledema or optic nerve head drusen. The static perimetry shows an enlarged

blind spot in either one or both eyes. In the figure below one can see the enlarged blind spot in the right eye (left eye: no finding):

Figure 26: Prechiasmal defect caused by swelling of the optic nerve

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5.3.2


Defects due to damage to the optic nerve chiasm itself

In the optic nerve chiasm the crossing fibers are most vulnerable to damage. As you can see from Figure 22 the nasal fibers from each side cross at the chiasm. Therefore the temporal side of the visual field is most likely to be affected. One common example of a problem causing chiasmal damage is pituitary gland enlargement.

The defect shown in the figure below is called complete bitemporal hemianopsia. It is called bitemporal because the temporal side of both eyes is affected and hemianopsia because the complete half of the eye is affected.

Figure 27: Chiasmal damage

5.3.3

Defects due to damage posterior to the optic nerve chiasm

One typical sign of damages posterior to the optic nerve chiasm is that the field defect is homonymous. This means, that the same side of each eye is affected. As we know from Figure 22, the left part of the visual field of both eyes is received of the right half of the brain and the right part of the visual field of both eyes is receipted of the left half of the brain.

Due to the pathway of the optic nerve, most post-chiasmal defects respect the vertical meridian of both visual fields. The picture below shows an example of a so called right complete homonymous hemianopsia. This defect is often caused by a stroke. The stroke would be in the left part of the brain since the defect is in the right part of the visual field.

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Figure 28: Posterior damage to the optic nerve

The third example of a post-chiasmal defect is a left superior incongruous homonymous quadrantanopia. It means, that the left side of each field is affected, superior refers to the upper half of each field, incongruous because the defects are not exactly the same in each eye,

homonymous because it affects both eyes and quadrantanopia because it affects a quadrant of each eye. As one can see from this example, the fact that post-chiasmal defects are homonymous does not mean, that both defects have exactly the same shape and size.

Figure 29: Left superior incongruous

5.4

Defects depending on the location of defect within the visual field

Visual field defects can not only be described by the location of the cause of the defect, but also by the location and size of the visual field defect. Usually the

visual field defects can be divided into three groups: 1. depression / constriction 2. field cuts / sector defects 3. scotomas

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5.4.1


Depression / Constriction

A depression or constriction is a general reduction of the overall sensitivity of the visual field. The name depends on the testing method. If the visual field was

5.4.2

tested with static perimetry it is called depression. If it was tested with kinetic perimetry it is called constriction.

Field Cuts / Sector Defects

Field Cuts or Sector Defects are defects, that move the outer boundary of the visual field inward. These defects can be caused by retinal detachment for example. Sometimes these defects are also called “curtain defect”. The picture below shows what such a defect can look like. The

Figure 30: Sector Defects

second picture shows an Easyfield printout of such a field cut. The greyscale image makes the “curtain effect” very obvious and the defect curve shows a severe step, typical for defects that make an area completely blind.

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Figure 31: Sector Defect measured with the OCULUS Easyfield

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5.4.3


Scotomas

Scotomas are defects that show up within the boundaries of the visual field. They can have various shapes, positions, steepness and relativity, depending on the cause of the defect. These defects can be described by the terms shallow vs. steep and relative vs. absolute. Additionally they can be described in terms of defect depth. An absolute scotoma is not sensitive to the most bright stimuli available, thus this area is absolutely unsensitive to these stimuli. A relative scotoma is sensitive to brighter stimuli, but not to relatively dim stimuli.

Relative scotomas can be deep or shallow. A deep scotoma is an area in the visual field that is not sensitive to any but the brighter stimuli while a shallow scotoma is sensitive to all stimuli except relatively dim stimuli. The defect depth refers to a value gained from static perimetry. It is a more precise quantitative value to describe the severity of a scotoma. Below you can see an example of a so called central scotoma. It can be caused by macular degeneration, where central fixation is still possible.

Figure 32: Relative Scotoma

The figure 34 shows a common scotoma called centro-cecal scotoma. It extends from the blind spot toward the central vision. This type of scotoma can be caused by an optic nerve lesion.

Figure 33: Centro-Cecal scotoma

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A so called para-central scotoma can be seen in the next picture. It is located around or near the central vision.

Figure 34: Para-central scotoma

A ring scotoma surrounding a normal fovea is called peri-central scotoma. It can be caused by plaquenil toxicity.

Figure 35: Ring scotoma

In the next picture the scotoma has the shape and location of an enlarged blind spot. It is sometimes also called “Seidel’s scotoma”.

Figure 36: "Seidel´s Scotoma"

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6


Glaucoma

Glaucoma are according to Douglas R. Anderson “the most common reason for performing a visual field test in the usual clinical practice.” Even though the scotoma caused by glaucoma are just the 6.1

symptoms of the actual disease, it is inevitably of high importance to examine the visual field. Therefore we will introduce the basics of glaucoma as well as the different stages on the printouts.

Basic Medical Information on Glaucoma

The term “glaucoma” describes several diseases which end up in the same result if not recognized in time: They destroy the optical nerve anterior to the optic chiasm. The most common glaucoma is the so called open angle glaucoma. The majority of all glaucoma patients suffers from this. Slowly, without recognition by the patient, the drainage canals of the chamber water will be clogged. Therefore the water will not drain as fast as it is produced and the inner eye pressure will rise. Eventually the eyeball will start to bend outwards beginning at the weakest spot, the optic nerve head. This will harm the optic nerve fibres, the so called axons, and will produce a decrease or loss of vision in the areas served by the affected axons. Eventually, if no treatment is performed, more and more axons will be damaged and can cause total blindness in the end. Lost vision will not be retrieved through treatment. But a medical treatment is usually assigned to regulate the inner pressure, in order to stop further damage from occurring. Another very common type of glaucoma is the so called normal-tension glaucoma. The optic nerve is harmed, even though the intraocular pressure is not higher than normal. However, the pressure seems to be too high for this particular optic nerve. Angle closure glaucoma, also called acute glaucoma are much more rare than the two above mentioned types. Here a sudden

cause clogs the drainage canals. The inner eye pressure rises suddenly and causes immediate symptoms, such as headache, eye pain, nausea, rainbows around lights at night and blurred vision. The above mentioned types are so called primary glaucoma, because the glaucoma is not caused by any other harm or disease. However, glaucoma can be caused by several other problems. Treatment of the source of the glaucoma will usually stop it from expanding too. The last kind to be mentioned is the glaucoma from birth. In this case the chamber angle has not developed wide enough for the water to drain properly. It needs immediate treatment, but since a baby cannot perform a visual field test it will not be discussed any further in this introduction. If a glaucoma is detected early enough, it can be treated by medication or surgery. As long as there is no severe loss of vision, the eye’s sight can be saved. Unfortunately up to now, lost parts of the patient´s vision can not be retrieved on either way. Therefore it is of high importance to check for glaucoma on a regular basis. Since there is no or only very small loss of vision in the early stage of a glaucoma, follow up is a major part of the saving of the patient´s eye’s sight. Also, the patient will probably not be aware of the development until a very advanced

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stage of glaucoma, because it is a sneaking symptom. Thus, the visual field test is a major factor in the glaucoma

6.2

prevention examination as well as in the follow up.

Glaucoma stages according to Aulhorn

The development of the visual field defect caused by glaucoma was examined and classified by Prof. Dr. E. Aulhorn. Each stage shows typical symptoms within the

visual field. Step by step they show the increasing damage of the optic nerve fibres.

Figure 37: Glaucoma stage from:“Rasterperimetrie mit dem Tübinger Automatik Perimeter“ F. Doner-Schandl, W. Durst, G. Kolling, B. Leo-Kottler, Tübingen, Germany, 1993

Stage 1: relative scotoma according to the affected axons. Stage 2: small absolute scotoma in the Bjerrum region without connection to the blind spot. Stage 3: absolute scotoma in the Bjerrum region with connection to the blind spot, eventually including a nasal step according to Rönne. Stage 4: Further extension of the scotoma into the visual field Stage 5: Collapse of the complete visual field. A small temporal island of vision may remain.

Very typical for glaucoma is the so called “Bjerrum shape” or “Bjerrum region” In the picture below you see an image on how the axons run on the retina. Please keep in mind that you are looking at a two dimensional picture and the actual eye is a ball shape. However, the maps give an idea why the scotoma often appears in an arched shape, the Bjerrum shape.

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Figure 38: Illustation fom Oyster, 1999 http://www.city.ac.uk/optometry/Biolabs/vispath1lab/Visual%20Pathways%20&%20Fields_inprogress.htm

6.3

Examples of Glaucoma Printouts

In the following examples printouts from the different Oculus Perimeters will be given and explained. They will show one example for each stage of Glaucoma. They

are supposed to be a reference for the doctor and also allow one to become familiar with the printouts.

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Figure 39: Glaucoma stage 1

This print shows a relative enlarged blind spot and an archuate relative scotoma inferior to the fovea. Since none of the scotoma is absolute it is a glaucoma stage 1 acc. to Auhlhorn.

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Figure 40: Enlarged blind spot

This visual field also shows an enlarged blind spot. There is a relative scotoma around the blind spot. Another relative scotoma is on the right just below the horizontal meridian.

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Figure 41: Absolute scotoma caused by a glaucom

There is an absolute scotoma right below the fovea and left of the vertical meridian. This one was caused by a glaucoma also, but since the scotoma is already absolute, it is a glaucoma stage 2 acc. to Auhlhorn.

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Figure 42: 2 Zone supra threshold strategy

This shows the same examination as the Figure before, but this time a 2 zone supra threshold strategy is used.

54



This one shows the same situation as in Figure 42. There is an absolute scotoma right below the fovea and left of the vertical meridian. This one was caused by a glaucoma also, but since the scotoma is already absolute, it is a glaucoma stage 2 acc. to Auhlhorn.

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Figure 44: 2 zone supra threshold strategy


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Perimetry Introduction Guide Figure 45: Glaucoma stage 3

This one shows an archuate scotoma, that is absolute in some parts and connected to the blind spot. Since it is caused by glaucoma, it is a glaucoma stage 3 acc. to Aulhorn.

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Perimetry Introduction Guide Figure 46: 2 Zone supra threshold strategy


58


Here one can see a glaucoma stage 3 acc to Aulhorn which already has a nasal Step acc. Roenne. This step is a nasal sector defect, which includes the blind spot.

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Figure 48: 2 Zone supra threshold strategy


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This defect is also caused by glaucoma. Since a larger portion of the visual field is covered by an absolute scotoma, it is considered a glaucoma stage 4 acc. to Aulhorn.

61


Shows also a glaucoma stage 4 acc. Aulhorn. The absolute defect is not as large as in Figure 43, but it already covers a complete quadrant of the visual field.

62


Here you can see an example of glaucoma stage 5 acc. to Aulhorn. The visual field has collapsed completely. A small area of vision has remained in the middle. The threshold of 33 dB in the centre is still acceptable.

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Here is another example of glaucoma stage 5 acc. to Aulhorn. There is almost no more vision left for this eye at all.

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7


Further Examples

In the following chapter you will find further examples of typical examination results. The printouts will look differently, because the examinations are made with different strategies. Please keep in mind, that these

are just examples. In practice the printouts may look different even with the same diagnosis. Anyway they shall help you to become familiar with the printouts.

Figure 53: Enlarge blind spot

Here you see a printout with an enlarged blind spot. It was examined with a supra threshold strategy, therefore it does not give you any threshold values.

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Figure 54: Hemianopsia

This picture shows a hemianopsia. It appears often due to neurological problems, e.g. a stroke. Again, the examination was taken with a supra threshold strategy, therefore no threshold values and no resulting maps and grids are displayed on this printout.

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Suffix

We hope that reading this brochure gave you more of an idea on perimetry in general, how to use the Oculus perimeters and how to understand the results. However, it cannot be the only source of information. We hope you now gained a brief overview and we want to encourage you to keep going in learning and using. However, not even the greatest textbook or the best school can provide every single

piece of information available. Even though we as a manufacturer try to provide you with every information you might need, eventually you will lack a piece earlier or later. In this situation we and our distributors will be glad to answer your phone-call or e-mail. In this means we hope that you will appreciate working with your instrument and the multiple possibilities it offers you.

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Sources

Rasterperimetrie mit dem Tübinger Automatikperimeter, Dorner-Schandl, A. et al. Eigenverlag, Tübingen/Heidelberg 1993 Perimetrie, Lachenmayr, B., Vivell, P.M.O.: Thieme, Stuttgart 1992 Early visual field defects in glaucoma, Aulhorn E, Harms M., Leydhecker W (ed). Glaucoma, Tutzing Symposium, pp 151-186, Basel, Karger. 1967 Automated Static Perimetry, Douglas R. Anderson, M.D., St. Louis, USA, 1992 Atlas der Computer Perimetrie, Jörg Weber, V. Verlag, Berlin, 1993 www.eyetec.net - Module 11 - The Visual Pathways and Visual Field Defects

PERIMETRY Introduction Guide

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