Far Eastern University – Nicanor Reyes Medical Foundation Physiology B – Vision Experiment (The following results may vary from one group from the other, or from one section to other sections. Please refer to the results of your group and try to see if it matches.) I.) LIGHT REFLEX Function of the Iris: Procedure A: 1. Subject faces the light source covered both eyes with the palm for about 30 seconds. 2. Abruptly remove the palm and observe the pupils. 3. Cover the left eye then observe the pupil on the right. 4. Abruptly remove the cover of the left eye and observe the right pupil. RESULTS After removing cover on both eyes: Both pupils constrict. After covering the left eye: Right pupil slightly dilated. After removing cover of the left eye: Right pupil constricted. Explanation: The pupil constricts when exposed to light because it needs to focus the light rays. Dilated pupils will produce a blurred image since all light enters the eye and stimulates multiple sites. Procedure B: Direct Light Reflex 1. Subject turned away from source of light. 2. Flash light into the eyes and observe the pupil. RESULTS The pupil of the eye flashed with light had its pupil constricted. Procedure C: Consensual Reflex 1. Put cardboard vertically between the two eyes. 2. Flash light on one eye and observe the pupil of the other eye. RESULTS The pupil of the eye not flashed with light was observed to constrict.
Procedure D: 1. Cover the left eye using the palm. 2. With the right eye, look through a pinhole in a piece of cardboard at a uniform white screen for a few seconds. 3. Slightly lift the hand covering the left eye. 4. Observe the size and brightness of the visual field of the right eye. 5. Cover the left eye again, observe. RESULTS Covered left eye: Right eye’s pupil is constricted. After removing the cover of left: Right eye’s pupil goes back or dilates back to normal size. The vision became blurred. Recovering the left eye: Right eye’s pupil constricts. Image becomes clear when left eye is covered. Explanation: When the left eye is covered, the right pupil constricts. The constriction provides a smaller pupil aperture allowing it to concentrate the light more, providing a sharper image. II.) INVERSION OF IMAGE (Projection) Procedure A: 1. Close the eyes and look to the left with eyes still closed. 2. Press the left eyeball on the lateral side, observe. 3. Press the left eyeball on the medial side, observe. 4. Repeat on the right eye. RESULTS Left eye closed, pressed the lateral side: Phosphene ring on medial side of the left eye. Left eye closed, pressed the medial side: Phosphene ring on the lateral side of the left eye. Explanation: Applied pressure on the lateral side stimulates the medial side since the image projected into the retina is inverted, that’s why the other side of the retina is stimulated. It appears as a ring-shaped light since the fingers are semicircular in shape, projecting a ring-like projection in the retina. Procedure B: 1. Make a pinhole on a card or paper 2. Close the left eye and look through the hole via the right eye. 3. Pass a pin across the hole between the card and the eyes. 4. Observe the pin and its shadow. RESULTS If the pin is moved to the right, the shadow is seen going to the left
(Direct Light Reflex) The constriction of the eye flashed with light is due to the connection of the pupil to the Edinger-Westphal Nucleus on the same side via the ciliary ganglion. (Consensual Reflex) The constriction of the pupil of the contralateral eye is due to the afferent limb of the pupillary reflex which is CN2 that has it fibers crossing the pretectal area and reaching the Edinger-Westphal nucleus of the contralateral eye.
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Procedure C: 1. Make 2 pinholes 1mm away from each other. 2. Close the left eye. 3. Look through the two pinholes and observe for the number of pins that you can see when it is placed far and near the cardboard. RESULTS: Two pins were seen when the object was placed far to the hole. One pin was seen when the object was placed near the pinhole.
Explanation: If the object is placed FAR, the light diverges first then becomes parallel; two points will be stimulated, projecting 2 images. If the object is placed NEAR, the light immediately converges stimulating only one part of the retina. III.) VISUAL FIELD Procedure A: Blind Spot
Explanation: Perimeter is used to determine the extent of the visual field of the eye. The eyeballs should have a circular visual field. However, there are barriers that limits the visual field of the eyes: Superiorly: Roof of the Orbit, Forehead, and Glabella. Medially: Nose Inferiorly: Cheek bones The central parts of the results from the perimeter are viewed binocularly, meaning both eyes can see it. The lateral parts of the results from the perimeter are viewed monocularly by the part of the tested eye. However, we do not see two images at once, since the cortex or the center processes and fuses the images sent by the retina. IV.) VISUAL ACUITY
Diagram: The black spot is placed on the medial side of the eye being tested, and the rays are placed going to the lateral side.
1. Place and fix the position of the diagram about 30 centimeters in front of the right eye of the subject. 2. Wrap a sheet of paper in a pencil and leave only the lead tip protruding out. 3. Instruct the subject to fix his gaze on the big dot of the diagram. 4. Place the tip of the pencil in the dot and move slightly across the paper. 5. There will be a point in the diagram where the pencil will not be seen, mark it. 6. Continue until the subject sees the pencil again, mark it. 7. Proceed with the other angles of the diagram. Explanation: Blindspot is due to an area in the eye where the Optic Nerve pierces. Since there are no photoreceptors present in that spot, there will be no image projection. However, we can still see clearly with both eyes, since the blindspot of one eye is seen by the other eye. In the retina, the blindspot is found in nasal side. Due to the inversion of images, in the visual field, the blindspot is found on the temporal side. Use the formula to compute for the size of the retina (not done):
Size of the object Size of the image
Distance from the object to the optical center Distance from image to optical center
Procedure B: Size of Visual Field 1. This procedure uses perimeter to measure the contour and approximate size of the visual field of each eye.
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Right: Snellen’s Test Chart. Left: Astigmatism Wheel Chart.
Procedure: 1. Stand or sit (eye level) at a distance of 20 feet in front of the Snellen’s Test Chart. 2. Cover one eye and test for the visual acuity by asking the subject to read the letters. 3. Also, use the astigmatism wheel chart and ask the patient if he or she sees the line as straight or not. RESULTS: 20/20 vision, no astigmatism. (may vary) V.) COLOR VISION Procedure: 1. We utilized the American Optical Instrument Division Chart and asked the patient to identify the colors using shapes. 2. The test should be finished from the first shape to the last. RESULTS: No color blindness. (may vary) VI.) STEREOSCOPIC / BINOCULAR ACUITY (Results may vary from your computation) Procedure: 1. Place 2 rods (Pencils or Pens may do) 5 cm apart on the table with the other rod (Rod A) placed 30 cm farther back Rod B. 2. Ask the subject to sit in front of the tow rods, 4 m from Rod B. 3. Move Rod A forward until the subject sees the 2 rods appearing to have the same depth or distance. 4. Measure the resolvable distance (Perpendicular distance between the 2 planes occupied by the rods wherein they are perceived to be of the same depth.) 5. Make 3 trials, cover one eye, and repeat the procedure. 6. Do the same procedure, this time the subject is 2 m away from Rod B. 7. Compute using the formula (Please refer to the manual)
Explanation: (from Berne and Levy) Stereopsis is defined as binocular depth perception and appears to be dependent on slight differences in the retinal images formed in the two eyes. Such disparities give different perspectives that lead to visual cues about depth. Stereopsis useful only for relatively near object and depends on the convergent input of the eyes. Stereopsis is useless at distances beyond 50-200 feet. VII.) RETINAL OR TRAIN NYSTAGMUS Procedure: 1. The subject will look at the alternate gray and black vertical lines on the drum. 2. The drum is turned at different speeds. 3. Observe the movement of the subject’s eyes. The subject should also take note his or her perception of the lines.
RESULTS: Results will vary from your computation. What’s important in computing is that: DO NOT DIVIDE THE FRACTION. You need to find the common denominator because the formula for refractive power renders you a whole number: RP = 1 / fd
Procedure B: 1. Place a lens about 30 cm in front of the screen. 2. Also place it 30 cm in front of the object. RESULTS: Image gets sharper Explanation:
RESULTS: When the drum was rotated slowly, there are rapid involuntary movements of the eye. When the drum was rotated fast, the eyes are at a constant gaze. Explanation: Train Nystagmus is a physiologic event where the eyes follow a moving object. However, the rapid involuntary movement of the eyes don’t last for long since the eyes tend to fix its gaze. Pursuit Movement allows the eyes to closely follow a moving object. This is completely voluntary, the patient may decide whether to follow the object or not. Smooth pursuit movement is designed to keep a moving stimulus on the fovea. Train nystagmus have 2 phases: - Slow Phase: When the eyes follow the object. - Fast Phase: When the eyes go back to the midline Slow phase is for Pursuit Movement. Fast Phase is where nystagmus happens and it is for Fixation. The experiment done is an example of a Tortional Nystagmus. VIII.) OPTICS Procedure A:
Procedure C: 1. Put the screen 90cm away from the object and focus it clearly. 2. Move the screen to the object slowly. 3. At about 40cm away from the object, superimpose another lens on the regular lens. RESULTS The image gets blurred. Explanation:
Screen (Represents Retina)
Lens (Biconvex)
Di
Object
Do
Di – Distance of image to nodal point of lens Do – Distance of object to nodal point of lens 1. 2. 3. 4.
Nearsightedness or Myopia can be due to a very long eyeball or a very strong lens. What happens is that the lens converges the light immediately, and the focal point falls in front of the retina. Correction Lens: Biconcave Lens. Biconcave lenses diverges the light first so that when it enters the lens and gets converged, it falls right behind the retina.
Place a screen 50cm away an object. Interpose a lens between the object and the screen. Move the lens until the object appears sharply Compute for the refractive power of the lens (in diopters) using the formula:
1 Do
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1 Di
1 fd
Farsightedness or Hyperopia can be due to a very short eyeball or a very weak lens. What happens is that the lens converges the light late, and the focal point falls behind the retina. Correction Lens: Biconvex Lens. Biconvex lenses will converge the light immediately even before entering the eye, so the image falls in the retina.
IX.) AFTER IMAGES (Results will vary based on what is the color of the object used. ) Procedure A: 1. Fix gaze on a colored object placed against a white background for 15 – 30 seconds. 2. Shift your gaze to a white blank screen or wall. Explanation: You utilize the designated color cone for the designated color of the object. Negative After Image. Upon shifting your gaze on the white background, all color cones are activated, including the first color cones you used for the object. What you will see are the combinations of the unused color cones. The used color cone will function minimally or not at all.
Procedure B: 1. Fix gaze on a colored object placed against a black background for 15-30 seconds. 2. Close your eyes. Explanation: The color used will be the color seen after the eyes are closed. Positive After image. Black Background was used to prevent the stimulation of the other color cones. The image seen when the eyes were closed is the same as that of the object because in dark, no color cones are stimulated except for the first color cone you used to stare at the object before closing the eyes.
“Qridrughyn daor undegon zaldrizes hedry…” (You cannot hide from the sight of my dragons)
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