PHYSIOL 404 EXAM 1 UPDATED ACTUAL QUESTIONS
AND CORRECT ANSWERS
Question:
1. Blind spot- methods
Answer:
- An X was drawn on the right side of the paper, while a dot was drawn on the right side
- Cover left eye and look at dot until it seems to be invisible. This is the blind spot
- Repeat for right eye
Question:
2. Blind spot- results
Answer:
Dot disappeared several inches from paper on same side as covered eye
Question:
3. Blind spot- discussion Why is there a blind spot in the visual field of each eye?
Answer:
The optic disc is where the nerves and blood vessels of the eye exit and it contains no receptors when
focusing an image there, it appears invisible.
Question:
4. Blind spot- discussion Why is the blind spot temporal to the object of focus in the visual field, but nasal
to the fovea on the retina?
Answer:
When experiencing the blind spot, the object will be in the temporal visual field even though the blind spot
is in nasal because light travels in straight lines.
Question:
5. Visual acuitymethods
Answer:
The participant was asked to cover one eye and read the letters on the lowest line that was comfortable.
The same task was repeated while covering the opposite eye. The charts are viewed at a distance of 20 feet,
and visual acuity is represented as a ratio in which 20/20 indicates perfect vision.
Question:
6. Visual acuity- results
Answer:
A participant with 20/25 vision means that someone with normal vision could see the smallest letters read
by the participant at a distance of 25 feet, rather than 20 feet as was completed by the participant.
Therefore, the left eye has a lower visual acuity compared to the right eye, indicating possible myopia or
astigmatism.
Question:
7. Visual acuity - discussion Be able to determine relative visual acuity based on Snellen results
,Answer:
Visual Acuity = Actual testing distance (20 feet) / Distance at which the smallest letters can be read by a
subject with normal vision
Question:
8. Visual acuity - discussion Know what the numerator and denominator of the Snellen results signify
Answer:
The numerator indicates the distance (in feet) from the chart which the subject can read the line. The
denominator indicates the distance at which a normal eye can read the line i.e. 20/40 vision, 20/15 vision
Question:
9. Convergence of gaze- methods
Answer:
In this experiment, we looked at convergence of gaze, which describes the inward turn of the eyes when
looking at a close object (as demonstrated when the subject focused on an object 7-10 inches from their
face). Next, the subject held their hand up 7-10 inches from their face with the index finger aligned with a
distant fixed object; while focusing on the finger, they covered their right eye. Finally, the subject opened
both eyes to focus on the distant object; then they maintained focus on the distant object and covered their
right eye.
Question:
10. Convergence of gaze- results
Answer:
When shifting focus from a distant to a close object, the subject's eyes turned inward. When focusing on
the close object (index finger), the subject noted that there were two images of the distant object (a water
bottle) and that the right temporal image of the bottle disappeared when the right eye was covered. When
focusing on the distant object, the subject noted that there were two images of the close object, and that the
left nasal image of the finger disappeared when the right eye was covered.
Question:
11. Convergence of gaze-discussion Be able to explain the reason behind the physiological diplopia
observed (in terms of the specific parts of the retina that are responding to light from the near and far
objects).
Answer:
Because the close image is nasal, the image hits the retina at the temporal region (where the fovea is)
because light travels in a straight line. This causes double vision, or diplopia, of the background image
since it is no longer focused on the same part of the retina in each eye like the close image is.
Question:
12. Convergence of gaze-discussion Know the basic organization of the visual field map and how it
corresponds to the retinal map of the eyes.
Answer:
Something on the right visual field hits temporal in left, nasal in right and vice versa
Question:
13. Positive Afterimages- methods
, Answer:
Positive:
-Turn on the flashlight on your cell phone.
-Close both eyes and cover them with your hands. Wait for 10 seconds.
-With a helper pointing the flashlight at your closed eyes, remove your hands, and open your eyes for the
shortest possible time, then close them again.-Note the afterimage. Bright features of the scene remain
visible for an appreciable time (a substantial fraction of a second).
Question:
14. Positive Afterimages- results
Answer:
Bright white spot was visible
Question:
15. Positive Afterimages- discussion Know what is happening at the level of the involved photoreceptors
to result in this phenomenon (i.e., an image of similar color to the originally observed stimulus persists
even after the stimulus is removed). Your discussion should include an overview of the process of
photoisomerization, as well as the prolonged hyperpolarization that results from photoreceptors stimulated
with bright light (photobleaching).
Answer:
Our eyes are able to transduce light into electrical signals that can be interpreted by our brain.
Photoreceptor cells contain opsins and retinal; cis-retinal is unstable and exists in the dark, covalently
bound to the opsin. When cis-retinal absorbs a photon of light, it isomerizes to trans-retinal and initiates a
series of changes that result in hyperpolarization of the photoreceptor membrane: trans-retinal and opsin
dissociate (photobleaching), opsin activates transducin, transducin activates phosphodiesterase (PDE),
PDE hydrolyzes cGMP to GMP, and the decrease in cGMP levels closes cation channels and thus results
in hyperpolarization of the membrane and a graded decrease in neurotransmitter release. The brighter the
light, the more time it will take for the opsin and retinal to recuperate and be able to respond properly to a
new stimulus
Question:
16. Negative Afterimages- methods
Answer:
-Stare at the red square image below for 30 seconds. You may blink but should take care to keep your gaze
fixed.
-Shift your gaze to a piece of plain white paper and note the after-image. The image lasts for many
seconds. The image is inverted in contrast, hence the name 'negative afterimage'.
Question:
17. Negative Afterimages- results
Answer:
I saw a blue/yellow colored image
AND CORRECT ANSWERS
Question:
1. Blind spot- methods
Answer:
- An X was drawn on the right side of the paper, while a dot was drawn on the right side
- Cover left eye and look at dot until it seems to be invisible. This is the blind spot
- Repeat for right eye
Question:
2. Blind spot- results
Answer:
Dot disappeared several inches from paper on same side as covered eye
Question:
3. Blind spot- discussion Why is there a blind spot in the visual field of each eye?
Answer:
The optic disc is where the nerves and blood vessels of the eye exit and it contains no receptors when
focusing an image there, it appears invisible.
Question:
4. Blind spot- discussion Why is the blind spot temporal to the object of focus in the visual field, but nasal
to the fovea on the retina?
Answer:
When experiencing the blind spot, the object will be in the temporal visual field even though the blind spot
is in nasal because light travels in straight lines.
Question:
5. Visual acuitymethods
Answer:
The participant was asked to cover one eye and read the letters on the lowest line that was comfortable.
The same task was repeated while covering the opposite eye. The charts are viewed at a distance of 20 feet,
and visual acuity is represented as a ratio in which 20/20 indicates perfect vision.
Question:
6. Visual acuity- results
Answer:
A participant with 20/25 vision means that someone with normal vision could see the smallest letters read
by the participant at a distance of 25 feet, rather than 20 feet as was completed by the participant.
Therefore, the left eye has a lower visual acuity compared to the right eye, indicating possible myopia or
astigmatism.
Question:
7. Visual acuity - discussion Be able to determine relative visual acuity based on Snellen results
,Answer:
Visual Acuity = Actual testing distance (20 feet) / Distance at which the smallest letters can be read by a
subject with normal vision
Question:
8. Visual acuity - discussion Know what the numerator and denominator of the Snellen results signify
Answer:
The numerator indicates the distance (in feet) from the chart which the subject can read the line. The
denominator indicates the distance at which a normal eye can read the line i.e. 20/40 vision, 20/15 vision
Question:
9. Convergence of gaze- methods
Answer:
In this experiment, we looked at convergence of gaze, which describes the inward turn of the eyes when
looking at a close object (as demonstrated when the subject focused on an object 7-10 inches from their
face). Next, the subject held their hand up 7-10 inches from their face with the index finger aligned with a
distant fixed object; while focusing on the finger, they covered their right eye. Finally, the subject opened
both eyes to focus on the distant object; then they maintained focus on the distant object and covered their
right eye.
Question:
10. Convergence of gaze- results
Answer:
When shifting focus from a distant to a close object, the subject's eyes turned inward. When focusing on
the close object (index finger), the subject noted that there were two images of the distant object (a water
bottle) and that the right temporal image of the bottle disappeared when the right eye was covered. When
focusing on the distant object, the subject noted that there were two images of the close object, and that the
left nasal image of the finger disappeared when the right eye was covered.
Question:
11. Convergence of gaze-discussion Be able to explain the reason behind the physiological diplopia
observed (in terms of the specific parts of the retina that are responding to light from the near and far
objects).
Answer:
Because the close image is nasal, the image hits the retina at the temporal region (where the fovea is)
because light travels in a straight line. This causes double vision, or diplopia, of the background image
since it is no longer focused on the same part of the retina in each eye like the close image is.
Question:
12. Convergence of gaze-discussion Know the basic organization of the visual field map and how it
corresponds to the retinal map of the eyes.
Answer:
Something on the right visual field hits temporal in left, nasal in right and vice versa
Question:
13. Positive Afterimages- methods
, Answer:
Positive:
-Turn on the flashlight on your cell phone.
-Close both eyes and cover them with your hands. Wait for 10 seconds.
-With a helper pointing the flashlight at your closed eyes, remove your hands, and open your eyes for the
shortest possible time, then close them again.-Note the afterimage. Bright features of the scene remain
visible for an appreciable time (a substantial fraction of a second).
Question:
14. Positive Afterimages- results
Answer:
Bright white spot was visible
Question:
15. Positive Afterimages- discussion Know what is happening at the level of the involved photoreceptors
to result in this phenomenon (i.e., an image of similar color to the originally observed stimulus persists
even after the stimulus is removed). Your discussion should include an overview of the process of
photoisomerization, as well as the prolonged hyperpolarization that results from photoreceptors stimulated
with bright light (photobleaching).
Answer:
Our eyes are able to transduce light into electrical signals that can be interpreted by our brain.
Photoreceptor cells contain opsins and retinal; cis-retinal is unstable and exists in the dark, covalently
bound to the opsin. When cis-retinal absorbs a photon of light, it isomerizes to trans-retinal and initiates a
series of changes that result in hyperpolarization of the photoreceptor membrane: trans-retinal and opsin
dissociate (photobleaching), opsin activates transducin, transducin activates phosphodiesterase (PDE),
PDE hydrolyzes cGMP to GMP, and the decrease in cGMP levels closes cation channels and thus results
in hyperpolarization of the membrane and a graded decrease in neurotransmitter release. The brighter the
light, the more time it will take for the opsin and retinal to recuperate and be able to respond properly to a
new stimulus
Question:
16. Negative Afterimages- methods
Answer:
-Stare at the red square image below for 30 seconds. You may blink but should take care to keep your gaze
fixed.
-Shift your gaze to a piece of plain white paper and note the after-image. The image lasts for many
seconds. The image is inverted in contrast, hence the name 'negative afterimage'.
Question:
17. Negative Afterimages- results
Answer:
I saw a blue/yellow colored image
