Exam #6: Vision

Question 1

What is accommodation? What are the physiologic events that give rise to accommodation?

Answer 1

1) Contraction of ciliary muscle
2) DECREASE in tension on suspensory ligaments
3) Lens RELAXES and become more spherical

*****This is used for NEAR vision

Question 2

What is presbyopia?

Answer 2

Age related decline in near-vision due to an inability to accommodate

Question 3

What is the blind spot?

Answer 3

Region of the optic disc WITHOUT photoreceptors

**Note that the optic disc is the head of the optic nerve in the retina

Question 4

What is the fovea?

Answer 4

• Depression in the macula, which is the area of maximal focus of the light i.e. best vision
• Avascular zone

Question 5

What is binocular disparity?

Answer 5

Difference in image location of an object seen by the left and right eyes, resulting from the eyes’ horizontal separation (parallax). The brain uses binocular disparity to extract depth information from the two-dimensional retinal images in stereopsis.

Question 6

What is prosopagnosia?

Answer 6

Patients with problems visually identifying faces

Question 7

What is object agnosia?

Answer 7

Patients with problems visually identifying objects

Question 8

What is scotoma?

Answer 8

Visual field defect

Question 9

Outline the position of the visual fields to the retina.

Answer 9

• Temporal visual field (monocular segment) projects nasally
• Nasal/ binocular segment projects to the temporal retina

Question 10

Where does the retina project?

Answer 10

• Optic chiasm
• Right ends up in left hemisphere
• Left ends up in the right hemisphere

**Only the nasal crosses

Question 11

What is the difference between the locations of rods and cones?

Answer 11

• Center of the fovea contains only cones that decrease laterally
• Lateral to the fovea, rods appear & increase in number

Question 12

What are the functional differences between rod and cone vision?

Answer 12

Rods= black & white

• Peripheral vision
• Nighttime vision

Cones= color

Question 13

Which receptor mediates scotopic vision? Photopic vision?

Answer 13

Scotopic= rods

• No color
• Poor acuity

Phototopic= cones

• High color
• High acuity

Question 14

What are the electrophysiological changes that occur when a photoreceptor is stimulated by light?

Answer 14

Dark= entry of Na+ & Ca++ via channels held open by cGMP
- DEPOLARIZED in DARK

Light=

• Decrease cGMP & Na+ & Ca++ DECREASE
• K+ leaves
• Cell hyperpolarized

**Dependent on glutamate release

Question 15

Define the term receptive field for visual neurons.

Answer 15

Area of the retina from which the neuron can be influenced

Question 16

Which retinal cell type can produce action potential?

Answer 16

Ganglion cells

Question 17

Which retinal cells are output cells?

Answer 17

Ganglion cells

Question 18

Which retinal cells capture photons?

Answer 18

Photoreceptors–rods & cones

Question 19

What is the function of retinal projections to the suprachiasmatic nuclei?

Answer 19

Hypothalamus: regulation of the circadian rhythms

Question 20

What is the function of retinal projections to the pretectal nuclei?

Answer 20

Reflex control of pupil and lens

Question 21

What is the function of retinal projections to the LGN?

Answer 21

This how we “actually see things”

Question 22

What is the function of retinal projections to the superior colliculi?

Answer 22

Orienting movements of the head & eyes toward visual stimuli

Question 23

What is the function of the dorsal visual stream to higher visual areas?

Answer 23

Motion and relative position of objects

Question 24

What is the function of the ventral visual stream to higher visual areas?

Answer 24

High level form vision & object recognition

Question 25

What is the clinical significance of having different pathways for different aspects of vision?

Answer 25

When the system breaks down, patients will have complex visual defects

Question 26

What are the pigments associated with rods, cones, and ganglion cells?
Where are the genes located that code for cone pigments related to color blindness?

Answer 26

• Three cone pigments:
  Red= x-chromosome
  Green= x-chromosome
  Blue= #7
• Rods= rhadopsin= #3
• Ganglion cells= melanopsin

Question 27

Outline the mechanisms for depth perception. Which are monocular and which require vision in both eyes?

Answer 27

Depth perception requires only MONOCULAR ques

• Size of the object
• Motion parallax

For really good depth perception, need binocular vision for stereopsis

Question 28

What is strabismus? Describe how strabismus can result in suppression of the visual image from one eye.

Answer 28

Strabismus refers to “squint” or cross-eyedness

• Causes one-eyed fixation
• Brain suppresses input from the other eye

Question 29

Which type of vitamin deficiency can cause night blindness?

Answer 29

Vitamin A

Question 30

Outline the pupillary light reflex. What is the different in function between the SNS & PNS?

Answer 30

PNS= contriction 
SNS= dilation

Question 31

What is the result of a lesion to the optic nerve?

Answer 31

Ipsilateral monocular blindness

Question 32

What is the result of a lesion to the optic chiasm?

Answer 32

Bitemporal hemianopsia

Question 33

What is the result of a lesion to the optic tract?

Answer 33

Homonymous hemianopsia

Question 34

What is the result of a lesion to Meyer’s Loop?

Answer 34

Superior quadrant anopsia