Vision

Question 1

Non-stretchy sclera plus intra-ocular pressure

Answer 1

Keep eye rigid, back surface smooth and stable, and distances between optics and retina correct

Question 2

Iris

Answer 2

Controls how much light enters the eye via the pupil.

Question 3

Cornea

Answer 3

Primarily responsible for focusing light rays

Question 4

Lens

Answer 4

Provides additional, variable “fine” focus

Question 5

Rod photoreceptors

Answer 5

Night vision

Question 6

Cone photoreceptors

Answer 6

Day vision

Question 7

Cone photoreceptors

Answer 7

Membrane - Outer segment
Nucleus and Axon - inner segment
Synaptic terminal (the end)

Question 8

Retinal processing

Answer 8

You can only see in detail with the very centre of your visual field

Question 9

Loss of peripheral vision

Answer 9

• Glaucoma

* Retinitis Pigmentosa

Question 10

Loss of central vision

Answer 10

Age-related macular degeneration

Question 11

Peripheral vision

Answer 11

Majority of the retina serves only coarse vision:-
• the visual image is optically blurred.
• the cone photoreceptors are large and widely spaced (separated by larger number of rods).
• the signals from many cones converge onto single ganglion cells.

Question 12

Central vision is very special

Answer 12

The fovea is specialised for high resolution:-
• good focus – overlying layers are absent
• only cone photoreceptors, primarily red and green
• which are narrow and closely packed
• the signals from the photoreceptors are kept separate throughout the primary visual pathway

Question 13

Off centre retinal ganglion cells

Answer 13

• central photoreceptor depolarised (red) by decreased illumination
• bipolar and ganglion cells depolarised by excitatory synapses

Question 14

On centre retinal ganglion cells

Answer 14

• central photoreceptor hyperpolarised (blue) by increased illumination
• bipolar cell depolarised by inverting synapse excites ganglion cell

Question 15

Parvocellular

Answer 15

• small field with strong surround
• fine resolution
• accurately follows changes in light
• needs stable image

Question 16

Magnocellular

Answer 16

• large field with weak surround
• coarse resolution
• transient responses to change
• responds well to fast movement

Question 17

Parvocellular

Answer 17

• selective inputs from “red” or “green” photoreceptors
• by comparing these responses they can encode wavelength
• RED vs GREEN

Question 18

Bistratified

Answer 18

• elective inputs from “blue” or “red+green” photoreceptors
• by comparing these responses they can encode wavelength
• BLUE vs YELLOW