The Eye and Retina

Question 1

Major anatomical structures in the eye

Answer 1

• Ciliary body
• Cornea
• Iris
• Retina
• Optic nerve
• Choroid
• Sclera

Question 2

Tunica of the eye

Answer 2

• Tunica fibrosa
• Tunica vasculosa
• Tunica interna

Question 3

Cell types in the retina

Answer 3

• Ganglion cells
• Amacrine cell
• Bipolar cell
• Horizontal cell
• Cone
• Rod
• Retinal pigment epithelium (RPE)

Question 4

Retinal pigment epithelium

Answer 4

Maintains photoreceptor health by transporting nutrients and recycling shed photoreceptor parts

Question 5

Bruch’s membrane

Answer 5

Extracellular matrix structure at the interface between the choroid and retina

Question 6

Rods and cones

Answer 6

Light-sensing photoreceptors

Question 7

Amacrine, bipolar and horizontal cells

Answer 7

Connecting neurons

Question 8

Ganglion cells

Answer 8

Transmit signals originating in the photoreceptor layer through the optic nerve and into the brain

Question 9

What type of stem cell have RPE, photoreceptors and ganglion cells been differentiated from?

Answer 9

Pluripotent stem cells

Question 10

What does the iris do?

Answer 10

Regulates light levels

Question 11

What is the pupillary constrictor?

Answer 11

Smooth circular muscle

Question 12

What is the pupillary dilator?

Answer 12

Smooth radial muscle

Question 13

Photopupillary reflex

Answer 13

Light reflex which changes pupil diameter

Occurs in both eyes even when only one is stimulated

Question 14

What is the pupil?

Answer 14

A hole in the retina

Question 15

What is a cataract?

Answer 15

A cloudy lens

Question 16

How do rods and cones differ?

Answer 16

Rods simply detect light whereas cones detect colour

Question 17

Where are cones concentrated?

Answer 17

Fovea

Question 18

How does the eye focus light?

Answer 18

• Light is partially focused when it passes through the cornea
• Then travels through the aqueous humour to the crystalline lens, which lets the eye focus on different depths
• The light converges in the lens and travels out the other side flipped, traveling through the vitreous humour to the retina on the inner back surface of the eye, where rods and cones detect light
• Then your brain presents a coherent, correctly-oriented image

Question 19

Resting potential of photoreceptors

Answer 19

• 40mV

Question 20

What type of polarisation occurs when light stimulates photoreceptors?

Answer 20

Hyperpolarisation

Question 21

Phototransduction steps

Answer 21

• Light entering the eye activates the opsin molecules in the photoreceptors
• Activated rhodopsin causes a reduction in the cGMP intracellular concentration
• The photoreceptor is hyperpolarized following exposure to light

Question 22

How is phototransduction terminated?

Answer 22

(1) Inactivation of rhodopsin occurs through phosphorylation by the opsin kinase, followed by the binding of arrestin to phosphorylated rhodopsin.
(2) Inactivation of transducin occurs through the hydrolysis of bound GTP to GDP (Tα-GTP to Tα-GDP) via an intrinsic GTPase activity that is accelerated by the GTPase activating protein RGS9 (regulator of G-protein signaling).
(3) Inactivation of phosphodiesterase (PDE) is coupled to the inactivation of transducin. Inactivated transducin (Tα-GDP) dissociates from PDE, resulting in a cessation of PDE-mediated cGMP hydrolysis.
(4) Activation of guanylate cyclase by guanylate cyclase activating protein (GCAP) restores cGMP levels and thus promotes the re-opening of cGMP-gated channels.

Question 23

A single photoactivated rhodopsin catalyses the activation of ____ transducin molecules

Answer 23

500

Question 24

a single activated rhodopsin can cause the hydrolysis of more than ____ molecules of cGMP per second.

Answer 24

10^5

Question 25

Duplicity theory

Answer 25

Can't have high sensitivity and high resolution in a single receptor, hence separate systems for colour and monochrome

Question 26

Types of bipolar cells

Answer 26

- ON | - OFF

Question 27

ON bipolar cells inhibition

Answer 27

Glutamate inhibits ON bipolar cells via metabotropic glutamate receptors

Question 28

OFF bipolar cells excitation

Answer 28

Glutamate excites OFF bipolar cells via inotropic glutamate receptors

Question 29

ON bipolar cell

Answer 29

- Hyperpolarised in the dark - Depolarised by central illumination - Metabotropic glutamate receptors - Conductance increases in light - Light response leads to loss of inhibition by glutamate

Question 30

OFF bipolar cells

Answer 30

- Depolarised in dark - Hyperpolarised by central illumination - Ionotropic glutamate receptors - Conductance decreases in light - Light response leads to loss of excitation by glutamate

Question 31

Retinal ganglion cell types

Answer 31

- W - X - Y - Melanopsin RGCs

Question 32

W cells

Answer 32

- Mainly from rods - Slow conducting - Broad fields, dendrites spread - Directional movement - Vision in low light

Question 33

X cells

Answer 33

- Medium conduction - Small fields, dendrites not spread - Image formation - Colour vision

Question 34

Y cells

Answer 34

- Fast conduction - Broad fields, dendrites spread - Rapid responses to changes in visual fields

Question 35

Melanopsin RGCs

Answer 35

- Large-slow-light responsive - Independent of rods and cones - Circadian rhythm

Question 36

Why is vitamin A important in our diet?

Answer 36

- It is the precursor for 11-cis-retinal which is important in light transduction - Vitamin A cannot be synthesised by humans

Question 37

Vitamin D on vision

Answer 37

- Preventing angiogenesis (new blood vessel formation) - Anti-inflammatory, inflammation plays a role in the development of age-related macular degeneration (AMD) - Vitamin D may help prevent dry eyes by inducing cathelicidin, an anti-microbial protein that can be produced by cells in the eyes and heal eye wounds