Vision

Question 1

What is aqueous humour and what is its function in the eye?

Answer 1

It is transparent fluid that functions to provide nutrients and oxygen to the anterior chamber of the eye, and remove waste products.

Question 2

What structure in the eye secretes aqueous humour?

Answer 2

The ciliary body.

Question 3

What is Fuch’s Dystrophy?

Answer 3

It is a disease of the corneal endothelium, which results in central corneal clouding, loss of corneal sensation and the formation of epithelial bullae.

Question 4

What is Hypotony and why does it arise?

Answer 4

Hypotony is defined as an intraocular pressure of 5 mm Hg or less.

It is occurs when the rate of aqueous humour production is lower than the rate of aqueous humour outflow from the eye.

Question 5

What is Glaucoma and what is one of the main causes?

Answer 5

It is a group of eye diseases, which result in damage to the optic nerve and vision loss.

It is caused when the outflow of aqueous humour from the eye is blocked leading to an increase in pressure in the eye.

Question 6

What is a cataract?

Answer 6

A cataract is a clouding of the lens in the eye due to epithelial and fibre cell damage.

Question 7

What are Reactive Oxygen Species (ROS)?

Answer 7

ROSs are reactive chemical species that contain oxygen, formed as a natural byproduct during the metabolism of oxygen.

Question 8

How do Reactive Oxygen Species (ROS) cause the formation of cataracts?

Answer 8

An increase in ROS can cause oxidative stress in the eye. This oxidative stress can lead to epithelial and fibre cell damage and the progressive formation of a cataract.

Question 9

What causes oxidative stress to arise?

Answer 9

Oxidative stress is caused by the imbalance between the production of reactive oxygen species (ROS) and the body’s ability to detoxify the reactive intermediates or repair the resulting damage.

Question 10

Which two non-enzymatic antioxidants are able to detoxify the reactive intermediates that form Reactive Oxygen Species (ROS)?

Answer 10

Vitamin C and Glutathione.

Question 11

What enzymatic antioxidant is able to repair the epithelial damage caused by Reactive Oxygen Species (ROS)?

Answer 11

Catalase

Question 12

In which layer of the retina are the axons of ganglion cells located?

Answer 12

They are located in the nerve fibre layer.

Question 13

In which layer of the retina are the rods and cones (photoreceptor cells) located?

Answer 13

They are located in the outer nuclear layer.

Question 14

In which layer of the retina are Amacrine, Bipolar and Horizontal cells located?

Answer 14

They are located in the inner nuclear layer.

Question 15

What is the Fovea Centralis?

Answer 15

The Fovea is the centre of the visual field composed entirely of closely packed cones.

Question 16

Which photoreceptor is responsible for peripheral vision and vision in low light?

Answer 16

The Rods.

Question 17

What are the three types of cones and what differs between them?

Answer 17

L type (red), M type (green) and S (blue) type.

They are each sensitive to different colours of the visible light spectrum.

Question 18

Why do rods enable vision in low-light conditions?

Answer 18

They contain Rhodopsin, which is extremely sensitive to light.

Question 19

Which two colours are Rods sensitive to?

Answer 19

Blue and green.

Question 20

Primates, Birds, Reptiles and Fish have normal colour vision and they are sensitive to all three primary colours (red, gree and blue). What is this known as?

Answer 20

Being Trichromatic

Question 21

Which cells allows for the convergence of cone visual pathways in the retina?

Answer 21

Retina Bipolar Cells.

Question 22

What is Retinitis Pigmentosa and what is it caused by?

Answer 22

It is an inherited, degenerative eye disease that causes severe vision impairment. It arises due to the progressive degeneration of the rod photoreceptor cells in the retina.

Question 23

What is the mechanism of Phototransduction in the Rods and Cones?

Answer 23

1. The absorption of light inactivates a membrane current in the outer segment.
2. This results in the activation of the enzyme (PDE) that functions to convert cGMP to 5’ GMP.
3. The reduction in [cGMP] causes the Na+ channels to close.
4. [Na+] become low leading to the photoreceptor outer segment membrane becoming hyperpolarised.
5. This results in Ca2+ channels closing and thus a decrease in [Ca2+].
6. This decrease results in a decrease in [glutamate] release.

Question 24

What accounts for the differences in colour sensitivity between the different types of cones?

Answer 24

Differences in colour sensitivities is due to the different types of opsins in the cones.

Question 25

What is the main excitatory neurotransmitter, and inhibitory neurotransmitter in the retina?

Answer 25

Glutamate = excitatory

GABA = inhibitory.

Question 26

What are Ganglion cells and what are their function?

Answer 26

Ganglion cells are a type of neuron that functions to receive visual information from the photoreceptors via two intermediate neurons: bipolar cells and amacrine cells, and transmit the information in the form of action potentials to the brain.

Question 27

What are the two main types of Ganglion cells and what are the differences between them?

Answer 27

Midget GCs respond highly to luminance contrast and temporal frequency, but weakly to colour contrast and spatial frequency.

Parasol GCs respond highly to colour contrast and spatial frequency, but weakly to luminance contract and temporal frequency.