Vision 1

Question 1

What is refraction?

Answer 1

Light rays bending to form a sharp image on the retina

Question 2

What is accommodation?

Answer 2

Adapting focus between near and far away objects by changing how much we bend the light rays

Question 3

What are refractive errors?

Answer 3

A mismatch between how much we bend light rays

Question 4

What are the refractive media of the eyeball?

Answer 4

Cornea, lens, aqueous humour, vitreous humour

Question 5

What media has the most powerful refractive properties?

Answer 5

The cornea - 45D

Question 6

What media has the ability to alter its degree of refraction?

Answer 6

The lens

Question 7

What is the shortest range at which human eye can focus?

Answer 7

20cm

Question 8

What three actions take place to allow accommodation?

Answer 8

lens changes shape
pupil constricts
eyes converge

Question 9

Describe the process of the lens thickening

Answer 9

Ciliary muscle contracts making ciliary body bulge
Space in the middle decreases
Suspensory ligaments become lax
Lens is no longer under strain
Lens becomes thicker

Question 10

Describe the process of the pupil constricting

Answer 10

The pupillary constrictor is a concentric muscle around the border of the pupil which gets parasympathetic innervation. The parasympathetic innervation causes the muscle to contract and constrict the pupil

Question 11

Describe the process of the eyes converging

Answer 11

When looking at a close up object we use medical recited muscles of both eyes to converge. Converging is done more often than distance so the medial rectus muscles are much thicker then the laterals

Question 12

What is myopia?

Answer 12

Short-sightedness. Bending power of the eye is overused causing close objects to be seen clearly but far away objects to be out of focus

Question 13

What is hyperopia?

Answer 13

Long-sightedness

Question 14

What is astigmatism?

Answer 14

Non-Spherical curvature of the cornea or lens

Question 15

What is presbyopia?

Answer 15

Long-sightedness of old age

Question 16

What is emmetropia?

Answer 16

Perfect vision

Question 17

What is the most common cause of myopia?

Answer 17

Eyeball being too long

Question 18

Where do images form in relation to the retina in myopia?

Answer 18

In front of the retina

Question 19

Symptoms for myopia?

Answer 19

Headaches, inability to focus at distance, divergent squint in infants and preverbal children

Question 20

Correctional action for myopia?

Answer 20

Biconcave lenses - spectacles, contact lenses, laser eye surgery

Question 21

Causes of hyperopia?

Answer 21

Eyeball too short or cornea and lens too flat

Question 22

Where does an image form in relation to the retina in hyperopia?

Answer 22

Behind the retina therefore accommodation has to be used to see distant objects which should not need any increased bending power

Question 23

Hyperopia symptoms?

Answer 23

Eyestrain after working on computer, convergent squint in infants/children

Question 24

What can happen in children if hyperopia is not corrected?

Answer 24

Some vision in one or both eyes may be lost and the child may develop ‘lazy eye’

Question 25

Correctional action for hyperopia?

Answer 25

Biconvex glasses, contact lenses, laser eye surgery

Question 26

Correctional action for astigmatism?

Answer 26

Cylindrical glasses, toric contact lenses, laser eye surgery

Question 27

Aetiology of presbyopia?

Answer 27

Loss of mobility and elasticity in the lens with age, less malleability in the lens when the ciliary body contracts, seeing near objects becomes difficult

Question 28

Correctional action for presbyopia?

Answer 28

Biconvex reading glasses

Question 29

What is phototransduction?

Answer 29

The stimulation of photoreceptor cells on the retina by the energy in light waves - the conversion of light energy to an electrochemical response by the photoreceptors (rods and cones)

Question 30

Describe rods and cones

Answer 30

Rods and cones (the names reflect their respective shapes) contain light sensitive pigments. Each photoreceptor consists of an outer segment which contains hundreds of thin plates of membrane (lamellae). The outer segment is connected by a cilium to an inner segment which contains a nucleus. Rods are about 500 times more sensitive to light than cones, but cones give us colour vision.

Question 31

Which photoreceptors give us colour vision?

Answer 31

Cones

Question 32

Which photoreceptors are more sensitive to light?

Answer 32

Rods (~500times)

Question 33

Where in photoreceptors does pigment reside?

Answer 33

Within the cell membrane of the lamellae of the photoreceptor

Question 34

What pigment is found in rods?

Answer 34

Rhodopsin

Question 35

What pigments are found in cones?

Answer 35

Cone opsins S, M and L

Question 36

What makes up the pigment rhodopsin?

Answer 36

Opsin + 11-cis Retinal

Question 37

How does bleaching occur?

Answer 37

When light falls on rhodopsin, the 11-cis retinal isomerises to all-trans retinal. All-trans retinal cannot fit into the opsin and so rhodopsin splits. This results in the bleaching of the colour purple.

Question 38

How does bleaching of the visual pigment result in phototransduction?

Answer 38

The phototransduction cascade

Question 39

What role does vitamin A play in the visual pigment?

Answer 39

Key for visual pigment regeneration

Question 40

Give some conditions as a result of which Vitamin A deficiency is common

Answer 40

Malnutrition, malabsorption - coeliac disease, sprue

Question 41

What is the effect on the eyes of Vitamin A deficiency?

Answer 41

Any condition that affects Vit A absorption will affect vision and cause night blindness. Vit A is also essential for a healthy epithelium so the conjunctiva and corneal epithelium will also become abnormal

Question 42

What are some signs of Vitamin A deficiency seen in the eye?

Answer 42

Bitot’s spots in the conjunctiva, corneal ulceration, corneal melting which leads to further opacification of the cornea