Vision 1

Question 1

Define refraction accomadation and refractive errors?

Answer 1

Refraction - Bending of light rays as they move from one medium to another

Accomadation - Altering lens shape, pupil size, eye convergance to alter how much we refract the light

Refractive Errors - Mismatches in light ray refraction

Question 2

What kind of lens causes conversion and what kind causes divergence?

Answer 2

A biconvex lens converges light rays

A biconcave lens diverges light rays

Question 3

What refractive media are in the eye?

Answer 3

• Cornea
• Aqueous Humor
• Lens
• Vitreous Humor

The cornea is the biggest bender but the lens is capable of varying its refractive power (accomadation)

Question 4

At what distance will all light rays reaching the eyes be parallel?

Answer 4

6m and beyond

Question 5

How does lens thickness change as the object moves closer to the eye?

Answer 5

It gets thicker because:

• The close the object the more divergent the rays reaching the eyes
• So the greater the refractive power required

Question 6

How does the lens thicken?

Answer 6

• > Parasympathetic stimulus
• > Ciliary muscle contracts
• > Makes ciliary muscle bulge
• > Causes suspensory ligaments to go lax
• > Lens stretch decreases and lens gets thicker

Question 7

How does pupil constriction affect focus?

Answer 7

The closer the object the more the pupil constricts to minimize the rays getting through

Question 8

How does the pupil constrict?

Answer 8

Cranial Nerve III (Oculomotor)

• > Parasympathetic fibres
• > Sphincter Pupillae Muscle Contracts

Question 9

What causes our eyes to converge to focus on closer objects?

Answer 9

Cranial Nerve 3 (Oculomotor)
-> Stimulates Both Medial Recti

Because we do so much close work our medial recti have become thicker than our lateral recti

Question 10

What do we call the condition of having perfect eyesite?

Answer 10

Emmetropia i.e. you are an emmetrope

Question 11

List some common refractive errors?

Answer 11

Myopia - Short Sightedness
Hyperopia - Long Sightedness
Astygmatism - Non-spherical cornea/lens
Presbyopia - Age related long-sightedness

Question 12

What causes myopia?

Answer 12

The persons eyeball is slightly longer than normal

Causes the refractive power of the eye to be excessive and the rays converge before hitting the retina

Question 13

How does myopia affect close vision?

Answer 13

It doesn’t because close up the excess refractive power of the eye does the job without needing to use your lens

Question 14

How does myopia affect distance vision?

Answer 14

Further away objects are seen with less divergent rays so the over-refractive nature of the myopic eyeball means you cant focus the image on the retina even with the ciliary muscle fully relaxed

Question 15

How would you detect a myopia in kids?

Answer 15

• Infants may show a divergent squint
• Toddlers may lose interest in sports/people and instead focus on books/pictures
• Difficulty seeing or losing interest in class
• Headahces

Question 16

How do you treat myopia?

Answer 16

Need to reduce refractive power:

• Biconcave lenses or glasses
• Lasic

Question 17

What causes hyperopia?

Answer 17

Either the eyeball is too short or the cornea/lens is too flat
So the bending power of the eye is less than normal and the light rays converge behind the retina

Question 18

How does hyperopia affect closeup/distance sight?

Answer 18

The person has to use more accomadative power (a more convex lens) than usual to see distant objects.’

By the time an obect gets close the person doesnt have enough accomadative power to focus the rays so close up objects are blurry

Question 19

How would Hyperopia show up in a kid?

Answer 19

Convergent Squint

Symptoms of eyestrain after reading/working close up

Question 20

How would we treat hyperopia?

Answer 20

• Biconvex Lens/glasses

- Laser Eye Surgery

Question 21

Define an Astigmatism?

Answer 21

Non-spherical Curvature of the cornea or lens.

I.e. the eye is more like a rugby ball than a football

Question 22

How does astigmatism affect sight?

Answer 22

Because the cornea/lens is no longer spherical, the bending of light will never line up in one axis with another, therefore all objects will appear hazy

Question 23

How would we treat Astigmatism?

Answer 23

• Toric Lenses
• Laser Eye Surgery
• Cylindrical Glasses (curved in only 1 axis)

Question 24

Define Presbyopia?

Answer 24

Age related long-sightedness

With age the lens gets less elastic/mobile so the ciliary muscle isnt capable of thickening it as much as before.
Therefore you cant focus close up

Question 25

How do we treat presbyopia?

Answer 25

Biconvex “reading Glasses”

Most people in their 5th decade on have them.

Question 26

Define phototransduction?

Answer 26

The conversion of light energy to electrochemical signals

Question 27

Explain the process of phototransduction?

Answer 27

Opsins (in cones) and rhodopsin (in rods) contain chromophore 11-cis retinal.

When struck by a photon 11-cis retinal isomerizes to all-trans retinal.

All-trans retinal leaves the opsin triggering a signal transduction cascade that leads to closure of na/ca channels.

Leads to hyperpolarisation of the photoreceptor cell which triggers an action potential

Question 28

Explain the bleaching effect of phototransduction?

Answer 28

The visual pigment 11-cis retinal provides a purple colour to the retina.

When its all been struck by photons and converted/lost it leaves the retina temporarily bleached

Question 29

How is the visual pigment regenerated?

Answer 29

All-Trans Retinal is recycled into 11-cis retinal.

However some is lost and some forms retinyl esters, this is replaced using dietary vit A

Question 30

How would we detect vitamin A deficiency in the eye?

Answer 30

• Night Blindness
• Abnormal conjunctiva/corneal epithelium (Vit A important to epithelial health)
• Bitot’s spot (White/silvery) in conjunctiva
• Corneal Ulcer