Clinical Optics

Question 1

what is eye refractive index?

Answer 1

manifestation of the refractory components of the eye (cornea, aqueous humour, lens and vitreous humour), their refractive indices and length of the eye

Question 2

what is a refractive error?

Answer 2

occur when eye is unable to focus light

Question 3

what are the clinical features of refractive errors?

Answer 3

Double vision, haziness, flare or halo around bright lights, squinting, headaches, eye strain

Question 4

what is myopia?

Answer 4

short sightedness

Question 5

what is hypermetropia?

Answer 5

long-sightedness

Question 6

what are the causes of myopia?

Answer 6

Unclear
Hereditary component
Link between myopia, academia and occupation
Environmental?

Question 7

what are the causes of hypermetropia?

Answer 7

Physiological – variation of normal, hereditary
Pathological – developmental abnormality, trauma
Functional – presbyopia, age

Question 8

what are the causes of astigmatism?

Answer 8

Hereditary
Trauma or surgery
Keratoconus

Question 9

what is the pathophysiology of myopia?

Answer 9

Parallel rays of light entering the cell focus at a point short of retina
Due to length – too long or
Refractive – too curved or lens too thick, corneal flattening

Question 10

what is the pathophysiology of hypermetropia?

Answer 10

Rays of light entering eye focus at a point beyond retina

Eyeball is too short, or the lens/cornea become thinner + flatter

Question 11

what is the pathophysiology of astigmatism?

Answer 11

Cornea has irregular curvature

Light enters at different points and are focused differently

Question 12

how is myopia denoted?

Answer 12

(-) meaning negative lens is required to correct?

Question 13

how is hypermetropia denoted?

Answer 13

(+) meaning positive lens are required to correct

Question 14

what are the clinical features of myopia?

Answer 14

Blurry vision when looking at things far away

Increased risk of retinal detachment (retinal stretching)

Question 15

what are the clinical features of hypermetropia?

Answer 15

Blurry vision when looking at shirt distances

Headaches, squinting

Question 16

what are the clinical features of astigmatism?

Answer 16

Blurred vision at all distances
Headaches
Difficulty driving at night

Question 17

how is myopia treated?

Answer 17

Glasses (divergent/negative lens/concave)

Not required if asymptomatic

Question 18

how is hypermetropia treated?

Answer 18

If asymptomatic no treatment

Positive dioptric powered lens (converging)

Question 19

how is astigmatism treated?

Answer 19

Cylindered lens

Question 20

what is presbyopia?

Answer 20

Reduction of accommodation

Question 21

what is the cause of presbyopia?

Answer 21

ageing

Question 22

what is the underlying mechanism of presbyopia?

Answer 22

Lens become less elastic, ciliary body loses ability to contract

Question 23

what are the clinical features of presbyopia?

Answer 23

Difficulty with near vision

Question 24

what is the management of presbyopia?

Answer 24

o	Convergent (+) lens
o	Simple reading glasses
o	Bifocal or varifocal lens

Question 25

what are the causes of squints?

Answer 25

refractive, non-refractive, mixed, nerve palsies, myogenic, cataract, paralytic, non-paralytic, retinoblastoma

Question 26

what is a exotropia squint?

Answer 26

Divergent squint (affected eye looks outwards) – divergent angle between eyes

Question 27

what is a esotropia squint?

Answer 27

Convergent squint (affected eye looks inwards) – convergent angle between eyes

Question 28

what is a hypertropia squint?

Answer 28

Upwards vertical squint (affected eye looks up) – one eye is lower to the other

Question 29

what is a hypotropia squint?

Answer 29

Downwards vertical squint (affected eye looks down) – one eye is superior

Question 30

what is a manifest squint?

Answer 30

Present all the time and is referred to as a “tropia”

Question 31

what is a latent squint?

Answer 31

On present on dissociation of the eyes and is referred to as a “phoria”

Question 32

what are the clinical features of squints?

Answer 32

* Misalignment of the eye * Double vision * Eye strain

Question 33

how are squints diagnosed?

Answer 33

* Visual Acuity * Alignment of the visual axes * Cover/Uncover test * Alternate Cover Test * Assess ocular movements * Fundoscopy

Question 34

what is the cover/uncover test?

Answer 34

o Cover the squinting eye. The unaffected eye will not deviate o Cover the unaffected eye. The squinting eye will move to take up fixation o Since eye movements are equal and opposite then as the squint moves to take up fixation, the unaffected eye also moves. o Remove the cover from the unaffected eye. The unaffected eye will resume fixation and the squint will return to it’s original position.

Question 35

what is the alternate cover test?

Answer 35

Move the cover rapidly between the two eyes. This dissociates the eyes and will show if there is a latent squint.

Question 36

what is the management of squints?

Answer 36

3Os o Optical – assess refractive state – spectacles for correction o Orthoptic – patching good eye encourages use of the one which squint o Operation - resection and recession of rectus muscles