Eye Movements And Squint

Question 1

To maintain single vision what is required?

Answer 1

Fine coordination of eye movement of both eyes

Question 2

What is it called when the coordination of both eye movements is abnormal?

Answer 2

Squint

Question 3

What are other names for squint?

Answer 3

Strabismus

Tropia

Question 4

What is exotropia?

Answer 4

Divergent, one eye turned out squint

Question 5

What is esotropia?

Answer 5

One eye turned in, convergent squint

Question 6

What can produce a pseudo squint?

Answer 6

Prominent epicanthic folds

Question 7

What is the most common type of squint in children?

Answer 7

Esotropia (convergent)

Question 8

What can cause esotropia?

Answer 8

No cause

Hypermetropia (long sightedness)

Question 9

What is amblyopia?

Answer 9

A vision development disorder in which the eye fails to achieve normal visual acuity even with prescription eyeglasses or lenses.
Imbalance in the muscles that position the eye
Also called lazy eye
Begins during infancy
In most cases one eye affected
Breakdown in how brain and eye work together and brain can’t recognise sight from one eye (relies on other eye, so vision in weaker eye gets worse)
Early treatment works well

Question 10

What happens in strabismic amblyopia?

Answer 10

The brain suppresses the deviant image and the visual pathway does not develop normally

Question 11

What are the 2 broad categories of squint?

Answer 11

Non paralytic and paralytic - either can be convergent or divergent

Question 12

Describe non paralytic squints (concomitant)

Answer 12

Due to imbalance in extraocular muscles
The size of the deviation does not vary with direction of gaze
Most esotropias are non paralytic
Usually start in childhood

Question 13

Describe paralytic squint

Answer 13

Diplopia is most on looking in the direction of pull of the paralysed muscle

Question 14

How is a squint diagnosed?

Answer 14

Corneal light reflection test - hold a light source 30 cm from child’s face to see if light falls centrally (slightly nasal) and symmetrical on each cornea = normal. Asymmetrical if squint present, the reflection decentred in opposite direction to deviation

Cover test - identify nature of squint
As child to focus on object and cover one eye. Observe movement of uncovered eye. Cover other eye and repeat test

Movement of the uncovered eye to take up fixation as the other eye is covered demonstrates manifest squint. Latent squint is revealed by movement of the covered eye as the cover is removed

Question 15

What is cycloplegia?

Answer 15

Paralysis of the ciliary muscle by antimuscarinics- inhibiting accommodation

Question 16

What are the principles of squint management?

Answer 16

Optical - assess refractive state after cyclopentolate 1% drops - the cycloplegia allows objective determination of the refractive state, the mydriasis allows a good view of the eye to exclude abnormality e.g cataract, macular scarring, retinoblastoma, optic atrophy

Orthoptic - patching the good eye encourages use of the one which squints

Operation - resection and recession of rectus muscles - help alignment and give good cosmetic results. May use botulinum toxin instead of surgery

Question 17

Describe third nerve palsy

Answer 17

Ptosis
Fixed dilated pupil
Down and out
Proptosis - due to reduced recti tone

Question 18

What can cause third nerve palsy?

Answer 18

Raised ICP - tumour, haemorrhage
Aneurysm- posterior communicating artery
Vascular - secondary to diabetes, HTN (typically pupil sparing)
Cavernous sinus thrombosis

Question 19

Describe fourth nerve palsy (trochlear)

Superior oblique paralysed

Answer 19

Diplopia (worse on downward gaze)
Holding head in tilted position - ocular torticollis
The eye is looking up and in adduction, cannot look down

Question 20

What are some causes of cranial nerve 4 palsy?

Answer 20

Head injury
Any cause of raised ICP
Diabetes

• this nerve has the longest intracranial route, emerges from the dorsal aspect of brainstem (only nerve to do so)

Question 21

Describe sixth nerve palsy (abducens)

Innervates lateral rectus

Answer 21

Diplopia in horizontal plane

Eye is medically deviated and cannot move laterally from midline

Question 22

What can cause CN VI palsy?

Answer 22

Tumour causing raised ICP 
Trauma to base of skull
Vascular 
MS 
DM 

The nerve can be easily stretched due to it emerging anteriorly at the pontomedullary junction before running under surface of pons towards cavernous sinus