Strabismus

Question 1

What is strabismus?

Answer 1

aka squint

is a misalignment of the two eyes

Question 2

How does amblyopia develop?

Answer 2

Amblyopia is when someone has a ‘lazy eye’.
If strabismus develops during the ‘sensitive period’ (up to 7-8 years of age) then the brain responds by refusing to see through that eye and so double vision is not seen. However, if the strabismus develops after the sensitive period at a later age, then there will usually be double vision.

Question 3

What is alternating strabismus?

Answer 3

This is when the eye that deviates alternates. This can be tested using the cover test. If the same eye returns to its strabismus position (not in alignment) then this is not alternating strabismus, but if the other eye moves into a strabismus position then it is called alternating strabismus.

Question 4

What are latent and manifest deviations? and the difference between phoria and tropia?

Answer 4

A ‘latent’ deviation or phoria is one that is contorlled by subconcious effort. in certain situations such as fatigue, control is lost and deviation becomes ‘manifest’.
A latent squint is a ‘phoria’ and a manifest deviation is a ‘tropia’

Question 5

What are the various terms for the position of the strabismus eye?

Answer 5

eso (converge)
exo (diverge)
hypo (down)
hyper (up)

Question 6

What is ambylopia?

Answer 6

Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to process inputs from one eye and over time favors the other eye. It results in decreased vision in an eye that otherwise typically appears normal.

Question 7

What questions should you ask for strabismus hx?

Answer 7

age of onset of strabismus
maternal infection
birth trauma
illness
family hx
raised intracranial pressure and other neurological diseases.

Question 8

What is the treatment for strabismus?

Answer 8

1) correct any refractive error (glasses)
2) reverse the amblyopia - occlude the better-seeing eye, this forces the amblyopic eye to force fixation. However non-compliance is a significant problem.
3) orthoptic management
4) surgery - for cosmesis only

Question 9

What is apparent pseudo convergence?

Answer 9

is common and seen in very young eyes that usually have a wide nasal bridge and vertical folds of the skin at the epicanthal folds.

Question 10

What are the main causes of strabismus in childhood?

Answer 10

idiopathic
refractive error
visual loss
central or peripheral neuro deficit

Question 11

What are the key features of a convergent squint?

Answer 11

early onset and non-refractive OR
later onset and hypermetropic usually OR
Duane’s syndrome/6th nerve palsy

Question 12

What are the key features of a divergent squint?

Answer 12

idiopathic
myopia
secondary to visual loss

Question 13

What different types of refractive error are there and how are they corrected?

Answer 13

myopia: short sighted - fix using a concave lens
hypermetropia - longsighted - fix using convex lens
astigmatism - requires a rugby shaped lens rotated 90 degrees
anisometropia - the refractive error differs significantly between the two eyes

Question 14

What are the possible causes of a whitish lesion obstructing the red reflex in one eye in a 4 year old?

Answer 14

retinoblastoma - a malignant tumour of the retina which is often inherited and could be bilateral.
cataract- opacity of lens, may be unilateral or bilateral
toxocara and toxoplasma - an infection which is usually acquired in infancy.

Question 15

Explain the etiology of adult squint; afferent, central and efferent.

Answer 15

afferent - visual loss
central - decompensation of a childhood squint, or disturbance of control centres
efferent - cranial nerves 3, 4 and 6, neuromuscular function or extraocular muscles

Question 16

What is comitant vs incomitant strabismus?

Answer 16

comitant is when the angle of deviation remains constant throughout all eye movements while in incomitant strabismus, there is restricted eye movement and the angle of deviation varies with gaze. in incomitant one eye is usually fixed in one place.

Question 17

What does the cover uncover test reveal vs the alternate cover test?

Answer 17

The first cover uncover test will identify any gross manifest tropias. The cover alternate test will identify and reveal any latent phorias.

Question 18

is ambylopia likely to occur in those with alternating contaminant esotropia?

Answer 18

no as not one eye’s neural pathways are likely to become less developed. Ambylopia mostly occurs when one eye is affected and has a tropia.

Question 19

What is the treatment or management plan for a child with alternating contaminant esotropia?

Answer 19

Full history and examination to rule out other eye pathology. Refraction to address any hypermetropia (which can cause an esoptropia), glasses if required, and finally surgery to address any residual esotropia.

Question 20

WHat is dacryocystitis?

Answer 20

Dacryocystitis, inflammation of the lacrimal sac secondary to obstruction at the nasolacrimal duct at the junction of the lacrimal sac. Management - observation, massage and probing if older than 12 months. Usually resolves at age 1.

Question 21

What is the correct medical term for the appearance of a white red reflex of the pupil?

Answer 21

leukocoria

Question 22

how do you undertake the red reflex test?

Answer 22

Use an ophthalmoscope to assess the eye from approximately a 1/3rd of a metre away so that the light is falling on both eyes at the same time. Viewing through the ophthalmoscope, dial in ‘plus’ lenses until the iris and then the red reflex is seen clearly (about +3). As some of the light entering the eye is reflected back by the retina, an even red glow is usually obtained. Any opacities within the normally transparent structures of the eye will cause dark obscuration of the red reflex. Cataract is the most common cause of obscuration of part or all of the red reflex.