Lecture 22 Secondary strabismus

Question 1

How can you predict the direction of deviation in someone with secondary strabismus?

Answer 1

impairment of vision occurs between 6 months to 7 years: esotropia

impairment of vision occurs at 8 or above: exotropia

Question 2

What is the aetiology of secondary strabismus?

Answer 2

*Anisometropia/aphakia
*Congenital or traumatic cataract
*Injury/trauma Corneal opacity
*Macular lesions
*Glaucoma
*Optic atrophy
*Retinoblastoma
*Secondary to sight-saving surgery

Question 3

What are the ways of measuring deviation angle?

Answer 3

prism reflection test: assess CR and then place prism in front of deviating eye until CR are central.

-krimsky test: prism is placed over fixing eye. Trying to get CR central in both eyes.

-Hirschberg’s test: no prism. Assess how much CR is deviated. For EVERY 1MM OF DISPLACEMENT IS EQUAL TO 7 DEGREES WHICH IS EQUAL TO 15 PRISM DIOPTRES.

Question 4

How do you decide if you should test BSV in someone with secondary strabismus?

Answer 4

*Only assess for this if onset was after aged 2 years as we know their BSV has developed so we want to see if we can get that back
*Only test if VA allows. If NPL in eye, won’t be able to restore BSV
*Important when planning for surgery

Question 5

What types of strabismic surgery can you do?

Answer 5

*Esotropia: aim to leave the eye slightly under corrected (leave them a bit eso). Overtime, eyes naturally diverge.

*Exotropia: aim to slightly overcorrect (make px slightly eso).

*Adjustable strabismus surgery allows for fine tuning alignment in cases of blind/severely sigh impaired. (We can fine tune alignment once px is awake and tie off suture after the surgery)

Question 6

What are the conservative treatment options for secondary strabismus?

Answer 6

occlusive contact lenses
-frosting of glasses lens
-optical adaptation-increases blur with glasses
-corneal tattoo
-intraocular occlusive lens

Question 7

1. When can BTXA be used?
2. How does it work?
3. How long does it last?

Answer 7

1. -Can use therapeutically for temporary realignment of the eye.
   -Can use it diagnostically: prepare for surgery to assess post-operative risk.
2. • Botulinum toxin paralyses the muscle.
     *There is no down time. It’s an outpatient procedure. Can return to work on the same day.
     *Local anaesthetic is used on muscle (proxy, oxy)

*Esotropia: inject medial rectus. Lateral rectus pulls eye outwards making it more central.
*Exotropia: inject lateral rectus. Medial rectus will pull eye inwards into central alignment.

3. • Effect is only temporary. Average time toxin works for is 3 months. Not the same for ever px.
     *There is no limit to the number of injections a px can have so they can come back .