Strabismus

Question 1

Strabismus - background

Answer 1

1. Def = squint/misalignment of eyes, so that they appear to point in different directions
2. If strabismus develops in the first 7y, it can have a significant effect on visual development
3. Newborn babies usually have transient misalignments up to 3mo of age; any infant with squint should have red reflexes checked, and those persisting >3mo of age should be referred to an ophthalmologist

Question 2

Strabismus - causes

Answer 2

1. Idiopathic
2. Refractive error
3. Visual loss (e.g. cataracts, retinoblastoma - ?)
4. Ophthalmoplegia - central
5. Ophthalmoplegia - peripheral

Question 3

Strabismus - types (2, 3+2)

Answer 3

1. Concomitant (non-paralytic, common) - (3)
   a. Usually due to refractive error in one or both eyes (tx with correction with glasses but may require surgery
   b. Particularly common in children with neurodevelopmental delay
   c. Squinting eye most often turns inwards (convergent), but there can be outward (divergent) or rarely vertical deviation
2. Paralytic (rare) - (2)
   d. Varies with gaze direction due to paralysis of motor nerves
   e. Can be sinister bc of the possibility of underlying SOL such as a brain tumour

Question 4

Strabismus - description (3+1)

Answer 4

1. Convergent = bad eye turned inwards (cross-eyed appearance)
2. Divergent = bad eye turned outwards
3. Latent = squint that is controlled by subconscious effort; not always apparent. In certain situations, e.g. fatigue, the control is lost and the squint will ‘manifest’

+ pseudosquint = when wide epicanthic folds give the appearance of a squint; excluded on testing

Question 5

Strabismus - ex/ix

Answer 5

1. Corneal light reflex test (3)
   - Used to detect squints.
   - Use pen-torch held at a distance to produce reflections on both corneas simultaneously.
   - Light reflection should appear in the same appearance in the two pupils. If not, a squint is present
2. Cover test (3)
   - When squint is present and the fixing eye (good eye) is covered, the squinting eye moves to take up fixation
   - Child’s interest should be attracted with a toy or light. Occlude eye with card or plastic occluder
   - Test performed with object near (33cm) and distant (>6m), as certain squints are present only at one distance

Question 6

Strabismus - mx

Answer 6

1. Aim of tx = weaker squinting eye trained up in order to prevent amblyopia. Tx usually under supervision of orthoptists (allied health for eyes) in cooperation with ophthalmic surgeons
   ____
2. Correct refractive error - wear glasses
3. Eye patch wearing on the good eye to ‘train’ weaker eye
4. Eye muscle exercises
5. Eye (muscle) surgery if large squint and above measures failing

Question 7

Strabismus - referral to ophthalmologist (3)

Answer 7

Child must be seen by ophthalmologist if squint is:

1. Divergent
2. Paralytic
3. Persistent >2mo

Question 8

Amblyopia - overview + mx (2+3)

Answer 8

1. Def = permanent loss of visiual acuity in an eye that has not received clear images in the sensitive period of visual development (up to age 7y)
2. Most commonly due to squint, but may also develop with refractive errors and cataracts.
   - Refractive errors = cause a poorly focused image to be transmitted from the retina to the cortex. Such input does not stimulate normal cortical development and amblyopia results
   - Strabismic (misaligned) eyes each send a different view of the world to the cortex. If the brain paid attention to the image from each eye, diplopia would ensue. However, the immature visual cortex is capable of ignoring the image from one eye -> cortex may eventually suppress input from deviating eye -> amblyopia

Mx = regular orthoptic monitoring with ongoing correction of refractive error in ‘lazy’/weaker eye is required

3. Correct refractive error = with glasses
4. Eye patching = attempt to reverse amblyopia, by covering the better eye to force the ‘lazy eye’ to work
5. Eye (muscle) surgery)