CET feedback: Binocular Vision VRICS – 2 Ocular motility and strabismus

There were four cases to consider, each with three questions. The videos are still available online linked to this feature.

Patient MJ, an eight-year-old boy, had been advised to have an eye examination. His mother had long suspected that ‘his eyes sometimes look funny’. At a recent visit to the GP, she had been reassured that all was well, though she suspects this might have been due to MJ misbehaving at the visit.

Q1 What best describes his eye movements on laevoversion?

Q2 What best describes his eye movements on dextroversion?

Q3 What observation regarding the right palpebral aperture is correct?

This is a classic Duane retraction syndrome. It may be classified as a Type III as it shows limitation in both abduction and adduction in the right eye. On attempted adduction, there is a reduction in the palpebral aperture size due to the eye retracting, and therefore not keeping the lids pushed open. Once considered to be due to a fibrosed muscle (this case would most likely have been a fibrosed right lateral rectus), more recent evidence shows the underlying abnormality in many cases is a miswiring of the nerve supply to the lateral and/or medial recti. This is thought to be due to a minor brain stem developmental abnormality and results in co-contraction of these muscles. The innervation, rather than relaxation, of the antagonist muscles (the medial rectus is the antagonist to abduction, lateral rectus to adduction) restricts the action of the contracting muscle and therefore the lateral movement of the eye.