Incomitant Strabismus/Module 5: Third (IIIrd) Cranial Nerve Palsy

Characteristics of IIIrd CN Palsy

With the exception of the LR and SO, the entire musculature of the eye, internal and external, is controlled by the oculomotor cranial nerve. Thus the clinical findings may vary greatly in III N palsy, depending on whether it is complete or incomplete/partial, the latter occurring in various forms. It is important to recognise the extent of the muscles that are affected as this could aid in determining the aetiology, and will have important treatment implications.

Sometimes after III N palsy, there is a characteristic pattern of recovery known as aberrant regeneration. This tends towards certain typical signs, which can involve the extraocular muscles, lid and pupil.

Non-Surgical & Surgical Management

The immediate, non-surgical treatment options include prisms, occlusion and the use of a CHP if the ptosis does not cover the pupil and diplopia is a problem.

The choice of surgery is often complicated when treating III N palsy because of the widespread loss of muscle function. Aberrant regeneration can further complicate the situation.