Professional and Linguistic Assessments Board (PLAB) Practice Exam

What condition is characterized by impaired adduction of the eye on the same side as the lesion and horizontal nystagmus of the abducting eye on the contralateral side?

1. Internuclear ophthalmoplegia

2. Pseudoseizure

3. Multi-system atrophy

4. Parkinson's disease

The correct answer is: Internuclear ophthalmoplegia

Internuclear ophthalmoplegia is a condition that arises from a lesion in the medial longitudinal fasciculus (MLF), which is a bundle of nerve fibers essential for coordinating eye movements, particularly those involving adduction of the eye. In this condition, when an individual attempts to look to one side, the eye on the side of the lesion fails to adduct properly, resulting in impaired adduction. In contrast, the eye on the opposite side will exhibit horizontal nystagmus, a rapid involuntary movement, as it is forced to move unopposed to the side of the lesion. This characteristic presentation is crucial for differentiating internuclear ophthalmoplegia from other conditions that may affect eye movement but do not produce the specific pattern of deficits described. For instance, pseudoseizures are not related to eye movement coordination, while multi-system atrophy and Parkinson's disease involve broader motor control issues but do not specifically cause the classic eye movement abnormalities seen in internuclear ophthalmoplegia.