In a case of orbital trauma where shining a light into the affected eye causes the contralateral pupil to constrict, what defect is indicated?

In this scenario, when shining a light into the affected eye leads to constriction of the contralateral pupil, it indicates an afferent pupillary defect, often referred to as a Marcus Gunn pupil. This occurs when there is a defect in the sensory pathways that detect light, typically due to damage in the retina or optic nerve of the affected eye.

In a healthy eye, shining light in one eye causes both pupils to constrict due to a direct and consensual response. However, if the affected eye has a compromised afferent pathway, there is reduced sensory input from that eye. As a result, the affected eye has a diminished pupillary reaction, while shining light in the unaffected eye still stimulates both pupils to constrict. This creates a paradoxical response where shining light into the affected eye results in less constriction or even a dilation of that pupil relative to the unaffected side, leading to the observation of increased constriction of the contralateral pupil when assessed.

The remaining options pertain to other types of pupillary responses. An efferent pupillary defect would indicate a problem with the muscles or pathways responsible for pupil constriction, which is not demonstrated by this case. The statement about both pupils remaining equal would suggest