Relative afferent pupillary defect in a lesion of the pretectal afferent pupillary pathway

A 23-year-old man presented with Parinaud's syndrome due to a mixed germ cell tumour of the pineal gland. Following treatment the syndrome resolved, but the patient was noted to have a relative afferent pupillary defect (RAPD) without any detectable visual dysfunction. The authors localize the lesion to the pretectal afferent pupillary pathway and discuss the differential diagnosis of an RAPD in the presence of normal visual function.