Relative afferent pupillary defect with normal vision and vertical strabismus—implications for pupillary pathway anatomy

Abstract

A relative afferent pupillary defect (RAPD) is usually a sign of visual dysfunction. Here, an unusual case of an RAPD combined with vertical strabismus but normal vision is described. Implications for pupillary pathway anatomy are discussed. A 12-year-old girl with chronic headache was shown to have a midbrain tumour. She presented to us with intermittent diplopia. Examination included visual acuity, visual fields, pupillary function, anterior and posterior segments, and strabismus evaluation with the tangent screen. There was a right-sided pathologic RAPD but no afferent visual impairment. Isocoria was present in light and darkness. There was a right-sided strabismus sursoadductorius. A pathologic RAPD with normal vision can be caused by tumour compression of the contralateral pretectal nucleus or its afferent or efferent fibres. As an implication for pupillary pathway anatomy, our case suggests that there is equal distribution between crossing and non-crossing intercalated neurons. An associated strabismus can show a non-paralytic pattern.