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Editor,—Relative afferent pupillary defect (RAPD) is important in diagnosing lesions of the anterior visual pathways. RAPD is almost always present in unilateral optic nerve disease. Optic tract lesions are characterised by a combination of homonymous hemianopia and RAPD contralateral to the side of the lesion1 with subsequent, specific, asymmetric optic atrophy.2 In acute homonymous hemianopias RAPD has been used to differentiate between infrageniculate and suprageniculate lesions, since neither optic atrophy nor RAPD should occur in the presence of acquired affections of optic radiation or visual cortex.
Pupillary hemiakinesia—that is, reduced or absent pupillary light reaction after stimulus presentation in the blind field, is typical of optic tract lesions. However, we examined a young boy with unilateral involvement of postchiasmal visual pathways, homonymous hemianopia, and asymmetric optic atrophy due to a porencephalic substance defect, but without RAPD or pupillary hemiakinesia.
CASE REPORT
The 7 year old boy has been in ophthalmological care since shortly after birth because of horizontal nystagmus, strabismus, head posture (left head rotation), bilateral optic atrophy, and defective exploration of his right hemifield. Paediatric examination revealed a pathological left sided Babinski …