Visual disturbances and weight gain

Abstract Figure 4 (see p 732) shows decreased abduction of the left eye consistent with a left abducens nerve lesion. The clinical finding of a left relative afferent pupillary defect denotes a deficit of the afferent visual pathway, anywhere from the retina to the optic tract. However a lesion causing optic nerve atrophy can be due to a primary retinal problem, optic nerve tumour, or asymmetric lesion of the optic chiasm. Usually a lesion of the chiasm or posterior to it (tracts to the lateral geniculate nucleus) will affect the optic discs bilaterally. Here the retina appeared normal on fundoscopic examination, hence the lesion must be of the optic nerve, or an asymmetric lesion of the chiasm. This is confirmed as the Humphrey's field analysis deficit affects only the left eye.