To the Editor.
—In their article Lhermitte et al1 failed to mention the possibility of the most likely cause of monocular failure of light perception with relatively intact pupillary reflexes, namely, a functional elaboration of what presumably was a partial visual loss due to an episode of opticneuritis in this patient. Before postulating a dissociation of light perception and pupillary reflex pathways, which is extremely rare if it occurs at all, it would seem appropriate to consider this possibility and to use some of the well-known examination techniques to try to establish or rule out a functional defect, such as stereopsis testing, the use of red-green glasses, and various methods of testing one eye while the patient believes that the other one is being tested.2 Visual evoked response testing might also be helpful.If such a dissociation does indeed exist, it suggests, as the authors postulate
Wertenbaker C, Kupersmith MJ, Behrens MM. Monocular Blindness With Preserved Pupillary Reflexes. Arch Neurol. 1985;42(6):515–516. doi:10.1001/archneur.1985.04060060013004
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