EVIDENCE FOR PRESERVED DIRECT PUPILLARY LIGHT RESPONSE IN LEBERS HEREDITARY OPTIC NEUROPATHY

Aims/Background-Pupillary light response is usually defective in all t ypes of optic neuropathy. However, the authors have observed in patien ts with Leber's hereditary optic neuropathy (LHON) relatively normal l ight response, with consequent misdiagnosis psychogenic visual loss in some cases. To confirm this clinical impression, afferent pupillary d efect was assessed by measurement of adjusted constriction amplitude ( CA) and escape rate (ER) by infrared videopupillography (Iriscorder-C 2515). Methods-Thirteen consecutive patients (26 eyes) with LHON (aver age age 27.2 years) were examined; 12 had the mitochondrial DNA 11778 mutation and one the 14484 mutation. Seven of these patients had a pos itive family history. For comparison, the above rates were determined in 19 patients (23 eyes) with idiopathic optic neuritis (ON; average a ge 35.1 years), 18 patients (19 eyes) with anterior ischaemic optic ne uropathy (AION; average age 58.1 years), and 25 volunteers (50 eyes) w ith healthy eyes (average age 39.6 years). Results-The distribution of visual acuity was essentially the same in all optic neuropathy groups . Reduction in CA and increase in ER were significant in patients with ON and AION, but not in those with LHON. Only slight afferent pupilla ry defect was evident even 2 years after the onset of LHON. CA in AION and ER in ON were correlated statistically with visual acuity and Hum phrey mean threshold deviation, while CA and ER in LHON were not. Conc lusion-Pupillary light response in patients with LHON obviously differ s from that in patients with other types of optic neuropathy. LHON app ears to be pathophysiologically characterised by well preserved affere nt fibres for pupillary light response (probably from W cells). Beside s being of pathogenetic interest, the detection of clinical features s hould facilitate the diagnosis of LHON particularly when family histor y provides no indication.