Melanopsin Driven Pupillary Light Response in Leber’s Hereditary Optic Neuropathy (LHON)

Abstract

Purpose: : Though there may be massive loss of retinal ganglion cells (RGCs) in Leber’s Hereditary Optic Neuropathy, there is evidence of selective sparing of the 1% of RGCs that express melanopsin (mRGCs). (1,2) To evaluate the physiology of the mRGCs in this optic neuropathy, pupillary light responses (PLRs) were recorded.

Methods: : 12 patients (9 males) with LHON (47.8±14.1 yrs) and 12 healthy subjects (3 males) (38.7±15.9 yrs) were tested. Pupil light responses (PLR) were measured with an eye tracker (Arrington Research Inc.) and the stimuli were controlled with a Ganzfeld system (Roland Consult). Subjects were dark adapted for 10 minutes and pupil responses were measured monocularly, using 1s, 250 cd/m2 flashes. (3) Blue (470 nm) and red (640 nm) flashes were presented at 1 min intervals. The peak amplitude and latency of the transient PLR was measured. To assess the melanopsin-driven PLR (mR), the median amplitude between 4 and 6 s after the offset of the blue flash was measured. (3)

Results: : The mR was present in all controls (C) and in 9 of 12 patients, which were subdivided into mR and non-mR groups. No difference was found for transient PLR latencies among the three groups (mR, non-mR, C). Peak amplitudes did not differ between C and mR groups, but the non-mR group differed from both (p<0.05). The mR amplitude was larger for the blue than for the red stimuli, consistent with a sustained response driven by the mRGCs. This response differed among all groups (p< 0.05) for the blue stimulus, being greater in the control group.

Conclusions: : The melanopsin-driven PLR is present in LHON patients; although it is diminished in some, it is normal in others. Further tests are needed to investigate a possible relationship of these findings to the relative sparing of mRGCs reported in patients with LHON. (1,2)

Keywords: pupillary reflex • neuro-ophthalmology: optic nerve • ganglion cells