Melanopsin Retinal Ganglion Cells and Pupil: Clinical Implications for Neuro-Ophthalmology.

Chiara La Morgia,Valerio Carelli,Michele Carbonelli

doi:10.3389/fneur.2018.01047

Abstract

Melanopsin retinal ganglion cells (mRGCs) are intrinsically photosensitive RGCs that mediate many relevant non-image forming functions of the eye, including the pupillary light reflex, through the projections to the olivary pretectal nucleus. In particular, the post-illumination pupil response (PIPR), as evaluated by chromatic pupillometry, can be used as a reliable marker of mRGC function in vivo. In the last years, pupillometry has become a promising tool to assess mRGC dysfunction in various neurological and neuro-ophthalmological conditions. In this review we will present the most relevant findings of pupillometric studies in glaucoma, hereditary optic neuropathies, ischemic optic neuropathies, idiopathic intracranial hypertension, multiple sclerosis, Parkinson's disease, and mood disorders. The use of PIPR as a marker for mRGC function is also proposed for other neurodegenerative disorders in which circadian dysfunction is documented.

Highlights

Melanopsin retinal ganglion cells are intrinsically photosensitive RGCs expressing the photopigment melanopsin [1, 2]
post-illumination pupil response (PIPR) blue-red was reduced in glaucoma patients compared to normals (p < 0.001) and Ocular Hypertension (OH) (p < 0.01)
The use of pupil light reflex (PLR) mediated by Melanopsin retinal ganglion cells (mRGCs), as a measure of mRGC function, is of particular relevance for neurodegenerative disorders for which there is already evidence of circadian and sleep dysfunction, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Huntington’s disease (HD)

Summary

Introduction

Melanopsin retinal ganglion cells (mRGCs) are intrinsically photosensitive RGCs expressing the photopigment melanopsin [1, 2] They constitute about 0.2–1% of total RGCs and contribute to the photoentrainment of circadian rhythms, through their projections to the suprachiasmatic nucleus (SCN), and to other anatomical structures devoted to non-image forming functions of the eye. These include pupil regulation through their projections to the olivary pretectal nucleus (OPN) in the midbrain [3,4,5] and brain structures relevant for emotional processing [6]. The contribution of mRGCs to pupil response has been evaluated using blue (470 nm) and red (640 nm) light, being the blue light able to maximally stimulating mRGCs [13,14,15]

Methods

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Discussion

Conclusion