Sustained pupil constriction following brief light exposure: Relation to retinal health

The pupillary light reflex (PLR) is an indispensable clinical measure of visual, neurological and autonomic function which, until recently, was thought to be driven by only rods and cones. In 2000, a novel subset of retinal ganglion cells (RGCs) was discovered that express melanopsin and are intrinsically photosensitive (ipRGC). These ipRGCs contribute to the PLR and are responsible for the sustained pupilloconstriction observed following light offset (the post-illumination pupil response (PIPR)). The primary goal of this project was to examine the PIPR in a broad sample of the general human population. Using a newly-developed, wide-field optical system, we demonstrate that all normal subjects display a post-illumination pupil response in response to a 10-second, 470nm light stimulus. We demonstrated that this PIPR was not correlated with subject characteristics such as age, race and gender, and that the only factor affecting the magnitude of the PIPR was the baseline pupil diameter. In most normal individuals, the PIPR was substantial (mean = 1.4 mm), and this test therefore has the potential to be utilized as a tool in evaluating subjects with either retinal or melanopsin-related disorders.

Glaucoma is a group of diseases of the optic nerve that causes optic neuropathy (GON) associated with visual field loss. The second goal of the project was to test the PIPR in a group of patients with GON and compare the results with normal subjects and visual fields. Our results indicate that there was a significant difference between the GON patients and age-matched controls (p<0.05). We also demonstrated that the loss of PIPR correlated with the severity of visual field loss (as evidenced by the mean deviation (MD) loss).

In conclusion, using a newly-developed, wide-field optical system, we have demonstrated that all normal subjects display a post-illumination pupil response which is reduced in patients with GON. Thus, testing for PIPR has the potential to be utilized as a clinical tool in evaluating and following patients with GON or melanopsin-related disorders.

Keywords: ipRGC, glaucoma, optic neuropathy, pupillary light reflex.