Abstract
Purpose :
To evaluate rod-, cone-, and melanopsin-mediated pupillary light reflexes (PLRs) as indices of neural dysfunction in diabetic patients who have different stages of non-proliferative diabetic retinopathy (NPDR).
Methods :
PLRs elicited by full-field, brief-flash stimuli were recorded from 50 diabetic patients (no NPDR [N = 17], mild NPDR [N = 16], moderate-severe NPDR [N = 17]) and in 25 age-equivalent, visually-normal controls. Subjects were dark-adapted for 10 minutes and the PLR was recorded in response to short-wavelength flashes (0.001 cd/m2: rod condition; 450 cd/m2: melanopsin condition). Subjects were then exposed to a short-wavelength, rod-suppressing luminance field and 10 cd/m2 long-wavelength flashes were presented (cone condition). PLRs were quantified as the maximum transient constriction (rod and cone conditions) and the post-illumination pupil constriction (melanopsin condition), relative to the baseline pupil size.
Results :
The mean baseline (pre-stimulus) pupil diameter was significantly smaller for the NPDR patients, both in the dark (p < 0.001) and in the light (p = 0.002), consistent with previous literature. A two-way ANOVA indicated significant effects of subject group (control, no NPDR, mild NPDR, moderate-severe NPDR; p < 0.001) and condition (rod, melanopsin, cone; p < 0.001) on the PLR. There was also a significant group by condition interaction (p < 0.001). Pairwise comparisons indicated that: 1) the mean melanopsin-mediated PLR was significantly reduced in all diabetic groups; 2) the mean rod-mediated PLR was reduced significantly only in the moderate-severe NPDR group; 3) the mean cone-mediated PLR was reduced significantly in the mild and moderate-severe NPDR groups. Approximately 1/4 of the patients in the mild and moderate-severe groups had normal baseline pupil diameters and reduced melanopsin- and cone-mediated PLRs, emphasizing the value of recording the PLR in addition to baseline pupil size.
Conclusions :
The observed PLR reductions in NPDR patients indicate compromised neural function. PLR measurement, particularly under the melanopsin-mediated condition, may provide a useful functional measure in patients who have NPDR, possibly capable of quantifying sub-clinical neural abnormalities in these patients.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.