Post-illumination pupil response in subjects without ocular disease

Abstract

Purpose: A sustained pupilloconstriction is often observed after the cessation of a bright visual stimulus. This post-illumination pupil response (PIPR) is produced by the intrinsically photosensitive retinal ganglion cells (ipRGCs). The present study was designed to examine the characteristics of the PIPR in a normal population without ocular disease.

Methods: Thirty-seven subjects (mean age, 48.6 years) were tested by presenting a 60 degrees, 10-second light stimulus (13 log quanta/cm(2)/s retinal irradiance) and recording pupillary responses for 50 seconds after light cessation. The light stimuli (470 [blue] and 623 [red] nm) were presented by an optical system to one eye after dilation, while the consensual pupil response of the fellow, undilated eye was recorded by infrared pupillometry.

Results: A positive PIPR was seen in all subjects tested. The population average of the PIPR for 470-nm light was 1.5 mm (SEM 0.10, P < 0.05) and the net PIPR (blue PIPR minus red PIPR) was 1.4 mm (SEM 0.09, P < 0.0001). The net PIPR correlated positively with baseline pupil diameter (P < 0.05), but not significantly with age, race, or sex (P > 0.05) in the test population.

Conclusions: All normal subjects displayed a significant PIPR for a 10-second, 470-nm light stimulus, but not a 623-nm stimulus, which is consistent with the proposed melanopsin-mediated response. In most normal individuals, the amplitude of the PIPR was substantial. This test has the potential to be used as a tool in evaluating subjects with inner retinal dysfunction or melanopsin-related disorders.

Figure 1.

The optical system used in the study. Two Fresnel lenses (10-cm diameter) were placed twice their focal length apart within an enclosure. The two LEDs (470 and 623 nm) were placed at one end of the enclosure. The subject's dilated eye was aligned at the other end, while the undilated eye was recorded by the infrared camera attached to the computer.

Figure 2.

Time trace plots of the pupillary response to the control (red) and test (blue) LEDs (n = 37). Bar, light stimulus duration. The red and blue traces depict the pupil diameter for the red and blue lights, respectively. (A) Average pupil diameter plotted against time in all subjects. (B) Maximum response for red light generated by increasing the retinal irradiance by half a log unit. Average pupil diameter plotted against time in five subjects. (C) Spectral sensitivity nomogram for melanopsin showing the expected relative PIPR sensitivity for the 470 nm (blue trace) and 623 nm (red trace) stimuli. (D) Linear regression plots for the control (red circles, R² = 0.157) and test (blue circles, R² = 0.354) with 95% confidence interval (CI; dashed lines). Baseline pupil diameters are plotted against the PIPRs (n = 37).

Figure 3.

Box plot of tertile groups with error bars. The baseline pupil diameter response to red light grouped into tertiles, 3.3 to 4.3, 4.4 to 5.4, and 5.5 to 6.5 mm, and plotted against the PIPR. Boxes indicate the mean and 1 SE; whiskers, 2 SE.

Figure 4.

Net PIPR plotted against baseline pupil diameters, with linear regression lines (solid line) and 95% CI (dashed lines). (A) Net PIPRs (R² = 0.345, P < 0.05) = −0.465 + (0.366 × baseline). (B) Net PIPR change (R² = 0.066, P > 0.05) = 14.37 + (2.566 × baseline).

Figure 5.

Correlation between baseline pupil diameter, net PIPR, and the initial pupil responses. Regression plots show linear trend lines (solid line) and 95% CI (dashed lines). (A) Initial pupil response plotted against baseline pupil diameter (R² = 0.612, P < 0.001) = 0.419 + (1.901 × initial pupil response). (B) Net PIPR plotted as a function of initial pupil response (R² = 0.033, P > 0.05) = 0.697 + (0.276 × initial pupil response). (C) Net PIPR change plotted against initial pupil response (R² = 0.018, P > 0.05) =35.0 + (−3.271 × initial pupil response). P values are for the slopes of the regression lines.

Figure 6.

Influence of age on baseline pupil and the PIPR. (A) Average baseline pupil diameter plotted against age in years (R² = 0.166, P < 0.05). (B) Net PIPR plotted as a function of age (R² = 0.04, P > 0.05). (C) Net PIPR change plotted against age (R² = 0.002, P > 0.05). P values are for the slopes of the regression lines.