Effects of Narrowband Light on Choroidal Thickness and the Pupil

Abstract

Purpose: To determine the effects of narrowband light exposure on choroidal thickness and the pupil response in humans.

Methods: Twenty subjects, ages 21 to 43 years, underwent 1 hour of exposure to broadband, short wavelength "blue," or long wavelength "red" light, or darkness. Choroidal thickness, imaged with spectral domain optical coherence tomography, axial length, determined from biometry, and rod/cone- and intrinsically photosensitive retinal ganglion cell-driven pupil responses were measured before and after exposure. Pupil stimuli were six 1 second alternating red (651 nm) and blue (456 nm) stimuli, 60 seconds apart. Pupil metrics included maximum constriction and the 6 second post-illumination pupil response (PIPR).

Results: Compared with before exposure, the choroid significantly thinned after broadband light, red light, and dark exposure (all P < 0.05), but not after blue light exposure (P = 0.39). The maximum constriction to 1 second red stimuli significantly decreased after all light exposures (all P < 0.001), but increased after dark exposure (P = 0.02), compared with before exposure. Maximum constriction and 6-second PIPR to 1 second blue stimuli significantly decreased after all light exposures compared with before exposure (all P < 0.005), with no change after dark exposure (P > 0.05). There were no differences in axial length change or 6-second PIPR to red stimuli between exposures.

Conclusions: Narrowband blue and red light exposure induced differential changes in choroidal thickness. Maximum constriction, a function of rod/cone activity, and the intrinsically photosensitive retinal ganglion cell-mediated PIPR were attenuated after all light exposures. Findings demonstrate differing effects of short-term narrowband light and dark exposure on the choroid, rod/cone activity, and intrinsically photosensitive retinal ganglion cells.

Conflict of interest statement

Disclosure: L. Lou, None; L.A. Ostrin, None

Figures

Figure 1.

(A) A six-line 30° radial scan protocol used for SD-OCT imaging. (B) Segmentation of Bruch's membrane (red) and the choroid/sclera border (blue). Choroidal thickness was averaged for a 1-mm wide region centered at the fovea. (C) Representative choroidal thickness map generated from the segmentations. Yellow areas represent thicker regions of the choroid and blue areas represent thinner regions of the choroid.

Figure 2.

(A) Experimental protocol. Subjects first underwent a 10-minute distance viewing task under 60 lux room illumination. OCT imaging, ocular biometry, and pupil measurements were conducted before and after a 1-hour exposure condition. (B) Pupil stimulation protocol. Five minutes of dark adaptation was followed by 10 seconds of baseline pupil diameter recording. Three 1-second red and three 1-second blue stimuli were presented in alternating order, with a 60-second interstimulus interval.

Figure 3.

Spectral composition and room set up for (A, B) broadband light (C, D) short wavelength blue light, and (E, F) long wavelength red light.

Figure 4.

Bland-Altman analysis of the difference between scan 1 and scan 2 against mean choroidal thickness to assess within-session repeatability. The dashed and dotted lines represent the mean difference and 95% limits of agreement, respectively. Shaded areas represent the 95% confidence intervals for the mean difference and 95% limits of agreement.

Figure 5.

Change in (A) choroidal thickness and (B) axial length after 1 hour of exposure for each condition; broadband light (open bars), blue light (blue bars), red light (red bars), and darkness (black bars). Error bars represent standard error of the mean. **P < 0.01.

Figure 6.

(A) Maximum constriction (%) and (B) 6-second PIPR (%) before (open bars) and after 1 hour of exposure (red bars) to broadband light, blue light, red light, or darkness in response to a 1-second red stimulus. (C) Maximum constriction (%) and (D) 6-second PIPR (%) before (open bars) and after 1 hour of exposure (blue bars) to broadband light, blue light, red light, or darkness in response to a 1 second blue stimulus. *P < 0.05, **P < 0.01, ***P < 0.001.