Abstract
Purpose :
Diurnal and seasonal variations in daylight have been implicated in ocular growth
(Hagen, Sci. Rep. 2018, 8(1), 1-10.; Ulaganathan, Exp. Eye Res. 2019. 189). The aim of this study was to explore the diurnal relationship between axial length and choroidal thickness in humans in winter and summer at 60° latitude North.
Methods :
Twenty-four ocular healthy participants (age 17-24 yrs, 11 males), with logMAR visual acuity ≤0.00 and stereo acuity of ≤120” were included and measured in Southern Norway during the winter (6 hours of daylight/day) and summer (18 hours of daylight/day). On day 1, an actigraph was handed out to the participants to collect habitual sleep times (HST) over a 7-day period. Individual HST and self-reported habitual wake up time were used to calculate the timing of 9 rounds of measurements on day 8. Each round consisted of accommodation washout (15 min), OCT imaging (Heidelberg Spectralis OCT2 EDI) and axial length (AL) measurements (Zeiss IOLMaster 700). The central 1 mm choroid (CT) was segmented with custom-made software using an active-contour method. A sinusoid, with a period of 24 hours, was fit to the data (AL and CT) with an non-linear mixed effects model to estimate the MESOR, amplitude and phase, and determine the seasonal effect of these parameters.
Results :
AL ranged from 21.26 to 27.53 mm and CT ranged from 90 to 659 mm. Increasing AL correlated with thinner CT in winter and summer (R2=0.42, p<0.0001, R2=0.38, p<0.0001, respectively). AL and CT underwent significant diurnal variations both in winter and summer (one-way ANOVA, p<0.0001). MESOR AL increased significantly from winter to summer (Δ0.045 mm, p<0.0001) whereas MESOR CT did not change. AL and CT acrophase was 12 hours out-of phase in winter and there was a significant acrophase advance for AL only, about 90 min earlier in the summer (p<0.05).
Conclusions :
The results show that the diurnal rhythms of AL and CT are in anti-phase in winter, but because there is no evidence for a seasonal change in the diurnal rhythm of CT between winter and summer, we find instead that there is a shift in the relationship between acrophase of AL and CT in summer related to seasonal changes of AL only.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.