Abstract
Purpose :
Circadian rhythms are mediated by light exposure and endogenous clocks, and have been shown to be altered in myopic eye growth. Here, we assess relationships between objectively measured light exposure with ocular and systemic diurnal rhythms in adults with emmetropia and myopia.
Methods :
Adult subjects (n=42, 22-41 yrs) with a range of refractive errors (+1.3 to -11.2 D) were recruited to wear a light, sleep and activity monitor for one week, after which a series of measurements were recorded every 4 hours (h) for 24 h. Subjects were in the dark (<1 lux) from 23 to 7 h. At each time point, blood pressure, heart rate, body temperature and intraocular pressure (IOP) were measured 3 times, and 1 ml of saliva was collected for melatonin and cortisol analysis. Mean ocular perfusion pressure (MOPP) was calculated. Ocular biometry, autorefraction and optical coherence tomography (Spectralis) images were collected (six 30° radial scans centered at the fovea). Custom software was used to determine choroidal and retinal thickness to 6mm eccentricities. For each measure, a cosine function was fitted and acrophase was determined for emmetropes and myopes.
Results :
Subjects spent an average of 92.2±7.3 (mean±SE) minutes outdoors per day over the previous week and demonstrated normal sleep patterns. Over the course of 24 h, all measures exhibited significant diurnal variation. Choroidal thickness peaked at 4 h, with a diurnal variation of 26.5±2.3 µm, in approximate anti-phase with axial length, which peaked at 12 h and had a diurnal variation 35.7±3.0 µm. Melatonin increased following light offset with a peak at 4 h, while cortisol peaked after light onset. IOP peaked at 12 h, with a diurnal variation 4.8±0.3 mmHg. MOPP peaked after light offset (24 h). Central retinal thickness demonstrated significant diurnal variation (5.1±0.3 µm) with a peak at 12 h. Mean change in AL was correlated with mean change in IOP (R2=0.78, p=0.02). There were no significant differences in the amplitude of diurnal measures between refractive error groups. However, IOP acrophase was at 8 h for myopes and 12 h for emmetropes.
Conclusions :
Diurnal variation in ocular and systemic processes were observed over 24 hours in young adults, with each function exhibiting a unique acrophase and relationship with light exposure. Rhythms were similar between emmetropes and myopes in this adult population.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.