Abstract
Purpose: :
To examine the changes in the normal diurnal rhythms of subfoveal and parafoveal choroidal thickness associated with monocular myopic defocus in young adult human eyes.
Methods: :
Diurnal choroidal thickness measures, derived from spectral domain optical coherence tomography (OCT) images (collected at ~3 hourly intervals on each day, with the first measurement at ~9 am and the final measurement at ~9 pm) were obtained for 13 emmetropic young adults (mean age 26 ± 2 years) over three consecutive days. Day 1 (baseline day, no defocus) examined the normal diurnal variations in choroidal thickness, day 2 (defocus day) investigated the influence of monocular myopic defocus on diurnal choroidal rhythms (+1.50 DS spectacle lens was worn over the right eye, for the duration of the day), and the recovery from any choroidal changes induced by defocus, were explored on day 3 (recovery day, no defocus). The OCT images from each session were manually segmented to calculate subfoveal, and parafoveal choroidal thickness (in nasal and temporal regions extending to 1.5 mm from foveal centre).
Results: :
Both subfoveal and parafoveal choroidal thickness underwent significant diurnal variation on each of the three measurement days (p<0.05). The introduction of monocular myopic defocus on day 2, resulted in significant changes in the amplitude and timing of choroidal rhythms in the right eye (p<0.01). For baseline and recovery days (no defocus), the thickest choroid was typically observed at the final measurement session (mean time 20:59pm), however on day 2, with defocus, the thickest choroid typically occurred at the second session (12:25pm). The mean amplitude (peak to trough) of choroidal change was also significantly different between days (mean amplitude of change: 30 ± 7, 22 ± 6 and 27 ± 9 µm for baseline, defocus and recovery days respectively, p=0.025). The magnitude and timing of diurnal rhythms and the influence of defocus in parafoveal choroidal thickness was similar to that observed in the subfoveal measures.
Conclusions: :
Diurnal rhythms of subfoveal choroidal thickness in human eyes are significantly disrupted by the introduction of monocular blur, but rapidly return to normal upon removal of the defocus. The parafoveal choroid also exhibits significant changes in response to defocus.
Keywords: myopia • choroid • adaptation: blur