Abstract
Purpose :
The choroid of the eye can rapidly change its thickness in response to retinal image defocus. This choroidal thickness change occurs in a predictable direction, but the mechanism is unclear. One proposed mechanism is via changes in choroidal perfusion. This study investigated the short-term effect of imposed myopic defocus on blood perfusion in the human choroid using arterial spin labelling (ASL) MRI.
Methods :
Thirty young healthy adults (12 male, age: 25 ± 4 years) were scanned by 3T SKYRA MRI after viewing a distant target (video) for 40 minutes in a supine position in a ‘mock’ scanner on two randomised visits (within a week). On one visit (experimental visit), one randomly chosen experimental eye received +2.00D myopic defocus while the fellow control eye received no defocus. At the other visit (control visit), both eyes of the subjects were optimally corrected for the viewing distance. Choroidal blood perfusion was imaged using a 3D pseudo-continuous ASL technique with turbo-gradient-spin-echo acquisition and background suppression, and analysed using Functional MRI of the Brain Software Library tools and MATLAB. Physiological parameters, such as blood pressure (BP), pulse rate, and oxygen saturation (SpO2) were also recorded during the perfusion scans.
Results :
Baseline measures of perfusion under no imposed defocus were not significantly different between the control and the experimental eye (median, 64.2 vs 62.3 ml/100ml/min, median difference (MD) = 0.05, Wilcoxon p = 0.95). No significant changes in perfusion were observed for the control eye (MD = -6.95, p = 0.15) and the experimental eye (MD = -2.32, p = 0.20) between the visits (i.e. experimental - control visit). Changes in perfusion between the visits were also not different between the control and the experimental eye (MD = -1.69, p = 0.69). Potential confounders including systolic (F(1, 27) = 0.80, p = 0.38), diastolic BP (F(1, 27) = 2.27, p = 0.14), pulse rate (F(1, 27) = 1.62, p = 0.21), and SpO2 (F(1, 27) = 0.24, p = 0.63) were not different between the visits.
Conclusions :
Short-term imposed myopic retinal defocus did not affect choroidal blood perfusion measured with ASL-MRI. Our results suggest that changes in perfusion may not be responsible for the changes in choroidal thickness seen during imposed optical defocus. Further investigations are needed to understand the mechanisms behind the choroidal thickness responses to retinal defocus.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.