Abstract
Purpose :
It is well known that the sub-foveal choroidal layer responds to defocused blur images with bidirectional thickness alteration. Unlike the defocus-dominated foveal region, peripheral ocular optics are largely affected by astigmatism and other complex higher-order aberrations that cause apparent directional optical blur. The goal of the study is to measure time-course changes in the peripheral choroidal response to vertical and horizontal directional blur induced by astigmatism, and positive and negative defocus.
Methods :
The temporal 15° retina was exposed for 30 min with a video stimulus (±4° horizontal & ±3° vertical visual field), providing a wide range of time-varying spatial frequency and contrast without exposing the foveal region. We used a custom-built adaptive optics (AO) visual simulator to induce ±2DCyl X 90° or ±2DCyl X 180° while correcting peripheral native ocular aberrations in real time. Depending on the axis, these astigmatic conditions introduced directional blur either in the vertical or horizontal meridian. During the exposure phase, the OCT scans were obtained in the right eyes of four emmetropic subjects (under cycloplegia) using Heidelberg Spectralis OCT at 0, 10, 20, & 30 minutes. The choroidal thickness (ChT) was automatically segmented with a MATLAB program using a deep learning neural network trained on DeepLabV3+ based on Resnet-50 (trained using 7676 images).
Results :
On average, the vertically oriented blur conditions showed higher choroidal response compared to the horizontally oriented blur conditions. Induced myopic vertical blur (+2DCyl X 180°) condition showed increased ChT from baseline (Avg ± SEM: 7.13 ± 4.39 µm; 4.13 ± 4.36, and 3.88 ± 6.64 µm at 10, 20, & 30 min respectively). Whereas choroidal thinning was observed with induced hyperopic vertical blur (-2DCyl X 180°) condition (Avg ± SEM: -2.61 ± 4.67 µm; 0.20 ± 4.84, and -3.78 ± 4.32 µm at 10, 20, & 30 min respectively). Interestingly across the exposure phase, horizontally oriented blur conditions did not show any clear trend of average ChT alteration from baseline data (average change: 0.83µm and 0.41µm for induced +2DCyl and -2DCyl at 90°, respectively).
Conclusions :
With the small sample size, we observed a bi-directional choroidal response only to vertically oriented blur induced by positive and negative defocus. This finding suggests that the peripheral choroid is selectively sensitive to directional blur signals.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.