Abstract
Purpose :
This study aims to develop an optical tool to precisely control longitudinal chromatic aberration (LCA) in the human eye and to examine its role in detecting signs of defocus.
Methods :
A visual simulator was built using a Spatial Light Modulator (SLM) integrated with a digital micromirror device projector for displaying visual stimuli to the eye. The principle of controlling LCA is based on the fact that a diffractive phase profile has a negative Abbe number, allowing for inducing the opposite sign of LCA to that of the human eye. The SLM was used to generate diffractive profiles for 550nm wavelength. By varying the magnitude of power of the diffractive profile, precise manipulation of ocular LCA is possible. This tool was used to study the short-term (20mins) effects of natural and reversed LCA conditions on sub-foveal choroidal thickness while exposing a video stimulus with ±2D defocus. OCT scans for choroidal thickness were taken at 0, 10, and 20 mins using Heidelberg Spectralis OCT and measured with a deep learning-based automatic segmentation algorithm.
Results :
Both theoretical and experimental bench testing demonstrated a negative and linear correlation between SLM-induced LCA and diffractive optical powers for wavelengths ranging from 463 to 661 nm. Further testing involving three human participants found that individual eyes’ natural LCA of 2.00±0.25 D could be reversed, with a residual error of -0.17±0.28 D.
In a small sample (n=3), choroidal thickness displayed bi-directional changes from baseline with native LCA defocus sessions, consistent with prior reports. Myopic defocus increased thickness (mean±SEM) by 7.21±5.90 µm at 10 mins and 9.36±7.64 µm at 20 mins, while hyperopic defocus decreased it by -7.14±3.32 µm and -14.58±4.18 µm. Interestingly, the reversed LCA condition altered this trend. Induced myopic defocus reduced thickness by -5.67±9.29 µm at 10 mins and -8.71±3.03 µm at 20 mins, while hyperopic defocus led to minimal changes of -0.15±3.38 µm and -0.76±9.34 µm at the respective times.
Conclusions :
The study has demonstrated that our SLM-based visual simulator can manipulate the eye’s LCA precisely. Our preliminary results with defocused induced short-term choroidal response indicate a potential role of ocular LCA in the detection of retinal signs of defocus, and further studies on its potential significance in refractive error development are warranted.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.