Abstract
Purpose :
Human color vision is based on the spectral sensitivities of S, M, and L cone photoreceptors, yet methods to objectively measure cone sensitivity as a function of wavelength over the entire visible light spectrum in the living human eye still do not exist. Here, we demonstrate a new, high resolution method based on phase-sensitive adaptive optics optical coherence tomography (AO-OCT) for measuring spectral sensitivities of the three different cone types.
Methods :
AO-OCT volumes of 1°×0.8° at 3.8° temporal retina were acquired over 5 s for two color normal subjects. At 2.5 s, a 5 ms flash of 450 nm, 520 nm or 635 nm light with variable strength was delivered to the retina. The resulting temporal changes in the cone outer segment optical path length (ΔOPL) were extracted from the volume images and used to determine the spectral type [1] and sensitivity of each cone. Sensitivity was determined by fitting the cones’ average peak response at each wavelength to a power function of stimulus photon strength after compensating for lenticular and macular absorption. We then separately scaled the measured sensitivity function for each cone type to best align with widely accepted psychophysical measurements [2]. In both subjects, spectral sensitivity 95% confidence intervals (CI) were calculated for S, M, and L cone types at the three stimulus wavelengths by computing the average and standard deviation values of S, M and L cone average peak response per stimulus flash strength and using the resulting probability distributions to estimate the CIs via a Monte Carlo simulation.
Results :
For both subjects, CI were <6.0e-3 at all wavelengths and for all cone types (except we had insufficient response to calculate a CI for S cones at 635 nm). After aligning our data to the psychophysical results, the least-squares error across 450 nm, 520 nm, and 635 nm wavelengths for S, M, and L cones, respectively, was [5.50e-4, 2.62e-4, 2.4e-3] for Subject 1, and [1.04e-4, 3.4e-2, 1.23e-4] for Subject 2.
Conclusions :
We demonstrate the first objective measurements of cone spectral sensitivities using phase-sensitive AO-OCT. Excellent agreement is obtained with Stockman & Sharpe’s psychophysical measurements.
[1] Zhang, et al. PNAS 116.16 (2019): 7951-6.
[2] Stockman, A., & Sharpe, L. T. (2000). Vision Res. 40, 1711-1737.
This is a 2021 ARVO Annual Meeting abstract.