Abstract
Purpose:
The purpose of this study was to use a new image-based technique to make the first-ever objective measures of TCA at different eccentricities within the human visual field.
Methods:
TCA was measured at visual field angles of 0.5, 2.5, 5, 7.5, 10, 12.5, and 15 degrees from foveal fixation in the right eye of 4 subjects. Interleaved retinal images were taken at wavelengths 543 nm and 842 nm in an adaptive optics scanning laser ophthalmoscope (AOSLO) and were cross-correlated according to methods described in Harmening et al., Biomed Opt Express, 2012. Pupil alignment was controlled with a pupil-camera. To obtain true measures of human eye TCA, the contributions of the AOSLO system TCA were measured using an on-axis aligned model eye and subtracted from the human eye data.
Results:
The system TCA was stable at around 3 arcmin. On all subjects, it was possible to measure TCA out to 12.5 degrees in the nasal, 10 degrees in the temporal, 12.5 degrees in the inferior, and 15 degrees in the superior visual field. The absolute amount of TCA between green and IR varied somewhat between subjects, but was approximately 4 arcmin at 10 degrees out in the nasal visual field. However, the increase in TCA was found to be linear with a slope close to 0.2 arcmin / degree of visual field angle for all subjects. Translating these results to the visual spectrum would yield a slightly higher slope and larger image shifts, which agree with the theoretical calculations by Thibos, J. Opt. Soc. Am. A, 1987.
Conclusions:
We have performed the first objective measurement of the TCA of the human eye across the central 30 degrees visual field. The 4 arcmin of TCA at 10 degrees off-axis is very similar to the resolution acuity of 0.5 to 0.7 logMAR at 10 degrees out in the nasal visual field (about 3 to 5 arcmin). Additionally, the measured cone-size at 10 degrees in the subjects of this study was about 1.4 - 1.7 arcmin, which means that the TCA blur covers around 2-3 cones. Therefore, the peripheral TCA can be visually significant.