The optical transverse chromatic aberration on the fovea of the human eye

The horizontal component of optical transverse chromatic aberration (TCA) at the fovea between 486 and 656 nm is measured in a sample of 8 eyes by two novel methods, both using vernier adjustment tasks with a retinal illumination of approx. 780 td and for a pupil size of approximately 5.5 mm dia. Initially, in an indirect method, TCA is derived along the line of sight from chromatic parallax. Secondly, TCA is measured directly using a semi-Maxwellian view and compensating for longitudinal chromatic aberration (LCA). Both techniques are unaffected by coma or by the Stiles-Crawford effects, thus optical TCA rather than the TCA perceived in normal view is measured. On average, optical TCA is in the same direction but less than previously predicted by eye models and predictions of the optical quality of the eye in white light are modified. Factors underlying the lower average value of optical TCA and variability among subjects, especially pupil centration and foveal position, are discussed. The relationship of optical TCA to TCA perceived in normal view and to chromostereopsis is analysed. The results suggest that the optical design of the human eye is optimized to reduce the wavelength dependent phase shift in the optical transfer function, which could be produced by optical TCA.