The longitudinal chromatic aberration of the human eye, and its correction

The human eye suffers from longitudinal chromatic aberration, and this has been thought to average approximately 1.75 D between 420 and 660 nm. In many vision experiments the aberration may be a serious problem, and a number of lenses have been designed to correct it, two of which have recently been commercially available. These achromatising lenses produce an equal but opposite aberration to that of the average eye, and the power of the eye/lens combination should then be independent of wavelength. Recent measures of the eye's longitudinal aberration suggest that the average may be substantially greater than the above value, in which case lenses based on this figure should be inadequate. Using a Badal optometer we determined the far points for 20 subjects with each of the recent lenses, and without either, at nine wavelengths over the above range. Consistent with the early studies we found an average aberration of 1.82 D (SD 0.15 D). Both lenses performed as specified, and none of our subjects had over 0.48 D of residual aberration when corrected with either.