Optical performances of human eyes derived from double-pass measurements.

Point-spread functions (PSF's) of human eyes at medium pupil size (3.5 mm) were derived from double-pass measurements. It was demonstrated that reliable information on PSF shape in the central 7-arcmin radius can be obtained in spite of uncertainty about the height and extent of the tail of the double-pass image. Measurements from some healthy young eyes (of subjects 21-31 years old) and several older eyes (of subjects 63-75 years old) with good acuity revealed little difference in the half-width at half-height of the PSF, but, owing to the higher tail in their PSF's, the Strehl ratio of the older eyes is much lower. Computation of the modulation transfer functions of the older eyes revealed a more prominent loss at low spatial frequencies.