INFLUENCE OF AMOUNT AND CHANGES IN AXIS OF ASTIGMATISM ON RETINAL IMAGE QUALITY

We measured retinal image quality in astigmatic eyes, using the double -pass technique. We analyzed the influence of the amount of astigmatis m and changes in axis of astigmatism on the eye's optical performance. Different amounts of astigmatism were obtained by variation of the cy lindrical power of a lens situated in front of the eye, between 0.25-d iopter (D) overcorrection and 1-D undercorrection at intervals of 0.25 D. Changes in the axis of astigmatism were obtained by rotation of th e lens, which neutralizes the astigmatism in an angle of +/-10 degrees at 5 degrees intervals. The results show the decrease in retinal imag e quality and the increase in the degree of image astigmatism obtained when the amount of astigmatism increases or the angle between the len s and the eye axis is other than zero. In general, the largest variati ons correspond to when the astigmatism changes from 0 to 0.25 D or whe n the axis changes from 0 degrees to +/-5 degrees. The reduction in op tical performance is smaller in living eyes than in an eye model or in an artificial eye. The aberrations present in the living eye reduce t he relative loss of retinal image quality introduced by astigmatism. ( C) 1998 Optical Society of America.