Perceptual impact of astigmatism induction in presbyopes.

We investigated the effect of induced astigmatism on subjective best focus and on visual acuity in 28 subjects of different ages (pre-presbyopic and presbyopic) and with different refractive profiles (emmetropes and astigmats). Measurements were performed using a custom-developed Adaptive Optics system, which allowed correction of high order aberrations and induction of astigmatism (0.5, 1, 1.5 and 2.0 D; axis: 180°, 45° and 22.5°). Upon induction of astigmatism, best focus shifted towards negative values in pre-presbyopic emmetropic eyes (by -0.14 D for 0.5 D and by -0.33 D for 2.0 D), while it shifted towards positive values in presbyopes, both in emmetropic presbyopes (by +0.04 D for 0.50 D and by +0.16 D for 2.0 D) and in astigmatic presbyopes (by +0.23 D for 0.50 D and by +0.40 D for 2.0 D). Also, visual acuity was most sensitive to astigmatism induction in pre-presbyopic emmetropes and least sensitive in presbyopes, particularly when high order aberrations were corrected: visual acuity ratio with/without astigmatism was: 0.74/0.85/0.98 (for astigmatism induced at 180°) and 0.68/0.73/0.86 at 45°, for pre-presbyopic emmetropes/presbyopic emmetropes/presbyopic astigmats. These findings may be connected to long term exposure to astigmatism in astigmats and corrected presbyopes.