DOUBLE-PASS MEASUREMENTS OF RETINAL IMAGE QUALITY IN MONOFOCAL CONTACT-LENS WEARERS

The double-pass method is applied to determine the optical image quali ty in monofocal contact lens (CL) wearers. This is an objective non-in vasive technique that permits in vivo testing of the optical performan ce of CL wearers' eyes. Retinal image quality was measured for three s ubjects wearing two types of monofocal CLs: a rigid gas permeable (RGP ) CL and a soft contact lens (SL), for pupil diameters of 3 mm and 5 m m, Results show the importance of ocular astigmatism regarding retinal image quality, In eyes presenting corneal astigmatism, the best resul ts are obtained when wearing RGP CLs, because the lens compensates the corneal astigmatism. The modulation transfer function (MTF) is consid erably smaller when no lens or soft lenses are worn, even for small am ounts of astigmatism (0.5 D). When the astigmatism is corrected, the r etinal image quality obtained with both types of CLs and with no lens is similar. (C) 1997 The College of Optometrists. Published by Elsevie r Science Ltd.