Printed in Great Britain CONTACT LENSES: DO THEY REALLY CHANGE THE OPTICAL PERFORMANCE?

Abstract-- In this investigation the quality of two types of optical correction, hydrogel contact lenses and ophthalmic lenses, was compared by measuring the modulation transfer function (MTF) of the correcting lens plus visual optics system using an objective method. A merit function was defined in order to allow the direct comparison between the optical performance with the two corrections. A study on 10 subjects was undertaken, measuring the MTF of both corrections by using the double pass method. The results how that the optical quality of contact lenses was higher than that with ophthalmic lenses. The contrast sensitivity function (CSF) and visual acuity (VA) were determined as subjective parameters of visuaI performance. KEY WORDS: double pass method, image quality, contact lenses, ophthalmic lenses I n t roduct ion T heoretically, the retinal images given by two dif- ferent corrections, ophthalmic lenses and contact lenses, can be compared by studying the size of the defocus circle that is produced with each correction. A subject with a refraction K, is considered. The cor-rection with ophthalmic (spectacle) lenses is1: K FSL---- (1