This study was conducted to evaluate the long-term effects of soft contact lens extended wear on visual function as measured by contrast sensitivity . Contrast sensitivity measurements were taken at 6 spatial frequencies on 39 subjects when corrected with spectacle lenses and extended wear so f t lenses . The three types of contact lenses used (CS I-T, Hydrocurve II-55, Permaflex) represented low (38%), medium (55%), and high (74%) water content s . Measured amounts of residual refractive error were corrected using a trial frame and lenses and a Clason slide and projector was used to obtain a more precise determination of Snellen acuity. All subjects had vision correctable to 20/20 or better. Data were taken on nine occasions during a five month period to investigate the effect of time upon contrast sensitivity. Two way analysis of variance for repeated measures revealed statistically significant decreases in contrast sensitivity at several of the spatial frequencies tested, or all three lens types used. Although a combined effect of the cornea and the contact lens was present in some cases, the chief cause for this decrease was the cornea.
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