DOES THE PRESBYOPIC VISUAL-SYSTEM ADAPT TO CONTACT-LENSES

We studied whether task performance improves during the initial wearin g period of selected presbyopic contact lens corrections. In three pre vious studies significant decreases in performance on three selected t asks were measured before and after initial wearing periods to monovis ion contact lenses (N = 18, 8 weeks of wear), concentric bifocal lense s (N = 32, 8 weeks), and diffractive and monovision lenses (N = 20, 3 weeks). In each study, the control condition was distance contact lens es with reading spectacles. The decreases in performance speed ranged from 2 to 15% compared to control. In this study, we retrospectively a nalyze the data to determine whether the task performance decreases re lative to control were significantly different after the initial weari ng period than at the time of dispensing-i.e., did measures of task pe rformance show an adaptation to the presbyopic contact lens correction ? Performance adaptation on each task and for each study was analyzed statistically using the Wilcoxon matched pair signed rank test of each subject's mean performance differences (test vs. control condition) a t dispensing compared to the performance at the end of the wearing per iod. There was no improvement in task performance with monovision or d iffractive bifocal lenses. However, we found significant improvements in task performance with concentric bifocal lenses (p < 0.05). Measure s of visual acuity and stereoacuity did not improve with these lenses during the studied wearing period. Thus, these basic visual skills did not adapt. The ability of patients to learn how to use reduced visual acuity to perform complex tasks is a possible explanation for the imp roved task performance with concentric bifocal lenses compared to cont rol.