The perceptual effects of low-power plus lenses: studies of emmetropic observers

Two studies of the perceptual effects of low-power plus lenses were done on groups of young-adult binocular emmetropic observers. The first study used visual masking to induce short-term perceptual stress in two groups of 10 observers: one group wore plano lenses and the other wore +0.50 D lenses. No significant differences in visual perceptual performance were found between these groups. The second study used a more natural letter-search task and rotated 18 observers through nine lens powers from plano to +1.0 D in +0.12D steps, to form a test of the hypothesis that "critical" lens power benefits individual observers. Other conditions in the study were arranged to maximize the positive effect of short-term wear of plus lenses, if one was found. Results showed neither an overall group benefit from a particular power of plus lens nor an individual lens power that benefited each individual observer. These data showed a strong practice effect over the nine experimental sessions, regardless of lens power, that could account for earlier reports in the literature of positive results from using these lenses.