Tolerance to Prism Induced by Readymade Spectacles: Setting and Using a Standard

Most spectacle wearers would likely comfortably tolerate <or=0.5 Delta vertical, <or=1.0 Delta base out, or <or=1.0 Delta base in induced prism. A guide to the maximum interpupillary distance/optical center distance disparities likely to be comfortably tolerated with varying spectacle powers was formulated. Powers up to +/-1.50 DS are unlikely to have sufficient lens decentration to cause discomfort. This small study supports the feasibility of using readymade spectacles in low-resource settings even though optical center distance may be different to the interpupillary distance of the wearer. It would seem that fear of visual discomfort because of induced prism need not preclude the use of readymade spectacles, potentially correcting about 75% of refractive error and presbyopia, mostly with powers +3.00 to -3.00 DS. Further study is needed to more fully address these issues.