The effect of under and over refractive correction on visual performance and spectacle lens acceptance

As a follow-on from a previous study by Miller, Kris and Griffiths (1997, Optom. Vis. Sci. 84, 521-526), we investigated the effect of small prescription errors on spatial visual performance and spectacle lens acceptability. We included both negative and positive errors and binocular and monocular errors. Data were collected on 15 young adult subjects. Clinical measures were taken of pupil size, ocular dominance, binocular visual acuity, negative and positive relative accommodation, distance and near heterophorias, and stereopsis. Visual performance was measured with the best correction and for +/-0.50 D spherical binocular and monocular errors. Subjects wore spectacles, each containing a different error in turn, for 2 days and compared them with a reference pair. Following the wearing period subjects assessed the performance of the spectacles by completing a short questionnaire. The only ocular tests for which these small prescription errors had significant effects were binocular visual acuity and negative relative accommodation. No significant relationship was observed between any of the clinical test results and overall lens acceptance. Despite this, the reference pair was generally perceived as better than the test pairs containing errors, and a considerable proportion of subjects reported pairs with errors as being unacceptable. In conclusion, the questionnaire findings support the need for both accurate monocular and binocular refractions. Subjects differed in their criteria for judging lens acceptability.