Evaluation of contact lenses for central vision in high myopia.

Contact lenses do not significantly improve central vision as compared to spectacle lenses. I have never rehabilitated a highly myopic patient with subnormal vision by prescribing contact lenses as an optical aid, nor have I ever seen a patient so rehabilitated. My clinical experience confirms theoretical calculations that the effective magnification is not greater than 27 per cent. for a spectacle correction of -20 D. This study presents data supporting this statement based upon my own clinical tests. I suspect that what are believed to be dramatic improvements made by contact lenses can in many cases be attributed to an incorrect spectacle correction or to inaccurate vision testing. In I958, I was enthusiastic about the use of contact lenses for improving the vision of patients with subnormal vision associated with high myopia, because at that time I believed that there was a 25 per cent. increase in magnification for every Io D of myopia with the spectacle correction. I became disenchanted by my clinical experience since I could never obtain this degree of improvement. Later, a better understanding of the theory convinced me that I should not expect so great a degree of magnification. The graph published by Boeder (I938) showing a magnification of 46 per cent. for a -20 D myope has been misinterpreted to refer to the spectacle correction. At a vertex distance of 12 mm. from the cornea the spectacle correction corresponding to -20 D on the cornea is 26-25 D, and it is to this that the 46 per cent. magnification refers. Boeder's figures do not represent a comparison between contact lenses and spectacle lenses but give the retinal image size in the myope corrected with a contact lens as compared with that of the standard emmetropic eye.