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August 1987

On Predicting Ocular Power Changes in Refractive Keratoplasty

Author Affiliations

Glasgow, Scotland

Arch Ophthalmol. 1987;105(8):1017. doi:10.1001/archopht.1987.01060080015003

To the Editor.  —The recent article by McCarey and colleagues1 was most thought provoking and clearly demonstrated the state of the art. However, the authors' conclusion that the polysulfone implant produces a greater refractive change on account of its high refractive index is not wholly justified. The lidofilcon-B implants (refractive index, 1.3686) used by the authors had an average power in air of +10.00 diopters (D), the polymethylmethacrylate implants (refractive index, 1.49) had an average power in air of +26.25 D, and the polysulfone implants (refractive index, 1.63) had an average power in air of +36.75 D. Taking the authors' raw data and plotting a graph of implant power in air against corresponding change in ocular power found by retinoscopy, we find a remarkable linear relationship (Figure). Application of linear regression yields the following value: y = 5.53 − 0.53x; correlation coefficient = −0.9685; y indicates change in ocular power,

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