Keratometry in Epikeratophakia

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Abstract
In keratomileusis and radial keratotomy, keratometry does not accurately reflect the change in refraction produced by the surgery. The authors report that this also occurs in patients undergoing epikeratophakia. The keratometer underestimates the clinically observed changes in refractive error, and changes in keratometry correlate poorly with changes in refraction. The reason for this lies partly in the method by which the keratometer estimates corneal refractive power. The authors attempted to improve the correlation between keratometry and refractive error by applying mathematical corrections to the keratometer measurements. The accuracy of these corrections was examined in three groups of patients who underwent epikeratophakia procedures: aphakic children, aphakic adults, and myopic adults. One correction, ΔD 1 , improved the estimation of change in refractive error in all three groups, while another, ΔDc, did so for two of the three groups. Neither correction significantly improved the correlation between the change in keratometry and the change in refractive error. The persistently poor correlation may be related to the irregularity of the corneal surface, the limited area of measurement by the keratometer, changes in refractive index, and changes in posterior corneal curvature. In addition, errors may occur in adjustment for vertex distance, or performing and recording measurements.

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