RELATIONSHIP OF THE ACTUAL THICK INTRAOCULAR-LENS OPTIC TO THE THIN LENS EQUIVALENT

PURPOSE: To theoretically derive and empirically validate the relation ship between the actual thick intraocular lens and the thin lens equiv alent. METHODS: Included in the study were 12 consecutive adult patien ts ranging in age from 54 to 84 years (mean +/- SD, 73.5 +/- 9.4 years ) with best-corrected visual acuity better than 20/40 in each eye. Eac h patient had bilateral intraocular lens implants of the same style, p laced in the same location (bag or sulcus) by the same surgeon. Preope ratively, axial length, keratometry, refraction, and vertex distance w ere measured. Postoperatively, keratometry, refraction, vertex distanc e, and the distance from the vertex of the cornea to the anterior vert ex of the intraocular lens (AV(PC1)) were measured. Alternatively, the distance (AV(PC1)) was then back-calculated from the vergence formula used for intraocular lens power calculations. RESULTS: The average (/-SD) of the absolute difference in the two methods was 0.23 +/- 0.18 mm, which would translate to approximately 0.46 diopters. There was no statistical difference between the measured and calculated values; th e Pearson product-moment correlation coefficient from linear regressio n was 0.85 (r(2) = .72, F = 56). The average intereye difference was - 0.030 mm (SD, 0.141 mm; SEM, 0.043 mm) using the measurement method an d +0.124 mm (SD, 0.412 mm; SEM, 0.124 mm) using the calculation method . CONCLUSION: The relationship between the actual thick intraocular le ns and the thin lens equivalent has been determined theoretically and demonstrated empirically, This validation provides the manufacturer an d surgeon additional confidence and utility for lens constants used in intraocular lens power calculations. (C) 1998 Elsevier Science Inc. A ll rights reserved.