Effect of soft contact lenses on optical measurements of axial length and keratometry for biometry in eyes with corneal irregularities.

PURPOSE To assess the repeatability and reliability of IOLMaster (Carl Zeiss Meditec, Inc., Dublin, CA) axial length and keratometry measurements (K readings) with a soft contact lens on normal eyes. The method is designed for eyes with corneal irregularities or after endothelial keratoplasty. METHODS Biometry was performed on 20 healthy right eyes of volunteer subjects with mean age, 27.3 +/- 4.9 years; axial length, 24.77 +/- 1.04 mm; and K reading, 43.48 +/- 1.69 D. Axial length and keratometry were measured and repeated with -0.5 D SofLens38 (Bausch & Lomb, Rochester, NY) and Acuvue2 (Johnson & Johnson, New Brunswick, NJ) soft contact lenses. Repeatability and reliability were evaluated. Contact lens thickness was measured directly by corneal optical coherence tomography (OCT). RESULTS Axial lengths increased 59 +/- 10 microm with SofLens38 and 134 +/- 13 microm with Acuvue2, and these changes correlated with the OCT contact lens thicknesses (P = 0.995). The axial length variability remained constant (P = 0.18), measuring 24 +/- 10 microm for SofLens38 and 23 +/- 8 microm for Acuvue2 compared with 20 +/- 7 microm with no lens. K readings of 43.08 +/- 1.66 D with SofLens38, 42.79 +/- 1.57 D with Acuvue2, and 43.48 +/- 1.69 D with no lens corresponded to differences of -0.40 +/- 0.12 D with SofLens38 and -0.69 +/- 0.19 D with Acuvue2. The K-reading variability increased slightly from 0.04 to 0.09 D with either lens. CONCLUSIONS Low-power soft contact lenses enable reliable and repeatable IOLMaster axial length and K-reading measurements. Correcting for the measurable lens thickness and lens effects, a <0.5-D error in the Sanders-Retzlaff-Kraff (SRK) II power formula is predicted.