Relationship between the Eye's Refractive Cylinder and Anterior and Total Corneal Cylinder

Abstract

Purpose: To evaluate the relationships between objective refractive cylinder and anterior as well as total corneal cylinder measured with a Scheimpflug and a Purkinje analyzer.

Methods: 30 pseudophakic eyes, with spheric monofocal intraocular lenses (IOLs), of 26 patients were measured with Pentacam, Lenstar LS 900 and Topcon automated refractor (AR). Radial curvature values of anterior (Pentacam, Lenstar) and posterior (Pentacam) corneal surfaces were derived. Ray-tracing was used to determine the astigmatic aberrations Zernike Z(2,-2) and Z(2,2) within a 3-mm zone diameter in order to calculate total corneal cylinder with 1) anterior and posterior surfaces data by Pentacam and 2) anterior keratometry values by Lenstar and posterior surface data by Pentacam. The relationship between corneal and refractive cylinder was determined with linear regression analysis.

Results: Average spherical equivalent refractive error (SD, range) was -0.66 D (1.28, -4.63 to +0.75). Average (SD) median objective refractive cylinder was -0.96 diopters (D) (0.76) @ 99.2° (43.4). Average (SD) median anterior cylinder was -0.90 D (0.56) @ 96.1° (60.3) for Pentacam and -1.06D (0.55) @ 103.3° (46.4) for Lenstar. Average (SD) median total cylinder was -0.92D (0.55) @ 98.7° (46.4) for Pentacam and -1.21D (0.97) @ 101.9° (50.1) for Lenstar/Pentacam. The R² (slope) values of linear regression analysis between magnitude of corneal and refractive cylinder were 0.17 (0.30) for Pentacam anterior corneal cylinder, 0.18 (0.30) for Pentacam total corneal cylinder, 0.65 (0.92) for Lenstar cylinder, and 0.76 (1.12) for Lenstar/Pentacam total corneal cylinder. For the relationship between axis of corneal and refractive cylinder, R² (slope) was 0.22 (0.65) for Pentacam anterior surface, 0.34 (0.63) for Pentacam total corneal power, 0.64 (1.04) for Lenstar anterior cylinder, and 0.73 (0.99) for total corneal corneal cylinder with Lenstar/Pentacam.

Conclusions: The relationship between corneal cylinder and objective refractive cylinder strengthens for magnitude as well as for axis when both anterior and posterior corneal surface measurements are taken into account. In cataract surgery, posterior corneal astigmatism may thus be important to consider, especially when using toric IOLs.

Keywords: 428 astigmatism • 733 topography • 445 cataract