Angle alpha orientation and magnitude distribution in a cataract surgery population
Michael A. Mahr, Michael J. Simpson, Jay C. Erie
Abstract
PURPOSE: To report normative angle alpha orientation and magnitude distribution in a cataract surgery patient population. SETTING: U.S. academic medical center. DESIGN: Retrospective review. METHODS: A total of 11 871 wavefront aberrometer/corneal topographer angle alpha measurements were performed over 40 months, yielding 8773 bilateral measurements (73.9%) with zero bad wavefront datapoints. The analysis was limited to the first right-eye scan for 3382 unique patients. The angle alpha magnitudes (millimeters) and orientations (degrees) were analyzed for these unique right eyes. RESULTS: For the 3,382 unique patients, the mean angle alpha magnitude was 0.44 ± 0.15 mm (median, 0.44 mm; 25th and 75th percentiles 0.34 mm, 0.53 mm). Angle alpha orientation was predominantly horizontal (P < .01), with a mean of 186 ± 32 degrees. The expected point of intraocular lens (IOL) centration (EPIC) based on the geometric center of the corneal limbus was temporal to the visual axis in 3212 eyes (95%), nasal in 92 eyes (2.7%), inferior in 56 eyes (1.7%), and superior in 22 eyes (0.6%). The mean angle alpha magnitude was 0.3 mm or less in 607 eyes (18%) and 0.5 mm or greater in 1089 eyes (32%). CONCLUSIONS: Angle alpha is a predominantly horizontal phenomenon with a mean EPIC of 0.44 mm temporal to the visual axis. This information may assist in determining eligibility for patients in multifocal IOL implantation.