Measurement of angle kappa and centration in refractive surgery

Abstract

Consideration of angle kappa is important for correct centration of refractive treatments. Decentered refractive treatment can cause photic phenomena including glare, halo, and deterioration of vision. This review highlights the concept of angle kappa, its measurement and distribution in normal populations, and the methods to compensate for large angle kappa in refractive surgery using laser or intraocular lenses (IOLs). Determination of the treatment center is very important in refractive surgery. Moving the ablation center from the center of the entrance pupil to points near visual axis, such as the corneal light reflex (line of sight) or corneal vertex normal, results in less induction of higher order aberrations (including coma aberration) and either the same or better visual outcomes both in hyperopic and myopic eyes when compared to laser ablation centered on the entrance pupil. Decentration of multifocal IOLs can result in deterioration of postoperative visual function with induction of higher order aberrations. The occurrence of photic phenomena positively correlated with preoperative values of angle kappa. There is a growing body of evidence that emphasizes the consideration of angle kappa in refractive surgery. Ignoring angle kappa may sometimes result in decentered treatment and aggravation of visual symptoms. Compensation for angle kappa is important for optimal correction of refractive error by either laser ablation or IOLs, especially for hyperopes and any eyes with large angle kappa.