The importance of angle kappa evaluation for implantation of diffractive multifocal intra‐ocular lenses using pseudophakic eye model

Abstract

ABSTRACT.Purpose: To determine the critical value of the angle kappa in connection with a higher risk of photic phenomena for the AcrySof ReSTOR and Tecnis multifocal intra-ocular lens (MIOL) on a standardized pseudophakic eye model. To analyse the impact of biometric value changes on the critical angle kappa. Methods: Geometrical optic rules applied to a suitable optical model of the pseudophakic eye were used to calculate the critical value of the angle kappa for the Tecnis and three types of the AcrySof ReSTOR MIOLs. The angle kappa was defined as critical if the incident ray passed through the first ring's edge area. The influence of different positive optical corneal power (K), effective lens position (ELP) and axial length (AL) on the critical angle kappa (j c ) was investigated. The dependence of j c on one of the parameters was studied for standardized values of the remaining parameters. Results: The highest value of the critical angle kappa was evaluated for the Tecnis MIOL. The increase in ELP and K caused an increase in j c under the given conditions. On the contrary, an increase in AL led to lower values of j c . Conclusion: We demonstrated the dependence of the critical angle kappa on the central part of the MIOL and on biometric parameters of the eye, especially on the effective lens position. According to these results, we conclude that shallow anterior chamber depth in connection with a higher angle kappa is an important risk factor for pronounced photic phenomena after implantation of a diffractive MIOL.

Biometric Factors Associated with the Visual Performance of a High Addition Multifocal Intraocular Lens

“…Prakash et al 3 confirm if this range of temporal decentration increases or not the risk of the symptoms as has been hypothesized. 35 We aware that our methodology for evaluating IOL centration has some important limitations in order to precisely measure the centration. The centration was based on a subjective ordinal scale interpretation and the size of the first ring at the corneal plane was assumed to be 1.2 mm.…”

Estimation of angle kappa and pupil barycentre configuration in myopic tilted disc syndrome

“…At this point, angle kappa has great importance to understand and use the optical principles involved with these complications . Studies have revealed that if angle kappa is large (≥ 0.6 mm), a high percentage of subjective complaints occur regarding halos and glare even with proper centration of the intraocular lens . Therefore, evaluation of angle kappa before refractive surgery (both corneal and lenticular) has gained significant importance.…”

“…Visual axis is the line connecting the fixation point with the fovea. Each eye has a different angle kappa, usually less than five degrees …”

“…Each eye has a different angle kappa, usually less than five degrees. 1,2 Angle kappa is a clinically important entity, particularly in laser refractive surgery and multifocal intraocular lens implantation surgery. If the angle kappa is large (≥ 0.6 mm), it can lead to misalignment errors during photoablation in laser refractive surgery and lens decentration in intraocular refractive surgery which result in negative visual effects including irregular astigmatism, reduced best-corrected visual acuity, glare and halos.…”

Method of locating the visual axis objectively

“…New technologies based on small aperture corneal inlays (small disks with about 1.6‐mm inner aperture) generated a new challenge to locate an optimal position in the cornea for implanting the inlay. The sensitivity to the centration of the inlays evoked numerous speculations – from “no influence” to “critical role” . Tabernero and Artal showed, by using numerical simulations with data from real eyes, that a decentration of 0.4 mm from a previously estimated optimal point could noticeably decrease the image quality.…”