Angle Kappa and its importance in refractive surgery

Abstract

Angle kappa is the difference between the pupillary and visual axis. This measurement is of paramount consideration in refractive surgery, as proper centration is required for optimal results. Angle kappa may contribute to MFIOL decentration and its resultant photic phenomena. Adjusting placement of MFIOLs for angle kappa is not supported by the literature but is likely to help reduce glare and haloes. Centering LASIK in angle kappa patients over the corneal light reflex is safe, efficacious, and recommended. Centering in-between the corneal reflex and the entrance pupil is also safe and efficacious. The literature regarding PRK in patients with an angle kappa is sparse but centering on the corneal reflex is assumed to be similar to centering LASIK on the corneal reflex. Thus, centration of MFIOLs, LASIK, and PRK should be focused on the corneal reflex for patients with a large angle kappa. More research is needed to guide surgeons’ approach to angle kappa.

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

“…32 The µ-chord, which is correlated with kappa angle, 26,33 has been hypothesized to be related with the visual performance achieved with MIOLs. 34 However, to this date, there is only one clinical study that correlates the kappa angle with the visual performance. Prakash et al 3 confirm if this range of temporal decentration increases or not the risk of the symptoms as has been hypothesized.…”

Comparison of Preoperative Angle Kappa Measurements in the Eyes of Cataract Patients Obtained from Pentacam Scheimpflug System, Optical Low-Coherence Reflectometry, and Ray-Tracing Aberrometry

“…The larger the discrepancy between the visual axis and pupillary axis or visual axis and optical axis is, which decreased the visual quality. In the MIOLs of eyes with a large angle kappa, the light might pass the center of the macula through other diffractive rings instead of the central area of the MIOLs, which is also known as functional IOL decentration [10], thereby leading to the photic phenomena and surgical aberrations [11,12]. Therefore, according to the angle kappa, adjusting the position of the MIOLs may help reduce photic phenomena [11,13].…”

“…In the MIOLs of eyes with a large angle kappa, the light might pass the center of the macula through other diffractive rings instead of the central area of the MIOLs, which is also known as functional IOL decentration [10], thereby leading to the photic phenomena and surgical aberrations [11,12]. Therefore, according to the angle kappa, adjusting the position of the MIOLs may help reduce photic phenomena [11,13]. In addition, some studies also indicated that more than 0.5 mm of preoperative angle kappa should be carefully considered in cataract patients implanted with diffractive or refractive types of MIOLs [6,11,14].…”

Automated Retinal Topographic Maps Measured With Magnetic Resonance Imaging

“…The difference between the visual axis and the pupillary axis is quantified by the angle kappa and is on the order of 58. 34,35 The current MRI methods do not provide a high enough spatial resolution either to detect the foveal pit, needed to define the visual axis, or to measure the center of the pupil and the perpendicular intersection with the cornea, needed to reconstruct the pupillary axis. Therefore a different axis is defined, which can be geometrically reconstructed from the MR images.…”