Angle Kappa and its importance in refractive surgery.

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.