The relationship between angle kappa and astigmatism after phacoemulsification with implanting of spherical and aspheric intraocular lens

Abstract

Purpose: To determine the significance of any association between either change in angle kappa (K°) or the rectilinear displacement ( L , mm) of the first Purkinje image relative to the pupil center and unexpected changes in astigmatism after phacoemulsification. Methods: Orbscan II (Bausch and Lomb) measurements were taken at 1, 2, and 3 months after unremarkable phacoemulsification in patients implanted with spherical (group 1, SA60AT, Alcon) or aspheric (group 2, SN60WF, Alcon) nontoric IOLs. The outputs were used to calculate L . Astigmatism, measured by autorefractometry and subjective refraction, was subjected to vector analysis (polar and cartesian formats) to determine the actual change induced over the periods 1–2 and 2–3 months postop. Results: Chief findings were that the mean ( n , ±SD, 95%CI) values for L over each period were as follows: Group 1, 0.407 (38, ±0.340, 0.299–0.521), 0.315 (23, ±0.184, 0.335–0.485); Group 2, 0.442 (45, ±0.423, 0.308–0.577), 0.372 (26, ±0.244, 0.335–0.485). Differences between groups were not significant. There was a significant linear relationship between (A) the change in K (ΔK = value at 1 month-value at 2 months) and K at 1 month ( x ), where ΔK =0.668-3.794X ( r = 0.812, n = 38, P = <0.001) in group 1 and ΔK = 0.263 x -1.462 ( r = 0.494, n = 45, P = 0.002) in group 2, (B) L and the J 45 vector describing the actual change in astigmatism between 1 and 2 months in group 2, where J 45 (by autorefractometry) =0.287 L -0.160 ( r = 0.487, n = 38, P = 0.001) and J 45 (by subjective refraction) =0.281 L -0.102 ( r = 0.490, n = 38, P = 0.002), and (C) J 45 and ΔK between 2 and 3 months in group 2, where J 45 (by subjective refraction) =0.086ΔK-0.063 ( r = 0.378, n = 26, P = 0.020). Conclusion: Changes in the location of the first Purkinje image relative to the pupil center after phacoemulsification contributes to changes in refractive astigmatism. However, the relationship between the induced change in astigmatism resulting from a change in L is not straightforward.

Measurement of change in angle kappa and its correlation with ocular biometric parameters pre- and post-phacoemulsification

“…[ 30 ] Another recent study by Tutchenko et al . [ 29 ] also observed a change in angle kappa following phacoemulsification. However, they could neither explain the cause of this change nor a way to predict this change preoperatively.…”

“…Most of the studies done previously utilized various methods for the measurement of angle kappa,[ 1 , 2 , 8 , 11 – 14 , 17 , 22 – 29 ] and though a change in angle kappa has been suggested post diffractive trifocal IOL implantation,[ 30 ] post photorefractive keratectomy,[ 27 ] post phacoemulsification[ 29 ] and with postural changes in LASIK,[ 8 ] existing literature suggests that a synoptophore,[ 17 ] as used in our study, continues to be the most accurate instrument for the measurement of angle kappa. [ 17 ]…”

Measurement of the distance between corneal apex and pupil center in patients following small-incision lenticule extraction or implantable collamer lens implantation and its correlation with the surgical-induced astigmatism

“…The correlation between SIA and change in the magnitude of chord u found in this study suggests that a reduction in refractive astigmatism following refractive surgery could have an impact on the relative locations of the corneal apex and pupil center. Tutchenko et al found that changes in the location of the first Purkinje image relative to the pupil center after phacoemulsification correlated to changes in refractive astigmatism (the J 45 vector), especially when the IOL is aspheric [ 17 ]. Although no studies exist on the relationship between angle kappa and visual function after ICL implantation, the change in angle kappa apart from ICL tilt or decentration could be one of the causes of photostress after ICL implantation [ 18 , 19 ].…”