Residual astigmatism calculation method in implantation of a monofocal non-toric intraocular lens

Abstract

BACKGROUND: Nowadays, phacoemulsification with monofocal non-toric intraocular lens (IOL) implantation is a most common procedure in cataract surgery. Residual astigmatism has an important impact on uncorrected visual acuity. Therefore, development of residual astigmatism assessment method is relevant and may expand indications for toric IOL implantation.

AIM: To develop a method for calculating residual astigmatism in cases when non-toric monofocal IOL is implanted.

MATERIALS AND METHODS: The study included 351 patients (391 eyes, 105 men and 246 women, mean age 75.3 ± 8.5 years) who underwent phacoemulsification with non-toric monofocal IOL implantation. Biometry was performed by IOL-Master 500, postoperative refraction was assessed by autorefractometer Topcon-8800.

RESULTS: Using regression analysis, where the depended variable was residual astigmatism, and preoperative corneal astigmatism and steep corneal meridian axis location served as covariates, we revealed a significant relation (p < 0.001) with medium strength (R² = 0.51) between these parameters, which formed residual astigmatism calculation formula for monofocal non-toric IOL implantation: Ast = K_Ast · 0.71 – 0.62 · sinK_ax + 0.73.

CONCLUSIONS: This formula may allow to evaluate the residual astigmatism and justify a decision on the advisability of toric IOL implantation.

Keywords

phacoemulsification / astigmatism / intraocular lens (IOL) / toric IOL / IOL calculation formula / biometry / posterior corneal surface / Barrett toric calculator / Kane formula

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