Impact of Total Corneal Astigmatism Estimated With the Abulafia-Koch Formula Versus Measured With a SS-OCT Biometer on the Refractive Outcomes of a Toric Intraocular Lens in Cataract Surgery

Abstract

Purpose: To compare the impact of total corneal astigmatism (TCA) estimated with the Abulafia-Koch formula (TCA ABU ) versus measured by Total Keratometry (TK), swept-source optical coherence tomography (OCT) coupled with telecentric keratometry (TCA TK ) on the refractive outcomes after cataract surgery with toric intraocular lens (IOL) implantation. Methods: Two hundred one eyes of 146 patients who underwent cataract surgery with toric IOL implantation (XY1AT; HOYA Corporation) were included in this single-center, retrospective study. For each eye, TCA ABU (estimated from the anterior keratometry values measured with the IOLMaster 700 [Carl Zeiss Meditec AG]) and TCA TK (measured using TK IOLMaster 700) were entered into the HOYA Toric Calculator. Patients were operated on based on TCA ABU . For each eye, centroid and mean absolute error in predicted residual astigmatism (EPA) were calculated according to TCA used (TCA ABU or TCA TK ). The cylinder power and the axis of the posterior chamber IOL were compared. Results: The mean uncorrected distance visual acuity was 0.07 ± 0.12 logMAR, the mean spherical equivalent was 0.11 ± 0.40 D, and mean residual astigmatism was 0.35 ± 0.36 D. Mean centroid EPA was 0.28 D at 132° with TCA ABU and 0.35 D at 148° with TCA TK ( P (x) < .001; P (y) < .01). Mean absolute EPA was 0.46 ± 0.32 D with TCA ABU and 0.50 ± 0.37 D with TCA TK ( P < .01). In the with-the-rule astigmatism subgroup, a deviation from the target of less than 0.50 D was achieved in 68% of eyes with TCA ABU versus 50% of eyes with TCA TK . The proposed posterior chamber IOL was different depending on the calculation methods used in 86% of cases. Conclusions: Both calculation methods showed excellent results. However, the predictability error was significantly reduced when TCA ABU was used compared to TCA TK measured with the IOLMaster 700 in the whole cohort. Finally, TCA was overestimated by TK in the with-the-rule astigmatism subgroup. [ J Refract Surg. 2023;39(3):171–179.]

Rotational stability and refractive outcomes of a new hydrophobic acrylic toric intraocular lens

“…It has been demonstrated that including posterior astigmatism in TIOL calculation improves postoperative refractive outcomes [ 28 , 29 ]. The posterior astigmatism can be addressed through nomograms for posterior astigmatism correction, such as Abulafia-Koch, Koch-Wang, Barrett, Baylor, or by directly measuring with tomographers that use Scheimpflug or OCT [ 30 , 31 ]. A recent study has shown that strictly topographic measurements may not consider back surface astigmatism appropriately, and therefore lead to inaccuracies in TIOL calculation [ 32 ].…”

“…In the past, discrepancies in the axis and power of TIOL calculations were observed when comparing measurements of total corneal astigmatism to calculations of posterior corneal astigmatism using regression formulae [ 30 , 34 , 35 ]. In our study, we employed the 4.5 mm refractive analysis of the MS39 tomographer, resulting in highly favorable postoperative refractive outcomes.…”

Online intraocular lens calculation

“…When calculating toric IOLs, including the posterior corneal astigmatism has been shown to improve refractive results [10–12], whether measured or predicted [13 ▪▪ ,14 ▪ ,15 ▪▪ ,16 ▪ ]. Surgeons should be aware of that fact, and most online formulas have already predicted posterior astigmatism included, like the Barrett, EVO, Kane, and Naeser/Savini, while others have the option to input the posterior corneal values as well (EVO and Barrett).…”