Specific formulae benefit patients with keratoconus who receive toric IOLs
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Patients with keratoconus and relatively regular astigmatism can benefit from toric IOLs, provided that keratoconus-specific formulae are used for lens power calculation, according to a speaker.
“Our results showed that the Barrett True-K formula provided the most accurate IOL power,” Ehud Assia, MD, said at the European Society of Cataract and Refractive Surgeons meeting.
Calculation of IOL power in patients with keratoconus is challenging and may lead to inaccurate effective lens position and consequently inaccurate corneal power estimation, typically erring on the hyperopic side. Keratoconus-specific formulae were recently developed and include Holladay 2 and Kane, as well as Barrett True-K, a family of formulae aimed to calculate the IOL power in cases with unusual corneas, such as post-refractive surgery and keratoconus.
“Keratoconus formulae utilize specific strategies. Holladay utilizes a double-K method, Kane some modification of the corneal power, and Barrett utilizes the posterior corneal power, either measured or predicted,” Assia said.
In a study, 10 conventional formulae and keratoconus-adjusted formulae were compared in 32 eyes of 23 patients with keratoconus who underwent cataract surgery with toric IOL implantation. All patients had stable keratoconus grade 1 or 2 with relatively regular corneal astigmatism.
Outcomes were excellent overall, with more than 90% of patients achieving 20/40 or better visual acuity. Refraction was on average –5 D before surgery and almost plano after surgery. Mean corneal astigmatism was reduced from 3 D to less than 1 D. However, looking at the two groups, significantly better outcomes were seen when keratoconus-specific formulae were used.
“If we look at the mean standard deviation in predicted refraction, we see that conventional formulae often lead to hyperopia. Best results were obtained using the True-K Barrett formulae, either the predicted or the measured, followed by the Kane keratoconus formula. These results were statistically highly significant,” Assia said.
Similarly, Barrett True-K produced the best outcomes for mean absolute error and refraction accuracy, with 87.5% of the patients within less than 0.5 D of intended correction.
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Assia E, et al. Toric intraocular lens power calculation in keratoconus. Presented at: European Society of Cataract and Refractive Surgeons meeting; Oct. 8-11, 2021; Amsterdam.
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