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  • The Barrett True-K keratoconus-specific formula has high prediction accuracy

    Cataract/Anterior Segment

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    Review of: Accuracy of intraocular lens calculations in eyes with keratoconus

    Vandevenne M, Webers V, Segers M, et al. Journal of Cataract & Refractive Surgery, March 2023

    Data from a multinational retrospective chart review were used to compare the accuracy of the keratoconus (KCN)-specific formulas with those of standard IOL calculation formulas.

    Study design

    Fifty-seven eyes with KCN that underwent cataract surgery were included in the study. Intraocular lens power calculations were made with the SRK/T, Kane, Barrett Universal II formulas, as well as the KCN-specific Kane and Barrett True-K formulas (with the latter available in measured and predicted posterior corneal astigmatism versions).

    Outcomes

    The KCN-specific formulas were found to perform better than the non–KCN-specific formulas, in terms of mean prediction error from zero. The highest percentage of eyes with prediction error within 0.25 and 0.5 D were noted with both versions of the Barrett True KCN formula. Both the Barrett KCN and Kane KCN formula performed better than the non-KCN versions of these formulas. Interestingly, SRK/T (an older formula), had greater accuracy than the Barrett Universal II and the regular Kane formulas, which are newer.

    Limitations

    The limitations of this study included its size (only 57 eyes) and the use of the following: both partial coherence interferometry and swept-source OCT biometry; a separate machine for posterior corneal power values; nonoptimized lens constants; and 8 different IOL platforms.

    Clinical significance

    The authors conclude that, whenever possible, KCN-specific IOL calculation formulas should be used in eyes with KCN. Using these formulas, notably the Barrett True-K, may be worth the additional time and effort of using the online calculator to get the best possible results. With the availability of total keratometry values, surgeons can use these calculators even if they do not have access to corneal tomography devices.

    Financial Disclosures: Dr. Kamran Riaz discloses financial relationships with Ambrx, ImmunoGen (Consultant/Advisor); Bausch + Lomb, CorneaGen (Lecture Fees/Speakers Bureau).