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  • Comparison of IOL power calculations for low myopia in monovision

    Cataract/Anterior Segment, Refractive Mgmt/Intervention

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    Review of: Accuracy of intraocular lens power calculation methods when targeting low myopia in monovision

    Turnbull A, Hill W, Barrett G. Journal of Cataract & Refractive Surgery, June 2020

    This retrospective study compared the accuracy of IOL power calculation methods for myopic refractive targets.

    Study design

    Researchers examined 88 patients with a target of plano in one eye (distance eye) and -1.25 D in the other (near eye). Patients were routinely offered monovision if the distance eye achieved UDVA of 20/25 or better and the second eye had similar visual potential. The postoperative and predicted refractions were compared using the Barrett Universal II, Hill-RBF 2.0, Haigis, Holladay 1, SRK/T and Hoffer Q formulas. Because the comparison was between accuracy of the distance and near eye, the patients' eyes were paired, with the main outcome measure being accuracy for the distance versus near eye.

    Outcomes

    The accuracy of the formulas was better for the distance eye than for the near eye. The Barrett Universal II performed best, with only 1 more distance eye being within 0.5 D of target than near eye (88% vs. 86%). The Hill-RBF 2.0 was second best, with 4 more eyes in the distance subgroup achieving the target range (86 vs. 82%), while the Haigis and SRK/T formulas were most affected, with 14 (85% vs. 69%) and 11 (83% vs. 71%) more distance eyes, respectively.

    Limitations

    This was a small, retrospective study with 88 eyes that looked at some, but not all, modern formulas. Biometry was not discussed, so it is difficult to assess the applicability of these results to general practice. The entry criteria required that the first eye be successfully close to plano because monovision is not offered unless the first eye has UDVA of 20/25 or better. The order in which this practice performs surgery may have been a source of bias because entry criteria based on successful near vision performance may have provided different results.

    Clinical significance

    It is generally believed that IOL formulas are not as accurate for near targets as for plano. This paper is one of the first to assess this observation and provides support for it. Given the importance of refractive predictability in modern cataract surgery, this paper highlights the importance of IOL formula choice and the need for additional research to determine the best way to select an IOL for a myopic target.