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The authors set out to compare the accuracy of four no-history formulas: Barrett True-K, Haigis-L, Shammas-PL, and Triple-S to calculate the intraocular lens (IOL) power in eyes with previous myopic photorefractive keratectomy or laser in situ keratomileusis, according to their axial length (AL) and analyse the relationship between the preoperative AL and the prediction errors (PEs) of the four formulas. They retrospectively analysed the results from 107 eyes of 107 patients with ALs divided into four subgroups: Group 1 with AL <26.0mm; Group 2 with 26.0mm≤ AL <28.0mm; Group 3 with 28.0mm≤ AL <30.0mm, and Group 4 with AL ≥30.0mm. Overall, the Triple-S method produced the lowest median absolute error (MedAE) of 0.45 D and was the only formula whose PE (0.04 ±0.68 D) did not show statistical difference from zero. Also, Haigis-L produced, on average, a constant and slightly myopic outcome in all subgroups. The Barrett True-K resulted in more myopic outcomes in longer eyes. Interestingly, the Haigis-L produced a remarkably mean myopic PE (0.49 ±0.72 D). The authors demonstrate that the preoperative AL is an important factor when choosing a formula. The most reliable formula for each group of AL were: Barrett True-K formula with AL <26.0mm and 26.0mm ≤ AL <28.0mm; the Triple-S method with AL 28.0-30.0mm and the Shammas-PL formula when the AL is ≥30.0mm. The authors evaluated the anterior corneal curvature only for calculation of the IOL power and did not evaluate the Wang-Koch-Maloney method as the necessary corneal topographer was not available to them.

Comparison of intraocular lens power formulas according to axial length after myopic corneal laser refractive surgery.
Whang W, Hoffer K, Kim S, et al.
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Mahmoud Ahmed

Royal Liverpool University Hospital, UK.

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