In evaluating the refractive accuracy of intraocular lens (IOL) formulas for keratoconus patients, keep in mind that although some may be more accurate than others, all formulas tend to have a hyperopic surprise, a study in the American Journal of Ophthalmology suggests.

A team of researchers from the Wilmer Eye Institute and the Albert Einstein College of Medicine enrolled 73 eyes in this retrospective case series study.

They found the Barrett Universal II formula was the most accurate for mild to moderate disease, and keratometry may help avoid hyperopic outcomes.

The study compared the accuracy of Hoffer Q, SRK/T, Holladay I, Holladay II, Haigis and Barrett Universal II formulas in eyes classified by keratoconus severity.

The researchers analyzed the results of preoperative optical biometry and topography and compared them with postoperative outcomes in keratoconus eyes that had uncomplicated cataract surgery between 2014 and 2018 at a single institution.

All formulas had a positive predicted error ranging from 0.10D to 4.38D. The Barrett Universal II formula had the lowest median absolute error for stage I (0.445D) and II (0.445D), and the highest percentage of eyes with predicted error within ±0.50D for both stage I (52%) and II (50%). In stage III eyes, the Haigis formula had the lowest median predicated error (1.90D) and the highest percentage of eyes with predicted error within ±0.50D (40%).

Additionally, corneal power measured by optical biometers was higher than measurements by keratometry, the study noted. 

Wang KM, Jun AS, Ladas JG, et al. Accuracy of intraocular lens formulas in eyes with keratoconus. Am J Ophthalmol. November 23, 2019. [Epub ahead of print].