IOL power calculation for keratoconus: One-size strategy does not fit all

Take-home message: Analyses of predicted refractive outcomes using different IOL calculation formulas suggest possible strategies for increasing predictability in eyes with mild or moderate keratoconus.

 

By Cheryl Guttman Krader; Reviewed by Wayne Bowman, MD, and David T. Truong, MD

Dallas-The challenges of IOL power calculation in eyes with keratoconus were reinforced by the results of a retrospective analysis of refractive outcomes after cataract surgery in this population. The findings also provide possible insights on approaches for optimizing accuracy.

Did you know these 7 men were ophthalmologists?

The research was undertaken by David T. Truong, MD, and Wayne Bowman, MD, Department of Ophthalmology, University of Texas Southwestern Medical School, Dallas. The review included 22 eyes of 16 patients operated on from 2010 to 2014, and the mean MRSE obtained using surgeon-specific algorithms was impressive at –0.21 D. However, the range was –6.5 D to 0.65 D.

Finding the right formula

Using clinical data to calculate predicted refraction and prediction errors using five modern lens power formulas, the investigators found the best-performing option varied depending on the preoperative corneal power.

However, none of the formulas offered good predictability in eyes with a corneal power ≥50 D.

“IOL calculation is difficult in eyes with keratoconus due to the abnormal corneal curvature, because the visual axis may not pass through the steepest part of the cornea, and since assumptions made during calculations to determine the correct IOL power are not valid in eyes with keratoconus,” said Dr. Truong, a resident in the ophthalmology department. “Our review of the literature shows remarkably little guidance on this topic.

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