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IOL calculations in post-LASIK eyes pose numerous challenges

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SAN FRANCISCO — Thorough assessment and patient counseling are critical to making accurate IOL power calculations in eyes that previously underwent myopic LASIK, a speaker said here.

During Cornea Day, which preceded the American Society of Cataract and Refractive Surgery meeting, Sumit Garg, MD, explained the various factors that can complicate IOL calculations in post-LASIK eyes.

"The first question is, ‘Why is calculation difficult?’ It really comes down to the cornea," Garg said. "In these patients, we have altered asphericity. The standard keratometry measurements that we measure miss the central cornea, where the action is. In myopic LASIK, you have flattening of the central cornea. Our current methods of measuring this miss that, so we have to assume the central power."

LASIK also increases spherical aberration; a negative spherical IOL, such as the Tecnis IOL (Abbott Medical Optics) or AcrySof IQ (Alcon), may be used in these cases, Garg said.

Approaches to making IOL calculations in post-LASIK eyes include the historical method, contact lens over-refraction, effective refractive power from Holladay diagnostic computerized videokeratography maps, refraction-derived methods, correction factors, regression formulas, nomograms and websites.

"But there’s no single proven method," Garg said. "Each physician has their own comfort zone for these things."

If using the historical method, the surgeon should use refractive values taken a few months after successful laser refractive surgery, Garg said.

Additionally, in post-LASIK eyes, the surgeon should aim for a slight myopic overcorrection of 0.5 D to 1 D.

Available tools to ensure accurate IOL calculations include the Haigis-L and Holladay II formulas, the online ASCRS calculator and intraoperative aberrometry devices, such as the ORA system (WaveTec Vision), Garg said.

Disclosure: Garg has no relevant financial disclosures.