Pseudophakic IOL power calculation still a significant challenge in postrefractive surgery

A study evaluating different methods of calculating effective corneal power in eyes with a history of corneal refractive surgery reinforce there is no ideal means to measure that value, said Helga P. Sandoval, MD, Storm Eye Institute, Medical University of South Carolina, Charleston.

"Therefore, it is important to discuss with patients preoperatively that there is an increased likelihood of needing IOL surgery exchange, piggybacking, or additional corneal surgery after the cataract procedure," Dr. Sandoval said.

Dr. Sandoval presented findings from four groups of eyes in which six different methods for calculating the effective corneal power after corneal refractive surgery were investigated. The target refractions based on actual and refraction-derived keratometric values were compared with the postoperative achieved refractions.

The four groups consisted of eyes that had undergone myopic LASIK (26 eyes), hyperopic LASIK (18 eyes), myopic PRK (4 eyes), or RK (5 eyes). In the two largest groups, the methods evaluated included the clinical history method, adjusted effective refractive power, Modified Maloney, Hill, Masket, and an eye scanner (Pentacam, Oculus).

In the myopic LASIK eyes, the effective refractive power, Masket, and Hill methods gave the most accurate results with respect to proportion of eyes within 1 D of target refraction. Using a cutoff of achieved refraction within 0.5 D of target, the Masket method performed best. For the hyperopic LASIK eyes, the Hill, Masket, effective refractive power, and historical data methods were all associated with high percentages of eyes within 1 D. For the analysis of achieved refraction within 0.5 D of target, the Hill and effective refractive power methods had the greatest accuracy.

"However, compared with eyes that have undergone myopic LASIK, determination of effective corneal power is less of a problem after hyperopic LASIK," Dr. Sandoval said.