COMMENTARY

Hitting the Effective Lens Position Target in Cataract Surgery

Sumit (Sam) Garg, MD

Disclosures

October 24, 2019

Our ability to predict intraocular lens (IOL) power has improved dramatically with modern biometry, which has increased efficiency and accuracy. Coupled with newer formulas, we now have better predictability with respect to refractive outcomes for the majority of our patients undergoing cataract surgery. Unfortunately, surgeons still experience calculation errors (> 0.5 diopters) in approximately 20% of eyes. When the refractive outcomes are off, sometimes the reason is obvious, but often, clinicians cannot trace the source of the error. Many chalk this up to inability to predict effective lens position.

A recent study[1] offers valuable insights into how we can correctly target the second eye of a patient who had a refractive miss on the first eye.

The investigators reviewed two cohorts of patients who had delayed (> 4 weeks) sequential cataract surgery and calculated the prediction error, or the difference between the predicted refractive outcome and the actual refractive outcome.

They then evaluated two methods for second eye refinement: formula-specific and patient-specific. Interestingly, they retrospectively applied both methods of refinement to each cohort to validate the refinement recommendations. They found that second eye refinement did in fact improve refractive predictability when using either of their tested methods. Of note, this refinement was for eyes that were similar in biometric characteristics (eg, axial length, keratometry), in the absence of obvious IOL tilt/decentration errors in biometry, and refractive stability was obtained at least 4 weeks after cataract surgery.

Every surgeon has a fudge factor to try and compensate for IOL power calculation errors when addressing a sequential eye. Often, however, errors in the initial surgery may not be recognized because sequential surgery is performed before refractive stability is assured. In this study, the investigators purposefully waited at least 4 weeks before proceeding with cataract surgery in the fellow eye. Although they showed an improvement in refractive predictability for the second eye, they did not report whether patients accepted this long interval between surgeries.

In addition, the Barrett Universal II (BUII) formula was found to be the most accurate in terms of prediction error compared with the other formulas studied: Hoffer Q, Holladay I, and SRK/T. The correction factor was 30% for the BUII, compared with 50% for these other formulas. This correlates with what I have seen in my own practice. The newest-generation formulas have proven to be more accurate across a larger range of eyes.

Despite our best efforts, errors still do arise. I am hopeful that applying the learnings from this study helps us improve refractive outcomes in the second eye when the first eye has an unexpected prediction error. I am even more hopeful that continued work in our diagnostic testing and biometry ultimately allows us to achieve LASIK-like predictability in our cataract refractive surgery outcomes.

Sumit (Sam) Garg, MD, is the vice chair of clinical ophthalmology and an associate professor in the Department of Ophthalmology at the Gavin Herbert Eye Institute, University of California, in Irvine. He specializes in corneal and cataract surgery, as well as laser refractive surgery.

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