In this study, investigators refine the refractive outcome of the second eye after cataract surgery by deriving adjustment coefficients for IOL selection based on the prediction error (PE) of the first eye.
Study design
This retrospective analysis of delayed sequential bilateral cataract surgery included 139 patients from Australia who had surgery by one surgeon and 605 patients from the United Kingdom who had surgery by multiple surgeons.
The authors compared 2 methods for second-eye refinement (i.e., formula-specific adjustment and patient-specific optimized IOL constants) to determine if the results could be reliably applied to a wider population.
In the first method, the authors used the coefficients of 4 formulas derived from the Australian group to adjust the second-eye predicted postoperative refraction (PPOR) in the U.K. group, and vice versa. In the second method, they derived a patient-specific coefficient for 2 formulas that was applied to the optimized IOL constant from the first eye to calculate the second-eye IOL power.
Outcomes
In the Australian group, the improvement in mean absolute error after second-eye refinement using the formula-specific PPOR adjustment was statistically significant for all formulas tested, and ranged from 2.6% to 11.5% depending on the formula used. Similarly, the U.K. group showed improvements of 2.0% to -4.7%; however, a nonstatistically significant improvement was noted with the Hoffer Q formula.
The second method of deriving patient-specific optimized IOL constants provided similar results, without a significant difference between the methods. The Barrett Universal II had the lowest overall mean absolute error in each subgroup and was the least likely to show an improvement with the PPOR adjustment.
Limitations
There was not a consistent comparison between the groups. The U.K. group only had axial length and K values available, rather than all parameters needed for the Barrett Universal II formula (as was available in the Australian dataset). Older generation formulas were studied rather than newer formulas such as the Olsen and Hill-RBF, and these data suggest that a PPOR adjustment is less valuable when using these formulas. Finally, as this was a retrospective study, surgeons were likely using an adjusted PPOR for the second eye given that it was the recommendation of United Kingdom National Institute for Health and Care Excellence
Clinical significance
With the availability of newer generation formulas and improved biometry, the practice of refining second eyes will likely diminish, especially as short interval cataract surgery is becoming more common worldwide. It goes without saying that optimizing a surgeon’s constants continues to be of the utmost importance. The most important lesson from this study is that surgeons should be using newer-generation formulas and abandon older generation formulas whenever possible.