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Error in first eye can guide decisions in IOL selection for fellow eye of patients
Intraoperative aberrometry and newer-generation IOL formulae have signifi cantly decreased error in predictions of correction, but error still occurs. It is important to use that error as information when planning fellow eye surgery.
Reviewed by Steven Naids, MD
For cataract patients who have “normal” eyes, the error between the predicted refractive correction and the actual correction can be used to help predict error for the fellow eye, and a small study has found a good correlation between prediction error in the two eyes. “Cataract surgery in today’s world is very much a refractive procedure,” said Steven Naids, MD, Advanced Vision Care in Los Angeles.
“Achieving predictable and reproducible outcomes is very important.” Dr. Naids and colleagues tested the hypothesis that error in the first eye can guide decisions in IOL selection for the fellow eye. They compared predictive error, the difference between the manifest spherical equivalent and the predicted spherical equivalent, across multiple formulae and discussed whether predictive error in the first eye can help determine the correction needed in the fellow eye.
“Intraoperative aberrometry and newer-generation IOL formulae have significantly decreased error in our predictions of correction, but error still occurs,” Dr. Naids said. “It is important to use that error as information when planning fellow eye surgery.” The retrospective study looked at 196 eyes of 98 cataract patients with average eyes and uncomplicated phacoemulsification across surgeries performed by a single surgeon. All of the eyes had average axial length, 22.5 mm to 25.0 mm. Patients with prior refractive surgery or macular pathology were excluded.
The selected IOL power was determined by ORA for all patients. The predicted spherical equivalent based on the lens power as determined by ORA was retrospectively recorded for Barrett Universal II, Hill RBF, Haigis, Olsen, and Holladay I.
The cohort was subdivided into two groups: 58 patients who had a targeted refraction outside of the parameters of the original Hill RBF formula, and 40 patients evaluated with Hill RBF included. There was no significant difference in refractive error between the groups. There were numerical differences. For a plano target, Hill RBF had the lowest mean and median absolute error in the cohort of 40 patients, 0.16, followed by ORA, 0.17, and Barrett, 0.18.
In the initial cohort of 58 patients, the mean absolute error was lowest in ORA, 0.20, and Barrett, 0.26. In the combined cohort of 98 patients, the percentage of eyes within 0.50 D of predicted was highest with Hill RBF, 92.05%, followed by ORA, 91.38%. Olsen produced the lowest percentage of eyes within 0.50 D of predicted, 81.90%, with Holladay at 85.34%, and Barrett and Haigis at 87.07%.
Most of the eyes were within 0.25 D of predicted, Dr. Naids added, a clear indication that all of the current-generation formulae are effective and can be expected to produce results that are generally satisfactory to patients.
“If you are a half-diopter off, you won’t be able to read your iPhone easily and that is not satisfactory to patients today,” he said. It is not clear why the formulae failed by as much as a diopter in a few eyes.
All of the eyes had normal axial length and keratometry. None had had any prior refractive surgery. The study found a statistically significant correlation between the prediction error and both the first and second eyes using the current formulas as well as ORA when using a linear regression model. It is possible to anticipate the directional error in the first eye using the prediction error seen in the first eye to reduce the error in the second eye.
A study group of 20 patients outside the primary cohort found the predictive error in the first eye confirmed the IOL power for the second eye in 11 patients and changed the expected IOL power in six patients. Having the predictive error in the first eye did not help three. The next step is a similar study in a larger cohort to evaluate the effects of different formulae and predictive error in eyes that are more reflective of the general population and eyes that may not have standard axial length.
Steven Naids, MD
This article was adapted from Dr. Naids’ presentation at the 2018 meeting of the American Academy of Ophthalmology. Dr. Naids has no financial interests to disclose.