Take-home message: Intraoperative aberrometry aphakic and pseudophakic readings can be comparable with careful control of surgical variables. Both readings can be useful to predict postoperative manifest refraction.
By Lynda Charters, Reviewed by William F. Wiley, MD
With the members of the Baby Boomer generation fully front and center in ophthalmology practices seeking optimal vision following cataract surgery and implantation of premium IOLs, the demand for excellent outcomes is higher than ever. Ophthalmologists are relying on intraoperative aberrometry measurements to meet those demands.
Dr. Wiley“Aphakic intraoperative aberrometry measurements improve refractive results by increasing the accuracy of picking the sphere power compared to traditional biometry and uses proprietary modification of the vergence formula to help predict correct IOL placement. However, refractive surprises still occur. The aphakic measurement relies on the preoperative biometry (Ks and axial length) to determine IOL power,” said William Wiley, MD.
In contrast, he explained, pseudophakic measurements do not rely on the preoperative biometry values, and therefore have the potential to be more predictive of the postoperative results than aphakic IOL predictions. In theory, the pseudophakic measurements measure refraction with the actual lens position and not the estimation.
However, this measurement is dependent on careful control of surgical variables, such as the anterior or posterior positioning of the lens, the effect of tilt and lens position, IOP, and viscoelastic agent.
Dr. Wiley and Shamik Bafna, MD, conducted a study in which they wanted to determine the ability of pseudophakic readings to predict postoperative manifest refraction, determine the relative usefulness of pseudophakic measurements in predicting manifest refractions, and determine the value of surgical corrections on outlier readings that differ from aphakic intraoperative predictions.
In this study, they used the Optiwave Refractive Analysis (ORA) System (WaveTec Vision). They retrospectively analyzed 50 consecutive eyes that underwent cataract surgery during a 2-month period using the intraoperative aphakic and pseudophakic readings obtained and then compared these readings with each other and with the postoperative manifest refraction. They also analyzed the pseudophakic outliers to determine if immediate surgical intervention would have improved refractive outcomes, Dr. Wiley explained.
He said he likes the Optiwave system because of the instrument’s ability to refract the eye in phakic, aphakic, and pseudophakic states during cataract surgery. The system software helps in IOL power selection and recommends appropriate positioning of toric IOLs before and after implantation.
The mean refractive deviation between the intraoperative aphakic and intraoperative pseudophakic refractions was 0.21 ± 0.27 D, between the phakic and manifest refractions 0.21 ± 0.28 D, and between the pseudophakic and manifest refractions 0.18 ± 0.26 D, Dr. Wiley reported.
The investigators found that the difference between the predicted postoperative spherical equivalent based on the aphakic measurement and the pseudophakic spherical equivalent measurement was 0.5 D or less in 84% of eyes.
Regarding the refractive outliers, seven of the 50 eyes had a pseudophakic refraction that differed by more than 0.5 D from the aphakic refraction. In five (71%) of the seven eyes, the pseudophakic prediction was closer to the manifest refraction than the aphakic fraction.
“Thus,” he noted, “if acted on, the pseudophakic refraction had a 71% chance to improve the refraction but in 29%, it would worsen.”
Drs. Wiley and Bafna concluded that the intraoperative aphakic and pseudophakic aberrometry readings can be comparable with careful control of surgical variables and both can be useful for predicting postoperative manifest refractions. When the variables are controlled carefully, the pseudophakic refraction may decrease the refractive outliers but does appear to eliminate refractive outliers, such that, even with analyzing the pseudophakic prediction, outliers still occur. They emphasized the need for another prospective study.
William F. Wiley, MD
E: [email protected]
Dr. Wiley has a financial interest in WaveTec Vision.