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TAKE HOME MESSAGE: A novel algorithm that uses three-dimensional intraocular morphology to determine postoperative effective lens position was associated with improved predictability compared with modern theoretical formulas in a study using data from 143 eyes.
Reviewed by Joseph J.K. Ma, MD
Toronto-An algorithm using three-dimensional (3-D) intraocular morphology shows promise for improving postoperative effective lens position (pELP) predictability, and therefore the accuracy of refractive outcomes after cataract surgery, said Joseph J.K. Ma, MD.
“pELP is the most significant source of error in modern IOL power calculations,” said Dr. Ma, assistant professor of ophthalmology, University of Toronto, Ontario. “Our current paradigm for refining these formulae relies on postoperative manual refraction, which can result in a pELP error, that can range anywhere from 280 to 400 µm, depending on the consistency of the refraction and power of the IOL that is implanted.
“In our study, we used a 3-D morphology based algorithm that utilized the direct measurement of the true lens position in patients who underwent femtosecond laser assisted cataract surgery (FLACS),” Dr. Ma added. “We believe that we can achieve a mean pELP error in the range of 52 µm using direct morphology based measurements.”
In addition, both the correlation coefficient and the 95% limits of agreement between the predicted and measured mean pELP were significantly better using the 3-D algorithm than with theoretically calculated multivariate estimates of pELP. The next step is to conduct additional analyses to validate these findings, including in patients not undergoing FLACS, he noted.
Dr. Ma’s study was a retrospective analysis including data from 143 consecutive eyes evaluated intraoperatively with the integrated OCT from a femtosecond laser platform and with Scheimpflug imaging and swept-source OCT at an average of more than 5 months after surgery.
Results for pELP predictability were compared with those obtained using the Haigis formula, which uses axial length for pELP prediction, and the Olsen formula, which combines axial length with measurements of anterior chamber depth and crystalline lens thickness.
Scatter plots mapping the true lens position against the algorithm predictions showed a much tighter spread of the data using the 3-D algorithm than with either of the theoretical formulas. The correlation coefficient for the agreement between the measured and predicted pELP was significantly higher using the 3-D algorithm than with the Haigis and Olsen formulas (0.86 versus 0.58 and 0.73, respectively).
“Of note, the correlation coefficients for the two theoretical formulas are much higher than those published previously,” Dr. Ma said. “The discrepancy may be explained by use of the femtosecond laser for capsulorhexis creation in the eyes included in our study.”
The data were also analyzed using Bland Altman plots that showed superiority of the 3-D algorithm compared with the Haigis and Olsen formulas for tightening the 95% limits of agreement between predicted and actual pELPs (-0.66 versus -1.96 and -1.08, respectively).
Joseph J.K. Ma, MD
This article was adapted from a presentation by Dr. Ma during Refractive Surgery Subspecialty Day at the 2015 meeting of the American Academy of Ophthalmology. Dr. Ma is a consultant and lecturer for Alcon Laboratories and Abbott Medical Optics and a consultant to Bausch + Lomb.