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Lens equatorial plane used to predict postop IOL position
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The crystalline lens equatorial plane was found to be a promising predictor of postoperative IOL position, according to a study.
“We believe that the use of the lens equatorial plane for IOL power calculation can be a practical choice for use in the clinic and might make it possible to improve refractive outcomes for cataract surgery,” lead study author Young-Sik Yoo, MD, told Healio.com/OSN.
In the comparative interventional case series, phacoemulsification and IOL implantation were performed in 104 eyes; lens geometry parameters, including lens equatorial plane, were obtained before surgery.
All patients underwent femtosecond laser pretreatment with the Catalys platform (Johnson & Johnson Vision) and then phacoemulsification and implantation with a single-piece plate haptic IOL without angulation: the ZCB00 (Johnson & Johnson Vision), group 1; the EC-1 PAL (Aaren Scientific), group 2; or the CT Asphina (Zeiss), group 3.
Mean preoperative anterior chamber depth measurements were 3.27 mm, 3.3 mm and 3.49 mm in groups 1, 2 and 3, respectively. Mean preoperative lens equatorial plane measurements for groups 1, 2 and 3 were 4.81 mm, 4.84 mm and 4.97 mm, respectively.
Using stepwise regression analysis, lens equatorial plane was the only statistically significant predictor for postoperative anterior chamber depth. Preoperative anterior chamber depth, lens thickness and lens vaulting were not statistically significant predictors for postoperative anterior chamber depth. – by Robert Linnehan
Disclosure: Yoo reports no relevant financial disclosures.
Perspective
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Uday Devgan, MD
Many decades ago, ophthalmologists primarily relied on preop refraction to estimate the IOL power for cataract surgery. This evolved into using the keratometry and axial length, first with regression (SRK I and SRK II) and then with theoretical formulae (Holladay 1, SRK/T and Hoffer Q). This proved reliable for most eyes, but it soon became clear that more input variables, such as anterior chamber depth, could help predict the effective lens position (ELP) of the IOL more accurately. This factor, determining the precise ELP, is the primary challenge for truly accurate IOL calculations.
We now use the keratometry and axial length as the two primary factors for IOL calculations, with other data such as anterior chamber depth, white-to-white, refraction, lens thickness and more to help hone the ELP determination. These newer formulae such as the Holladay 2, Haigis, Olsen and Barrett Universal II tend to be more accurate than their predecessors, and many surgeons have abandoned the older methods, which were based on refraction, regression and only two-input variables.
Lens calculation methods continue to evolve, and there will be more factors that play a role in honing IOL calculations, such as the lens equatorial plane as mentioned in this study by Dr. Yoo and colleagues. Based on this study, lens equatorial plane appears to be an important factor that can be incorporated into our calculations. And there may be more important variables in the future such as posterior corneal power and angle measurement.
One thing is certain: Methods of IOL power calculation will continue to evolve, and static formulae will eventually become outdated. This is why the future of IOL calculations will be using methods such as artificial intelligence, neural networks and big data. This new technology is embraced by the Hill-RBF and the Ladas Super Formula 2.0 Artificial Intelligence. These machine learning methods will be able to incorporate new factors such as lens equatorial plane to become more accurate. Already, we can achieve more than 90% of patients within 0.5 D of target, and that is a huge improvement compared with just a decade ago.
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