Astigmatism management at the time of cataract surgery is something that, in my opinion, all surgeons should be comfortable addressing. Whether you treat it with a blade, laser, or intraocular lens (IOL), management of astigmatism is critical to ensure optimal postoperative vision.
It's estimated that 37.5% of cataract patients have astigmatism >1 D. (Market Scope, 2013, Comprehensive Report on Global IOL Market). Depending on the axis and magnitude of astigmatism, most will recommend corneal-based treatments for lower astigmatism and toric IOLs for higher astigmatism. Each surgeon has his or her own threshold for what they consider lower and higher amounts of astigmatism. I am a believer in posterior corneal astigmatism (PCA) and its effect on refractive outcomes.
Factoring PCA into your astigmatism calculations is now very easy, as most commercially available calculators (Barrett Toric Calculator, Johnson & Johnson, Alcon, others) allow for PCA compensation. Whether or not you compensate for PCA will affect your threshold for corneal- vs lens-based approaches to astigmatism management.
Ocular surface optimization is one of the more important steps in astigmatism management. Assuring for regular astigmatism and that values are in agreement across various measurement modalities (eg, biometer, topographer, tomographer, auto-refractor, others) is essential.
Although toric IOLs are very safe and effective in managing astigmatism, their penetration in the US market remains limited. There are many factors beyond the scope of this commentary to explain why the penetration is not higher, but one common fear is postoperative rotation of the toric IOL off the intended target axis.
Certainly, there are many factors that may affect the stability of toric IOL alignment, including the length of eye, removal of lens epithelial cells/capsule polishing, axis of astigmatism, make and model of IOL, and removal of the ophthalmic viscosurgical device (OVD) from behind IOL, among others. However, for most of these factors, there are contradictory studies showing both their importance or lack of importance.
In this installment of Viewpoints, I'll review an intriguing study by Sasaki and colleagues of the effect of anterior capsule overlap on the rotational stability of a toric IOL. This was a prospective study of 110 eyes after implantation of AcrySof toric IOLs. In brief, the study found the only variable associated with IOL rotation at 6 months postoperatively was complete or partial anterior capsule overlap. Other variables studied (with multiple regression analysis) included age, anterior chamber depth, axial length, type of astigmatism (WTR, ATR, oblique), area of rhexis, and individual surgeon). The group with complete overlap of the rhexis had a mean absolute rotation that was approximately half of the group with partial rhexis overlap (roughly 2 degrees vs 4 degrees, P = .0004).
In 2021, we have three ways to perform a capsulotomy (manual, femtosecond, precision pulse). The study by Sasaki and colleagues highlights the importance of achieving complete overlap of the rhexis over the IOL to improve rotational stability. Although the absolute difference in rotation was small, it was highly statistically significant. Consistent with other studies, the majority of rotation was seen in the first hour after surgery (in both groups).
This highlights the importance of being meticulous with respect to your technique and making sure patients are counseled to avoid activity and eye rubbing after surgery. The study did not explore IOL tilt, IOL decentration, or effective lens position (ELP) changes, all of which can also affect refractive results. Nonetheless, given the results of this study, I will continue to strive for a centered capsulorhexis with complete overlap in all of my cataract patients!
J Cataract Refract Surg. Published May 1, 2021. Abstract
Sumit (Sam) Garg, MD, is the vice chair of clinical ophthalmology and an associate professor in the Department of Ophthalmology at the Gavin Herbert Eye Institute, University of California, in Irvine. He specializes in corneal and cataract surgery as well as laser refractive surgery.
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Cite this: Astigmatism Management in Cataract Surgery Depends on Anterior Capsule Overlap - Medscape - Jun 28, 2021.