More stable surgery may help better predict effective IOL position

A lens fragmentation device can help to maintain zonular integrity, which can improve refractive outcomes, explain Kenneth J. Hoffer, MD, FACS, and Gerald J. Roper, MD.

Exacting IOL power calculations are required to provide optimal refractive results to patients following cataract surgery. One of the most common sources of error in these calculations remains the effective lens position (ELP). It is difficult to determine this exact healed postoperative axial position from preoperative biometric data.

The ELP may be reasonably estimated by the vector physics and mathematics of the latest IOL calculation formulas, though validating this specific parameter for error is limited by challenges in determining the postoperative axial IOL final lens position (FLP). Going forward, swept-source ocular coherence tomography images on newer biometers may be able to help assess the accuracy of the ELP calculation parameter in the various formulas.

The FLP will be compared with the ELP estimates of the IOL axial position, presuming that surgical technique will not significantly influence zonular support. We realize, however, that the surgery may well have an effect. In eyes that have had previous corneal surgery, it is also challenging to determine the exact power of the cornea.¹

Formulas such as the Barrett Universal II, Haigis, Hoffer H-5, Holladay 2, Olsen, and others address more variables than in the past.²

ELP still surgical challengeFor as many advances as surgeons have at their disposal, both diagnostically and in the operating room, accurately achieving the desired postoperative refraction remains a challenge. Further, surgeons’ willingness to fully embrace premium lens solutions for their patients depends upon their comfort level with their results.

When patients are paying additionally for a truly refractive result from their implant surgery, surgeons are under pressure to nail outcomes precisely. Disparities between the predicted ELP to the resultant FLP has been shown to contribute more than 35% of mean absolute error.³

It is the most common cause of residual refractive error, followed by postoperative refraction variability, preoperative axial length measurement, and pupillary size variation (Figure 1). A factor influencing the FLP, compared with the ELP, may be zonular integrity.

Any part of the cataract procedure that strains the zonules or works against their integrity may contribute to less stability of the fibrosed lens capsule axial position and thus to less predictability of the refractive result. Current investigations suggest that when zonular integrity is better maintained for 360°, accuracy in achieving the refractive target seems to increase. It would stand to reason that sagging due to zonular breaks or rupture would leave the lens in a different axial position and bearing from the anatomical predictions of ELP used to determine calculations.

Preoperative measurements that predict where the lens will sit after surgery presume intact zonules. Simply, if zonules break, ELP may become less accurate; that’s our theory. By keeping the zonules intact, ELP prediction may be enhanced.

Clinical experience
A recent comprehensive data set overview of 374 cataract surgery patients at one of the author’s practices (GJR) revealed a mean absolute error was 0.23 D. After considering the relationship between zonular integrity and ELP, the decision was made to incorporate the lens fragmentation device (miLOOP, Carl Zeiss Meditec/ianTECH).

The self-expanding, nitinol filament technology ensnares the nucleus allowing for full-thickness fragmentation. It works independent of phaco energy, using instead centripetal (out-in) disassembly to minimize capsular stress and cut the nucleus in half. It was hoped that routine use of the device would avoid disrupting zonules and improve excellent refractive outcomes.

The device’s sweeping motion along the inside of the lens capsule is a gentle maneuver, according to the surgeon (GJR). There was no significant decrease in zonular integrity observed throughout the surgical cases, and the learning curve was relatively short.

A data review of the clinic’s first 50 miLOOP cases for 8-week refractive outcomes, using otherwise usual protocol and identical criteria as previous cases. The mean absolute error dropped to 0.15 D.

More confident recommendations
With the lens fragmentation device, under the proper technique, there is little front to back or translational displacement of the lens when it is placed in the capsular bag (Figure 2). By incorporating the lens fragmentation device, surgeons may enhance their cataract surgery process and move closer to delivering excellent refractive outcomes to patients (Figures 3 to 5).

More predictable results may allow surgeons to more fully participate in recommending and implanting premium IOL technology. CONCLUSION Maintaining zonular integrity may help conquer one of the issues that holds surgeons back from achieving more accurate refractive outcomes on a consistent basis.

The lens fragmentation device is a tool that may enhance zonular integrity and perhaps the refractive outcomes. These factors may help to ensure the lens is placed in its intended position.

Disclosures:

Kenneth J. Hoffer, MD
E: khoffermd@aol.com
Dr. Hoffer is a clinical professor of ophthalmology at Jules Stein Eye Institute, University of California, Los Angeles. He did not indicate any proprietary interest in the subject matter.

Gerald R. Roper, MD
E: ropergj@gmail.com
Dr. Roper is in private practice at Advanced Eye Care, Batesville, IN. Dr. Roper is a consultant to IanTECH.

References:

1. Savini G, Hoffer KJ. Intraocular lens power calculation in eyes with previous corneal refractive surgery. Eye Vis (Lond). 2018;5:18. doi: 10.1186/s40662-018-0110-5. eCollection 2018.

2. Hoffer KJ, Savini G. Clinical results of the Hoffer H-5 formula in 2707 eyes: First 5th-generation formula based on gender and race. Intl Ophthalmol Clin. 2017;57:213-219. doi: 10.1097/ IIO.0000000000000183.

3. Norrby S. Sources of error in intraocular lens power calculation. J Cataract Refract Surg. 2008;34:368- 376.