November 2018

RESIDENTS

EyeWorld journal club
Review of “OCT analysis of phacoemulsification incisions: could tighter incisions delay recovery? A prospective randomized trial of 2.2 mm versus 2.85 mm incisions”


by Alexis Flowers, MD, Alexander de Castro-Abeger, MD, MBA, Thomas A. Mendel, MD, PhD, Joshua M. Barnett, MD, PhD, and Laura L. Wayman, MD, Department of Ophthalmology, Vanderbilt University Medical Center


Laura Wayman, MD, vice chair for education, Department of Ophthalmology, Vanderbilt University Medical Center


Vanderbilt University Medical Center residents, from left: Thomas Mendel, MD, PhD, Alexander de Castro-Abeger, MD, MBA, Joshua Barnett, MD, PhD, and Alexis Flowers, MD

 

Much effort has been directed toward achieving micro-incisional cataract surgery, but just how beneficial is this? The Vanderbilt residents review an interesting study comparing different sub-3.0 mm incisions in the November issue of JCRS.

—David F. Chang, MD,
EyeWorld journal club editor

Introduction

This prospective, double-masked, randomized study aimed to compare post-cataract clear corneal incision wound integrity and endothelial cell characteristics between two incisional sizes using anterior segment optical coherence tomography (AS-OCT) and specular microscopy analysis. The premise of this study was that while advances in cataract surgery have led to smaller self-sealing clear corneal incisions, some studies have suggested these smaller incisions may actually be associated with decreased wound integrity. The authors argued the importance of this study based on the current culture of patients’ high expectations of expeditious visual recovery post-cataract surgery. They thought that understanding the factors that lead to good quality incisions could reduce the risk of endophthalmitis. The study compared two incision sizes, 2.85 mm and 2.20 mm, and followed patients for 3 months after uncomplicated cataract surgery. This distinguished the study from others, which only followed patients for 1 month postoperatively. They evaluated incision architecture and endothelial cell damage using AS-OCT and specular microscopy and found that smaller incisions had higher rates of Descemet’s membrane detachments (DMDs), endothelial polymorphism, and endothelial cell density (ECD) loss, which delayed healing and led to slower visual recovery. There was no difference in DMDs, visual acuity, or incision thickness at 3 months.

Methods

This was a prospective study with the goal of enrolling 100 patients to power the study. The exclusion criteria were appropriate to avoid confounders such as previous corneal problems, astigmatism greater than 2 diopters, previous eye trauma or injury and visual acuity targets that were not emmetropic. Patients were then randomly assigned to have either a 2.20 mm or a 2.85 mm main corneal incision. A single surgeon allowed for consistency in wound construction, but leads the reader to question whether the results can be generalized to other surgeons. The surgical procedure was relatively consistent; however, two different phacoemulsification tips were used to accommodate the two incision sizes. Did this difference impact the findings? The positive features of this study were: standardization of testing with the AS-OCT and specular microscopy, the author’s explanation of the methods, and the statistical analysis.

Results

The authors reported in the results section that they enrolled 100 eyes from 100 patients and that 98% were included in the study outcomes (one was lost to follow-up and one with poor quality AS-OCT imaging, both lost from the 2.85 mm incision size group, reducing the study’s sensitivity to detect differences in the compared groups). They demonstrated similar baseline characteristics (age, race, sex, uncorrected distance visual acuity, various corneal characteristics, etc.) without significant differences. The population in each group is described as predominantly New Zealand Europeans and 10% or less of Mãori, Asians and Pacific Islanders, which is potentially limiting to the broader application of the study results. The authors described an increase in phacoemulsification time with higher scored cataracts by the Lens Opacities Classification System III as would be expected from prior studies,1 and an increase in incision thickness up to 1 month.
The primary outcomes were related to corneal incision healing: DMD, epithelial wound gaping, endothelial polymegathism, and corneal thickness up to 3 months after surgery. At 1 day and 1 month following surgery there was a significant difference (P=0.01 and 0.04, respectively) in DMD with higher detachments in the 2.20 mm incision group. This difference had resolved by the 1-month follow-up, and there was no DMD at the 3-month follow-up. The authors reported that the patients with DMD have lower preoperative ECD (P=0.01) and decreased UCVA at 1-day and 1-week follow-up as well as increased endothelial wound gaping and increased incision thickness at all follow-up times. Interestingly, the 2.20 mm incision group started with an average ECD that was about 130 cells/mm2 lower than the 2.85 mm incision group, but this was not statistically significant (P=0.10). Epithelial wound gaping was higher in the 2.85 mm incision group at day 1 (P=0.06), and endothelial wound gaping was higher in the 2.20 mm incision group (P=0.06). This had resolved in either case by 1 month. Posterior incision recession (PIR) was found to increase from 1 week to 3 months equally in each group. This PIR is consistent with what has been previously demonstrated by other investigators looking at corneal wound healing and scar revision.2 Endothelial polymegathism (while not statistically different at baseline; 29.5% [2.20 mm] and 28.3% [2.85 mm] [P=0.07]) was significantly increased in the 2.20 mm group at 1 week and 1 month (P=0.02 and P<0.01). However, the differences resolved by 3 months. There was no difference found in pleomorphism between groups, and both groups demonstrated an expected decrease in ECD from baseline at 3 months without an intergroup difference. The authors demonstrate that the incision width measured postoperatively by AS-OCT is smaller in the 2.20 mm incision group at all follow-up times as would be expected.
Finally, the authors compared the incision characteristics by measuring the angle between the incision and the tangent of the corneal epithelial surface at the incision entry point and the incision size at follow-up. They found the main incision angle to be smaller than the paracentesis incision angle (25.03 degrees vs. 36.62 degrees) regardless of initial incision size, suggesting that this smaller angle aides in preventing incision leakage. They report that a single main incision (with a larger angle, 35 degrees) and all paracentesis incisions leaked initially and required stromal hydration potentially contributing to prolonged recovery. Comparing incision sizes at follow-up, the authors reported that the incision length was not different at any time point regardless of initial incision size. The larger 2.85 mm incisions had correspondingly larger incision widths at all time points relative to the 2.20 mm incisions. Both groups had a reduction in incision length and width from day 1 to month 1 without any change beyond this point.

Discussion

In this study, the authors compared uniplanar clear corneal incisions of two sizes (either 2.20 mm or 2.85 mm), and they reported that the smaller 2.20 mm incision was associated with increased rate of traumatic DMDs, linking that result to slower healing times. They go on to hypothesize that the “relative tightness” of the lens cartridge within the smaller wounds results in more wound stretch. Impressively, they went on to consider the planar circumference of the ellipsoid lens cartridge and determine that the fully dilated 2.20 mm incision possesses a circumference 0.81 mm less than that of the cartridge, resulting in wound stretch.
The authors presented considerations regarding the impact of the different phacoemulsification tips utilized in the different size incisions, defending the selection of each tip being certified for incisions significantly smaller than the study incisions. Rather than measure “tightness” of the incisions around each phacoemulsification tip, the authors suggest using incision size as surrogate marker. Given the different corneal thickness and stiffness characteristics of each operated cornea, it may have been preferable to measure tightness with an appropriately sized instrument. This would have been particularly helpful given that the authors go on to suggest that mechanical stretching of the wound is a component of the poor wound healing observed with the smaller incisions.
Noting that the smaller 2.20 mm incision resulted in increased endothelial dysfunction with polymegathism, the authors speculated that perhaps the varying fluidics of the different phacoemulsification tips were the culprit. While they cite that “fluid flow through a cylindrical phacoemulsification tip is exponentially proportional to the inverse diameter of the tip,” they did not measure or demonstrate either an increased rate of flow or increased turbulence. Actual experimental demonstration of increased flow, turbulence, or untoward effect on endothelium would have been preferable.
The authors next considered the merits and complications of wound hydration in uniplanar incisions. The authors reference that some of the main incisions and some of the paracenteses required wound hydration to seal. Without notation about how many wounds were hydrated to seal, it is unclear to what degree this confounding factor influenced the results.
In spite of these few, small missed opportunities for more precise measurement and data collection with regard to “wound tightness” evaluation, the authors present a compelling paper for consideration against the general trend to reduce incision size in ocular surgery. By demonstrating an increased rate of DMD and slower wound healing with the smaller 2.20 mm incision, they provide a rationale for practicing surgeons to continue utilizing the larger 2.85 mm clear corneal incisions, particularly in patients who are prone to corneal endothelial damage.

References

1. Davison JA, Chylack LT. Clinical application of the lens opacities classification system III in the performance of phacoemulsification. J Cataract Refract Surg. 2003;29:138–45.
2. Wang L, et al. Healing changes in clear corneal cataract incisions evaluated using Fourier-domain optical coherence tomography. J Cataract Refract Surg. 2012;38:660–5.

Contact information

Wayman: laura.l.wayman@vanderbilt.edu

Review of “OCT analysis of phacoemulsification incisions: could tighter incisions delay recovery? A prospective randomized trial of 2.2 mm versus 2.85 mm incisions” Review of “OCT analysis of phacoemulsification incisions: could tighter incisions delay recovery? A
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