Evaluating multi-planar clear corneal incision architecture with microscope-integrated OCT (MIOCT)

Abstract

Purpose : Multi-planar clear corneal incisions (CCI) are the standard in cataract surgery for better wound closure and hence decreased risk of endophthalmitis. However, in previous limited experience examining cataract surgery incisions with OCT, we have not observed distinct incision multi-planarity. We sought to test the hypothesis that the manual multi-planar CCI may not actually be multi-planar.

Methods : Under controlled wetlab conditions, 4 ophthalmic surgeons with prior cataract experience (2 attendings, 2 residents) were re-familiarized with the multi-planar CCI and instructed to make 3 CCIs with a standard 2.4 mm keratome in porcine eyes. Each eye’s anterior chamber was filled with viscodispersive prior to the 3 incisions. A research swept source MIOCT (1050 nm, 400 kHz) captured volumes at the CCIs (15 x 15 x 7.2 mm consisting of 750 B-scans x 750 A-scans x 950 depth pixels). For analysis, the anterior surface of each CCI was semi-automatically segmented. Each incision’s center B-scan was refraction corrected and used to calculate the following metrics: incision length, length:width ratio, and internal angles. The internal angles were the angles between the incision’s entry, center, and exit vectors calculated from the first 5%, mid 30%, and last 5% of incision length respectively (Fig. 1E). A Wilcoxon Signed-Rank test was performed to compare both sets of angles to the theoretical 90° of an ideal multi-planar incision and to 135° for a less acute multi-planar incision.

Results : Table 1 shows the metrics for each surgeon’s CCIs. The null-hypotheses (entry and exit angles are part of distribution around 90°) were rejected in the t-tests (p =4.9x10^-4 and 4.9x10^-4). The result was the same with the t-test against 135° (p =4.9x10^-4 and 4.9x10^-4). All incisions had mean length:width ratios >=0.82.

Conclusions : CCIs created with a standard keratome do not appear to have multi-planarity in model porcine corneas. Despite this, length:width ratios show nearly square incisions, and the increased surface area from attempted multi-planar CCIs likely contributes to clinical incision closure.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Table 1: Incision path lengths, length:width ratios, and internal angles with mean/SD for each surgeon (2 attendings, 2 residents)

 

Figure 1: Representative B-scans cropped to the CCI location (attendings: A,B – residents: C,D). The red line is the segmentation of the anterior face of the CCI. E defines the angle metrics.