Rapid learning curve assessment in an ex vivo training system for microincisional glaucoma surgery

Abstract

Purpose : Microincisional glaucoma surgeons operate in a highly confined space, making it difficult to learn by observation or assistance alone. An ex vivo model would allow for better refinement of technique, quantification of progress and computation of a learning curve.

Methods :
Seven resident trainees without angle surgery experience performed nine ab interno trabeculectomies in pig eyes after preparing with training slides and videos. They placed the eyes on a tiltable mannequin head, visualized the trabecular meshwork gonioscopically through an ophthalmic microscope and removed it by trabectome-mediated plasma ablation(Figure 1). An expert surgeon observed, guided, and rated the procedure using an Operating Room Score (ORS). The extent of accessed outflow beds was estimated with canalograms using 0.5-micron fluorescent microspheres. Data was fit using mixed effect models.

Results :
ORS was fit by an asymptotic nonlinear mixed effects model with a fixed upper asymptote, an estimated lower asymptote, and an estimated logarithmic rate constant, and including random effects for the lower asymptote and for the rate constant. A half-maximum was achieved after 2.5 eyes. Surgical time decreased by 1.4 minutes per eye in a linear fashion. The ablation arc followed a sigmoidal function with a half-maximum inflection point after 5.3 eyes and the mean arc improved from 73 to 135°. Despite these changes, canalograms revealed that the improvement in arc angle did not correlate well with improvement in outflow(Figure 2).

Conclusions :
This inexpensive pig eye model provides a safe and effective training model for ab interno trabeculectomy and allows for quantification of outcomes. Trainees without prior angle surgery experience proceeded quickly on the learning curve. Actual outflow improvements progressed at a slower rate, a reminder to remain humbly committed to training.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1. Setup for microinvasive glaucoma surgery.

 

Figure 2. A)The Operating Room Score (ORS). B) Surgical time and eye number. C)The improvement of ablation arc length . D)Fluorescent canalograms along the individual learning curve of trainees #1 through #7