An experimental protocol of the model to quantify traction applied to the retina by vitreous cutters

The purpose of this study was to use a novel method to quantify the traction applied to the retina during vitrectomy.

Five 20-gauge electric cutters were used. Fresh porcine eyes were positioned in a specially developed holder and transfixed to the retinal layers with a microwire, and the other end was fixed to the load cell of a strain gauge. The cutter to be assessed was introduced into the eye by a micromanipulator at a 45 degrees angle adjacent to the retina. The traction force was evaluated when the cutter was at 3 and 5 mm from the retina. As control, the experiment was repeated in eyes filled with water, and the results were compared to those when the eyes had vitreous gel.

Results from the eyes with vitreous gel indicate that retinal traction increased with increasing aspiration vacuum (7.90 dyn for each 100 mm Hg increased; P < 0.05) and proximity to the retina (2.17 dyn; P < 0.05) and decreased with increasing cut rate (2.51 dyn for each 500 cuts per minute increased; P < 0.05). In all eyes filled with water, traction was not observed.

The present study establishes a new reproducible technique to quantify vitreoretinal traction during vitrectomy and demonstrates that the effects of aspiration, distance from the retina, and cut rate are crucial factors in the amount of retinal traction created by vitreous cutters.