Intraoperative Optical Coherence Tomography Imaging For Assessment Of Anterior Chamber Gas Fill During Endothelial Keratoplasty

During endothelial keratoplasty, surgeons titrate the amount of gas in the anterior chamber to their desired fill. The assessment of this fill is difficult by en-face visualization alone. The purpose of this study is to evaluate how this fill correlates with intraocular pressure (IOP) and iris angle identified by optical coherence tomography (OCT).

University-based research laboratory.

Cadaveric human eyes were mounted on a stand and examined using a microscope with intraoperative anterior segment OCT. Study data was obtained for three different configurations: baseline, with an air fill that just spanned limbus to limbus (“full-fill”), and an air fill that maximally filled the entire anterior chamber (“overfill”). At  each configuration IOP was measured by Tonopen and anterior segment OCT images were obtained. Iris angle (between root of the iris and peripheral cornea) was obtained by analyzing intraoperative OCT images with ImageJ software.

In evaluation of 11 cadaveric human eyes, no differences in IOP or iris angles were identified between the baseline and full-fill configurations (p = 0.113 and p = 0.152, respectively). When compared to the overfill configuration, differences in IOP and iris angles were identified for the baseline configuration (p = 0.001 and p = 0.001,  respectively) as well as the full-fill configuration (p = 0.001 and p = 0.039, respectively).

This data suggests that visualization alone of a full gas fill may not be indicative of IOP elevation, should that be the surgeon's goal. There is a difference in IOP and iris angles between full-fill and overfill configurations. With intraoperative OCT, significant widening of the iridocorneal angle is observed, which can serve as a useful surrogate to assess the extent of gas fill.