Patients With Intravitreal Gas Bubbles at Risk of High Intraocular Pressure Without Exceeding Elevation of Surgery: Theoretical Analysis

Abstract

The purpose of this study was to show the mechanism responsible for high peak IOP in patients with intravitreal gas bubbles resulting from a descent to low elevation and a return ascent, without exceeding the surgical elevation. A computational model reconstructed four clinical cases, using published elevations, ascent rates, and initial bubble sizes. In each case, patients first underwent surgery (790 m), then went home (790 m, 790 m, 325 m, 240 m). When returning for follow-up visits, patients descended to a low elevation (20 m, 0 m, 25 m, -310 m), then ascended to surgical elevation (790 m). The computational model output bubble size, aqueous humor volume, and IOP during the patients' travels. A parametric study was conducted to investigate the role of each modeling parameter. All four simulated cases showed increased peak IOP (34-50 mm Hg). Intraocular pressure returned to a normal value (15 mm Hg) after prolonged exposure to the surgical elevation. Over the course of the entire path, the gas bubble volume changed approximately 5%, decreasing in size during descent and then increasing during ascent. In our simulations the change of bubble size outpaced the change of aqueous humor volume resulting in a 2-fold risk to patients. First, the bubble size reduction at the low elevation may increase the risk of ocular hypotony and postsurgical retinal detachment. Second, the combined increasing bubble size and accumulated aqueous humor puts patients at risk of high peak IOP after ascent even without exceeding the surgical elevation. The risks are primarily dependent on rates of elevation change and duration spent at the different elevations.