The Effect of Scleral Buckle Surgery on Tonographic Outflow Facility, Positional Intraocular Pressure, and Ocular Biomechanics

Purpose: To investigate the in vivo effect of scleral buckle surgery on ocular biomechanics and aqueous humor dynamics. Design: Prospective observational cross-sectional study. Participants: Nine patients with unilateral 360 degree encircling scleral buckles without vitrectomy for rhegmatogenous retinal detachments, between 3 and 39 months postoperative. Methods: All measurements were performed in both eyes of all participants. Intraocular pressure (IOP) was measured in the seated and supine positions using pneumatonometry. Outflow facility was measured using 2-minute weighted pneumatonography. Ocular rigidity coefficient was determined from the Friedenwald equations based on the difference in IOP with and without a weighted tonometer tip. The percentage change in IOP upon transitioning from seated to supine was calculated. Measurements for buckled and nonbuckled eyes were compared using paired Student t test of means. Main Outcome Measures: Sitting and supine IOP and percentage difference between the 2 positions; outflow facility; ocular rigidity coefficient. Results: Seated IOP was similar between buckled and nonbuckled eyes (16.1 ± 2.5 vs. 16.7 ± 2.7 mmHg; P = 0.5) whereas supine IOP was lower in buckled eyes compared with nonbuckled eyes (18.7 ± 2.6 vs. 21.3 ± 2.5 mmHg; P = 0.008). The percentage increase in IOP upon change in body position from seated to supine was greater in nonbuckled eyes (17.4 ± 9.4% vs. 27.6 ± 9.5%; P = 0.005). Ocular rigidity coefficient was lower in buckled (9.9 × 10^-3 ± 1.4 × 10^-3 μL^-1) vs. nonbuckled eyes (14.4 × 10^-3 ± 3.1 × 10^-3 μL^-1; P = 0.006). Outflow facility was not significantly different in buckled and nonbuckled eyes. Conclusions: Scleral buckling decreases ocular rigidity but does not affect outflow facility. This change in ocular biomechanics likely results in the attenuated IOP change from seated to supine position. Decreased ocular rigidity may also reduce IOP fluctuations and potentially reduce the risk for glaucoma progression. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.