Biomechanical analysis of Corvis tonometry parameters in patients with hypotony after glaucoma filtering surgery

Abstract

Aims/Purpose: Postoperative hypotony is a common complication of glaucoma filtering surgery, particularly with adjunctive use of antimetabolites, such as mitomycin C and 5‐fluorouracil. Precautions may be taken intraoperatively and postoperatively to decrease the likelihood of hypotony. Sometimes, despite these measures, the low‐pressure syndrome still can occur, the management of which can be difficult. The cornea has a complex biomechanical structure that determines its response under stress conditions and there are so many studies related with glaucoma and corneal biomechanical properties. However, in the best of our knowledge, there are no reports concerning the corneal parameters in patients with hypotony. This study aimed to investigate the possible correlation of hypotony risk after a filtering surgery with different corneal parameters obtained by Corvis.Methods: A retrospective case control study of 30 eyes with chronic hypotony (IOP ≤6 mmHg for more than a month) after glaucoma filtering surgery at the Hospital Universitari Germans Trias i Pujol. In all patients, the IOP (represented in mmHg) and following parameters were obtained using the Corvis device: deformation amplitude ratio (DA), Ambrósio's relational thickness (ARTh), stiffness parameter at first applanation (SPA1), Integrated radius (IR), Stress strain index (SSI) and pachymetry (represented in μm).Results: The results will be represented as the value in eyes with hypotony after glaucoma filtering surgery (cases) vs the healthy eye (control). IOP 4.4 ± 1.8 vs 18.1 ± 7.7. Pachymetry 527 ± 53.4 vs 549.1 ± 94. SPA1 65.2 ± 19.1 vs 111 ± 17.1 in controls (p < 0.05). ARTh 495 ± 170 vs 523 ± 222. IR 10.9 ± 2.67 vs 8.4 ± 1.36 (p < 0.05). DA 5.6 ± 0.7 vs 5 ± 0.5 (p < 0.05). SSI 1.3 ± 1.4 vs 1.6 ± 1.4.Conclusions: SP‐A1 value decreased while the IOP decreased, suggesting that the lower corneal stiffness could increase the percentage of hypotony due to the different ocular biomechanical properties in these eyes, so therefore, it could be considered a risk marker for hypotonia in patients who are going to undergo glaucoma filtering surgery.