Biomechanical Corneal Parameters in Eyes With Chronic Ocular Hypotony and in Non-Hypotonic Eyes. Self-Controlled Case Series Study.

Abstract

Introduction: There are no available data concerning corneal parameters in patients with chronic ocular hypotony. Our purpose is to provide evidence and clinical correlation on the biomechanical corneal changes in chronic hypotonic eyes.

Patients and methods: A single-center, transversal, self-controlled case series study was conducted involving patients with at least one chronic hypotonic eye (defined as an intraocular pressure ≤6.5 mmHg measured on three separate occasions for at least three months). The chronic hypotonic eye was the case and the contralateral eye the control (non-hypotonic eye). We collected data from baseline characteristic and intraocular pressure (mmHg). Biomechanical corneal parameters measured by Corvis ST: deformation amplitude ratio (mm), Ambrósio's relational thickness (μm), stiffness parameter at first applanation (mmHg/mm), Integrated radius (mm^-1), stress-strain index, pachymetry (μm), and in addition macular folds were recorded as well. A descriptive and exploratory analysis was performed.

Results: Between November 2021 and July 2023, a total of 16 consecutive patients (7 men, 9 women; age [median (range)]: 72 (62-84)), diagnosed with chronic ocular hypotony in one eye were included: 16 chronic hypotonic eyes and 16 non-hypotonic eyes. Hypotonic versus non-hypotonic eyes [median (range)]: intraocular pressure: 4 (2-6) mmHg, 16 (8-38) mmHg; deformation amplitude ratio: 5.6 (4.3-6.6) mm, 4.7 (3.9-5.5) mm, p-value= 0.002; Ambrósio's relational thickness: 482 (263-932) μm, 530 (210-818) μm, p-value: 0.845; stiffness parameter at first applanation: 61.5 (39-100) mmHg/mm, 113 (68-130) mmHg/mm, p-value: <0.001; Integrated radius: 10.9 mm^-1 (6.3-16.8), 7.9 mm^-1 (6.4-10.5), p-value: <0.001; stress-strain index: 0.7 (-0.2-4.9), 1.1 (-2.7-5.6), p-value: 0.034; pachymetry 509 (456-617) μm, 512 (436-775) μm, p-value: 0.637; and macular folds: 7/16, 0/16, p-value: <0.001.

Conclusions: Chronic hypotonic eyes (eyes with a low intraocular pressure) present biomechanical corneal changes with respect to non-hypotonic eyes, mainly in deformation amplitude ratio, stiffness parameter at first applanation, stress-strain index and Ambrósio's relational thickness parameters. These biomechanical corneal changes could reflect softer, more elastic and deformable scleras, which at its turn can bear higher risk of hypotony maculopathy.