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S. Kling, P. Perez-Merino, S. Ortiz, D. Pascual, S. Marcos; Corneal Biomechanical Response to Intraocular Pressure Changes From Scheimpflug and Anterior Segment OCT. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4628.
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© ARVO (1962-2015); The Authors (2016-present)
To study corneal deformation upon varying intraocular pressure (IOP) on a whole eye porcine model from quantitative anterior segment imaging techniques.
Enucleated intact porcine eyes were imaged while IOP was increased by 40 mmHg and then decreased (at 5 mmHg steps). Inflation was performed by infusing saline solution into the posterior chamber. The pumping system, IOP monitor, moist chamber humidity and temperature sensing, and image capture were fully automatized. Three-dimensional images were captured using a previously validated Scheimpflug imaging system (25 meridional scans, 15.8 mm lateral range) and a custom-built anterior segment spectral Optical Coherence Tomography (100 A-scans x 1000 B-scans, 19 mm lateral range). Custom algorithms were developed to segment the anterior and posterior corneal surfaces and for correction of fan and optical distortion correction in OCT 3D images. The central area (6-mm diameter) of the anterior and posterior corneal surfaces was fitted by conics. Anterior and posterior corneal shape, central corneal thickness and apical shift were estimated from both Scheimplug and OCT, while OCT also allowed to measure axial shift of the limbus. A total of 17 eyes were measured 4-hours after enucleation (in 16 eyes the measurements were repeated after 24 h). Typically one eye was measured using OCT and the contralateral eye with Scheimpflug. A control experiment to understand the role of corneal hydration on the biomechanical response involved dextran treatment and/or epithelium debridement.
(1) OCT and Scheimpflug showed changes of the same order of magnitude, but no correlation between both eyes of the pig was observed. (2) Scheimpflug maximum corneal thickness change was -17.8um(0h)/-24.4um(24h), anterior radius change was 52.4um(0h)/76.2um(24h) and posterior radius change 89.6um(0h)/230um(24h) at an IOP increase of 40mmHg. (3) After IOP variation curvature and thickness showed significant hysteresis. (4) Corneal dehydration caused by dextran is x1.2 smaller in eyes with epithelium than without. The application of dextran produced curvature changes of ~2 times higher than without. (5) IOP changes produced apical as well as limbal displacements
Scheimpflug imaging and OCT provide geometrical corneal changes with IOP which can be used to analyze corneal biomechanics and be introduced in finite element models. Corneal deformation is susceptible to hydration.
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