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Karin R Pillunat, Eberhard Spoerl, Naim Terai, Lutz E Pillunat; Change in corneal biomechanical parameters following trabeculectomy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2025.
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© ARVO (1962-2015); The Authors (2016-present)
Aim of the study was to evaluate corneal biomechanical changes after trabeculectomy and the impact on intraocular pressure (IOP) measurements.
30 consecutive patients with open-angle glaucoma scheduled for trabeculectomy (TE) with mitomycin C were enrolled in this prospective case-control study. Corneal biomechanical parameters were assessed with the Ocular Response Analyzer (ORA, Reichert Inc. Depew, New York,USA) immediately prior and at least 6 months after uncomplicated TE. Main outcome measures were changes in corneal hysteresis (CH) and corneal resistance factor (CRF). IOP was measured with Goldmann applanation tonometry (GAT) and with the ORA: IOPg (Goldmann correlated) and IOPcc (corneal compensated). SPSS and linear mixed models with IOP as covariate were used to compare the parameters before and after TE.
After correcting for IOP dependency CH (before TE 8.00±1.35 mmHg; after TE 7.12±1.36 mmHg, P=0.011) and CRF (before TE 8.59±1.64 mmHg; after TE 7.49±1.67 mmHg, P=0.015) were statistically significantly lower after TE. IOP dropped statistically significantly: GAT from 21.7±11.3 mmHg to 9.6±2.6 mmHg (P=0.001), IOPg from 23.7±14.9 mmHg to 9.4±4.6 mmHg (P=0.001) and IOPcc from 26.9±15.2 mmHg to 13.2±4.8 mmHg (P=0.001). Preoperatively IOPcc was 20% higher than GAT (P=0.001) and 15% higher than IOPg (P=0.001). Postoperatively IOPcc was 37% higher than GAT (P=0.001) and 40% higher than IOPg (P=0.001).
Despite a marked IOP reduction IOP-adjusted CH and CRF do not increase after TE but rather decrease. The elastic capacity and viscous damping after TE are affected in such a way that the stress and strain relationship changes to a level where stress can be compensated by strain again. It is very much likely that we underestimate GAT measurements especially after surgery.
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