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Abstract #19751 Published in IGR 9-4
The influence of corneal hysteresis and corneal resistance factor on the measurement of intraocular pressure
Hager A; Schroeder B; Sadeghi M; Grossherr M; Wiegand WOphthalmologe 2007; 104: 484-489
The influence of central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) has been discussed extensively in recent years. The problem, however, has not been solved so far. In addition to CCT there are probably further biomechanical properties that play a role in IOP measurement. We wanted to find out whether these properties are related to Goldmann applanation tonometry (GAT), noncontact tonometry (NCT), or CCT. Biomechanical properties of the cornea such as corneal hysteresis (CH) and corneal resistance factor (CRF) can be measured with the Ocular Response Analyzer (ORA, Reichert Ophthalmic Instruments, Depew, NY, USA). Furthermore, a corneal compensated IOP (IOPcc) is given. We examined 156 normal eyes of 80 patients who did not show corneal pathology nor glaucoma. In each eye GAT, NCT, and ORA data as well as CCT were measured. Data were statistically analyzed with respect to agreement and the influence of CH and CRF on IOP measurement. In our patients the following average values were calculated: GAT 14.8 ± 3.0 mmHg, NCT 16.4 ± 3.9 mmHg, IOPcc 16.2 ± 4.1 mmHg, CH 10.6 ± 2.3 mmHg, CRF 10.9 ± 2.4 mmHg, and CCT 557 ± 36 μm. IOPcc was not related to CCT in normal eyes and the only IOP value related to CH (p < 0.01). CRF, however, was related to GAT and NCT values (p < 0.01). In our group of normal eyes IOPcc, i.e., the value that is adjusted by measurement of viscoelastic properties of the cornea, in contrast to GAT and NCT does not depend on central corneal thickness. Corneal hysteresis and corneal resistance factor provide further information about biomechanical properties of the cornea beyond central corneal thickness.
Dr. A. Hager, Augenabteilung, Asklepios Klinik Nord - Heidberg, Tangstedter Landstrasse 400, 22415 Hamburg, Germany. anhager@gmx.de
Classification:
6.1.3 Factors affecting IOP (Part of: 6 Clinical examination methods > 6.1 Intraocular pressure measurement; factors affecting IOP)
2.2 Cornea (Part of: 2 Anatomical structures in glaucoma)