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CCT not sole factor influencing IOP measurements, study indicates
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Measurements of IOP made using the Ocular Response Analyzer with corneal compensation are significantly influenced by corneal hysteresis, according to a study by researchers in Germany.
However, unlike Goldmann applanation tonometry, central corneal thickness (CCT) showed no effect on IOP, the study authors noted.
Annette Hager, MD, and colleagues investigated whether several biomechanical properties of the cornea affected IOP measurements obtained by three methods. The study included 156 normal eyes of 80 patients with neither corneal pathology nor glaucoma. All eyes underwent IOP measurements using Goldmann applanation tonometry, noncontact tonometry and the Ocular Response Analyzer (ORA) from Reichert, according to the study.
The researchers found that the measured IOP averaged 14.8 mm Hg using Goldmann tonometry, 16.4 mm Hg using noncontact tonometry and 16.2 mm Hg using the ORA with corneal compensation. Also, when using ORA, IOP averaged 10.6 mm Hg when considering corneal hysteresis and 10.9 mm Hg when considering corneal resistance factor, according to the study.
Central corneal thickness averaged 557 µm, the authors noted.
"In our group of normal eyes, [corneal compensated IOP] ... in contrast to [Goldmann tonometry] and [noncontact tonometry], does not depend on central corneal thickness," they said. "Corneal hysteresis and corneal resistance factor provide further information about biomechanical properties of the cornea beyond central corneal thickness."
The study is published in the June issue of Der Ophthalmologe.