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T. Paul, N. M. Radcliffe, M. Shimmyo; Reclassification of Normal- and High-Tension Glaucoma Eyes Using Corneal Compensated Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2849.
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The accuracy of Goldmann applanation tonometry (GAT) in measuring intraocular pressure (IOP) is affected by material properties of the cornea. We measured IOP by GAT and corneal compensated IOP (IOPcc) using Reichert's Ocular Response Analyzer (ORA) to evaluate whether use of IOPcc would affect the classification of eyes into normal- and high-tension categories.
Cross-sectional observational review. IOP measurements of 1875 consecutive patients in a general ophthalmology practice were reviewed. Corneal hysteresis (CH), corneal resistance factor (CRF) and central corneal thickness (CCT) of randomly selected one eye of 357 normal, 155 high tension glaucoma (HTG) and 102 normal tension glaucoma (NTG) were compared. Eyes were classified as normal or glaucomatous based on the absence or presence of glaucomatous optic neuropathy (GON). The highest GAT recorded in a patient in an untreated state was used to divide patients into HTG (>21 mmHg) and NTG (< or = to 21mmHg) categories.
The mean IOPcc and GAT were similar in normal eyes and HTG eyes. In NTG eyes, the mean IOPcc of 19.8 mmHg was considerably higher than the mean GAT of 14.4 mmHg. In addition, NTG eyes had significantly thinner mean CCT of 513 µm, a lower CH of 5.96 mmHg, and a lower CRF of 6.31 mmHg (p<0.001) when compared to normal eyes which had a mean CCT of 541 µm, CH of 10.6 mmHg, and CRF of 10.15 mmHg. Many eyes (72%) considered to have NTG by traditional GAT threshold of 21mmHg were reclassified as HTG by IOPcc threshold of 18mmHg.
In NTG eyes, corneal compensated IOP measurements reveal a higher IOP than traditional GAT measurements.
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