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D. Epstein, P. Vinciguerra, F. Camesasca, G. Luca; Dynamic Contour Tonometry to Accurately Measure IOP in Extremely Thin Post–excimer Corneas . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2747.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate dynamic contour tonometry (DCT), a novel method for measuring IOP not influenced by corneal thickness or curvature, in extremely thin post–excimer corneas. Previous experience has shown that Goldmann applanation tonometry (GAT) provides inaccurately low IOP readings in corneas thinned by the excimer procedure. Methods:Thirty–seven eyes which had previously undergone up to 4 photorefractive keratectomies (PRK) were included in the study. Mean (±SD) preoperative spherical equivalent was –8.18D±2.04D. Mean preoperative IOP (GAT) was 14.79 mm Hg±2.03 mm Hg (range, 10.0–18.0 mm Hg), mean corneal thickness 546.63mµ±43.59mµ (range, 496–674mµ), and mean preoperative keratometry 43.40D±0.81D (range, 41.45–44.70D). Since DCT had not been invented at the time of the initial PRKs, a control group of 30 normal (virgin) eyes, in which GAT was compared with DCT, was also tested. Corneal thickness was also documented in this group. Results: The mean postoperative IOP (GAT) was 7.71 mm Hg±2.21 mm Hg (range, 4.0–12.0 mm Hg). By contrast, mean postoperative IOP as measured with DCT was 15.88 mm Hg±3.0 mm Hg (range, 10.80–22.0 mm Hg), significantly different from the GAT readings but not significantly different from preoperative GAT. Mean postoperative corneal thickness was 365.71mµ±94.11mµ (range, 258–535mµ), and mean thinning ranged from 157.33mµ to 244.83mµ. There was no significant correlation between the magnitude of thinning and the GAT underestimation of IOP. Mean postoperative keratometry was 36.66D±1.48D (range, 32.77–39.11D). The control eyes, with a mean pachymetry of 538.94mµ±19.24mµ, displayed similar means and practically identical ranges for both GAT and DCT. Conclusions: Dynamic contour tonometry provides a more accurate measurement of IOP in post–excimer eyes than gold standard GAT. Since GAT is based on the assumption of normal corneal thickness and keratometry, it underestimates IOP in the thinner–than–normal cornea of the excimer treated eye. The finding that DCT maintains its accuracy even in the presence of extremely thin corneas supports previous evidence of its reliability.
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