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H.A. Quigley, A.T. Broman, K. Bandeen–Roche, N.G. Congdon; Influence of Corneal and Other Ocular Characteristics on Measurement of Intraocular Pressure by Three Tonometers . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4868.
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Purpose: To estimate the influence of ocular characteristics on instrument measurements of intraocular pressure (IOP). Methods:A clinic–based sample of 230 patients with glaucoma, ocular hypertension, or suspected glaucoma underwent IOP measurement with Goldmann applanation, Tonopen, and Reichert Non–Contact tonometer (NCT). Measurement order was randomized by eye and instrument. Ocular characteristics measured included axial length (IOL Master), corneal curvature, corneal thickness (ultrasonic pachymetry), and corneal hysteresis (by NCT), a putative measure of corneal bioelasticity. We examined the relationship of average IOP (over the 3 tonometers) with these ocular characteristics adjusted for age, gender, race, corneal edema, and glaucoma therapy (any medication, past trabeculectomy or glaucoma surgery); generalized estimating equations were used to account for correlation between subjects and instruments. Categorical variables were used to account for tonometer differences from the overall average IOP. Results: In this cohort, the average age was 65 years (range 20–95), with 172 (75%) having present or past glaucoma treatment. In a multivariate model, high average IOP was associated with thicker cornea and steeper corneal curvature, but not with axial length. Hysteresis was related to average IOP in a quadradic manner, with the lowest and highest hysteresis values being associated with higher IOP values than mid–range hysteresis. With respect to difference in tonometer measurements, Goldmann was least affected by corneal thickness, the NCT was least affected by corneal curvature, and the Tonopen was least affected by hysteresis. Conclusions: Properties of the cornea other than its thickness appear to play a role in tonometric estimation of IOP. Each tonometer had strengths in being less affected by particular ocular characteristics. Corneal bioelastic response merits further study.
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