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Shu-Hao Lu, I. T. Chong, Stanley Y. Y. Leung, David C. C. Lam; Characterization of Corneal Biomechanical Properties and Determination of Natural Intraocular Pressure Using CID-GAT. Trans. Vis. Sci. Tech. 2019;8(5):10. doi: 10.1167/tvst.8.5.10.
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© ARVO (1962-2015); The Authors (2016-present)
The intraocular pressure (IOP) measured using Goldmann Applanation Tonometry (GAT) is confounded by individual corneal properties. We investigated a modified method that removes the confoundment by incorporating corneal properties into the Imbert-Fick's law is investigated.
Porcine eyes were pressurized between 10 and 40 mm Hg using a manometer. The eyes were indented using a flat cylindrical indenter. A modified corneal indentation device (CID) procedure was used to obtain the corneal moduli Eqs. The calculated IOPNC from the Imbert-Fick's Law using the corneal moduli Eqs was compared to the natural IOPN, measured using pressure sensor inserted into the eye.
Test results showed that IOP-dependent corneal modulus Eqs is a primary confounding factor in IOP calculation. The average elastic modulus Eqs is 0.173 ± 0.018 MPa at 20 mm Hg, and increases with IOP at a linear rate of 0.0066 MPa per mm Hg (r = 0.997, P < 0.001). Incorporation of individual Eqs into IOPNC calculation showed that IOPNC are in good agreement with reference IOPN (slope = 0.999, r = 0.939, P < 0.001).
The IOP-dependent corneal modulus Eqs is a primary confounding factor in IOP calculation. A modified CID-GAT procedure to obtain natural cornea-independent IOPNC is developed and verified in this study. The CID-GAT IOP modification may be used in place of conventional GAT when the confounding effects in eyes with atypical cornea (e.g., laser-assisted in situ keratomileusis [LASIK] thinned) are significant.
Confoundment from corneal properties results in IOP measurement errors. The study showed that the CID-GAT method can significantly reduce the confounding corneal errors.
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