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Debbie S Kuo, Yvonne Ou, Bennie H Jeng, Robert B Bhisitkul, Jay M Stewart, Jacque L Duncan, Ying Han; Correlation Between Serial Scleral and Corneal Intraocular Pressure Measurements by Pneumatonometry. Invest. Ophthalmol. Vis. Sci. 2014;55(13):144.
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Intraocular pressure (IOP) is typically measured over the cornea, which is problematic for patients with significant corneal pathology or keratoprostheses. Scleral pneumoatonometry has been proposed as an alternative for monitoring IOP in these patients, however the relationship between change in scleral IOP and change in corneal IOP is unknown. In this study, we measured serial scleral and corneal pneumatonometry in patients receiving intravitreal injections, which transiently increase IOP, to evaluate the relationship between these two measurements over a broad range of IOPs.
Adults from the UCSF Retina clinic receiving intravitreal anti-VEGF injections were recruited for this prospective study. Measurements of central corneal thickness by pachymetry and serial corneal and temporal scleral IOP by pneumatonometry (baseline, immediately and 10, 20 and 30 minutes post-injection) were collected.
Thirty-three eyes (33 patients, ages 34-94 years, 5 with glaucoma, 17 pseudophakic) were analyzed. Scleral and corneal IOP pneumatonometry showed strong correlation (ICC: 0.89, 95% CI: 0.86-0.92), but scleral IOP averaged 9.0 mmHg higher than corneal IOP by Bland-Altman plot (95% limits of agreement: -1.5 to 19.5 mmHg). The slope from linear regression on individual patient data (mean R2= 0.93, SD: 0.08), which is the change in scleral IOP compared to the change in corneal IOP for each patient, averaged 1.01 (SD: 0.34). There was no significant difference in slope between patients with and without glaucoma (p=0.33, t-test) or patients who were phakic or pseudophakic (p=0.33, t-test), and slope was not correlated with age (r: -.0.26, p=0.15) or central corneal thickness (r: -0.28, p=0.11). Linear regression of data from all patients resulted in the following equation: scleral IOP = 0.99 corneal IOP + 9.23 (R2=0.81, p<0.0001).
Scleral pneumatonometry is strongly correlated to corneal pneumatonometry, and demonstrated a nearly 1:1 linear relationship over a range of physiologically relevant IOPs. The relationship between scleral IOP and corneal IOP was not impacted by age, central corneal thickness, glaucoma, or lens status in our patient population. In patients with significant corneal pathology, scleral pneumatonometry should be considered as a useful tool for diagnosing and managing glaucoma.
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