Central Corneal Thickness, Tonometry, and Ocular Dimensions in Glaucoma and Ocular Hypertension

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Abstract
To assess possible correlations between central corneal thickness, tonometry, and ocular dimensions. One hundred seventeen eyes of 117 patients who were not taking any intraocular pressure–lowering medications were studied prospectively. Forty-one patients had ocular hypertension; 13 patients had primary open-angle glaucoma; and 10 patients had normal-pressure glaucoma. Twenty-three healthy eyes were included. Thirty glaucoma suspects (10 patients monitored for possible normal-pressure glaucoma and 20 patients with intermittent ocular hypertension) were included for correlation analysis. Tonometry was performed with Goldmann applanation and pneumotonometry, and central corneal thickness, anterior chamber depth, lens thickness, and axial length were measured ultrasonically. Central corneal thickness was lowest in eyes with normal-pressure glaucoma (538 ± 51 μm), highest in eyes with ocular hypertension (570 ± 32 μm), and intermediate and similar in eyes with primary open-angle glaucoma and healthy eyes (547 ± 34 μm and 554 ± 32 μm, respectively). These differences were significant (P = 0.028). Goldmann applanation tonometry and central corneal thickness were weakly correlated (r = 0.12, P = 0.205), with a 0.2-mm Hg change per 10-μm variation in central corneal thickness. Pneumotonometry measurements were more strongly correlated with central corneal thickness (r = 0.21, P < 0.05). Lens thickness was strongly correlated with age (r = 0.57, P < 0.001). Anterior chamber depth was negatively correlated with lens thickness and age (r = −0.29, P < 0.005 and r = −0.25, P < 0.01). Axial length was correlated with anterior chamber depth and age (r = 0.5, P <.001 and r = −0.19, P < 0.05). Eyes diagnosed as having ocular hypertension have thicker corneas and eyes labeled as having normal-pressure glaucoma have thinner corneas, when compared with healthy eyes or eyes with primary open-angle glaucoma. The effect of central corneal thickness on Goldmann applanation tonometry accuracy appears to be small and usually not clinically relevant. When corneal thickness is markedly different from normal, the clinician may need to factor this into diagnosis and management.