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T. Realini, G. Hobbs, R. N. Weinreb; Reproducibility of Central Corneal Thickness Measurements in Healthy and Glaucomatous Eyes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4911.
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To determine the distribution of differences in central corneal thickness (CCT) values measured repeatedly over time in healthy and glaucomatous individuals.
88 eyes of 44 primary open-angle glaucoma (POAG) patients and 76 eyes of 37 healthy subjects underwent ultrasound pachymetry at 8AM on day 0, day 7, day 30, day 180 and day 365. Five measurements in each eye were taken on each day; the average of the five measurements represented the CCT value for each day. The highest and lowest values from among the five daily averages (ie, the highest day and the lowest day) were identified for each eye; the measurement difference was the difference of the highest minus the lowest CCT value for each eye. The distributions of CCT measurement differences in healthy eyes and POAG eyes were determined and compared to each other using the chi-square test.
Healthy subjects and POAG patients were demographically similar (mean age 67.0 vs 63.9 yr, 100% vs 89% Caucasian, and 68% vs 64% female, respectively). Mean CCT was 563.7 ± 31.9 microns in healthy eyes and 553.6 ± 43.7 microns in POAG eyes. Mean CCT measurement difference (maximum minus minimum values for each eye) was 26.2 ± 15.1 microns in healthy eyes and 23.9 ± 15.0 microns in POAG eyes. The distribution of differences is given in the table. The distributions of CCT measurement differences were similar in healthy vs POAG eyes (chi-square = 3.35, p = 0.50).
CCT measurements vary significantly over time in both healthy and POAG eyes; 26% of healthy eyes and 20% of POAG eyes had CCT measurements that differed by more than 30 microns between visits. This may represent variation in measurement technique, true CCT variation over time, or both. A single CCT measurement in the lifetime of a POAG patient may not suffice in characterizing CCT.
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