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To evaluate the influence of central corneal thickness (CCT) and its 24-hour fluctuation on 24-hour intraocular pressure (IOP) fluctuation in primary open-angle glaucoma.Forty consecutive patients underwent 24-hour evaluation (8 PM, midnight, 4 AM, 8 AM, noon, and 4 PM) of supine and sitting IOP, measured with handheld Perkins and Goldmann tonometer respectively, and of CCT measured using ultrasonic pachymeter. Thirty patients were treated with timolol 0.5% twice daily and latanoprost 0.005% once daily; 10 patients were untreated. Measurements were taken in both eyes, but only one eye per patient was used for analytical purposes. Three IOP curves were drawn: sitting position, supine position, and habitual body position (diurnal sitting measurements and nocturnal supine measurements). Fluctuation was calculated as the SD over the 24-hour curve. Differences in the 2 groups were inspected by means of t test; the correlations between IOP fluctuation and mean CCT, respectively, and its fluctuation were evaluated by means of regression analysis.Untreated patients had higher IOP than the treated group (habitual body position: 22.1±5.1 mm Hg vs. 16.0±3.0 mm Hg, P=0.004), but no differences were found for IOP fluctuations (habitual body position: 2.5±1.2 mm Hg vs. 2.3±0.8 mm Hg, P=0.32), mean CCT (542±38 μm vs. 534±39 μm, P=0.44), and CCT fluctuation (8.7±5.6 μm vs. 6.5±3.0 μm, P=0.09). The correlation between IOP fluctuation and mean CCT and its fluctuation was not statistically significant at supine, sitting and habitual body positions (P≥0.07; R2≤0.20).Twenty-four–hour IOP fluctuation was independent from CCT parameters in both treated and untreated glaucoma patients, regardless of body position at which IOP was measured.