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K.R. Lovelace, T. Realini; Central Corneal Thickness and the Amplitude of Daily IOP Fluctuation in Normal Subjects . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2215.
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Purpose: Diurnal intraocular pressure (IOP) fluctuation is a known independent risk factor for disease progression in glaucomatous eyes. Variation in central corneal thickness (CCT) affects IOP measurement by Goldmann tonometry, and the magnitude of this effect may vary nonlinearly with both CCT and with measured Goldmann IOP. This pilot study was carried out to determine if the amplitude of daytime Goldmann IOP fluctuation varies with CCT in normal subjects. Methods: 30 normal subjects (normal corneas and no glaucoma) underwent Goldmann tonometry in the right eye at 8AM, 10AM, noon, 2PM and 4PM on the same day. At least two measurements per time point were collected and averaged. After the 4PM IOP measurement, CCT was assessed by ultrasound pachymetry (mean of five measurements per eye). The amplitude of daytime IOP fluctuation (IOP maximum minus IOP minimum) was calculated for each eye. Results: The average daytime IOP fluctuation among 30 normal right eyes was 3.8 mmHg (range, 0.5 to 8.0 mmHg). The average CCT was 564 microns (range, 481 to 660 microns). Linear regression analysis demonstrated no correlation between CCT and the amplitude of daytime IOP fluctuation (Pearson correlation coefficient r = 0.02, r-squared = 0.0004, p=0.91). The slope of the line obtained by plotting CCT versus IOP amplitude was 0.4 microns per mmHg, essentially flat over the observed range of CCT. Conclusions: At least in the range of normal IOP among normal subjects, there is no demonstrable correlation between the amplitude of daytime IOP fluctuation and central corneal thickness.
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