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C. Bergin, A. Kotecha, A. Spratt, C. Bunce, D. F. Garway-Heath; The Relationship Between Diurnal Changes in Corneal Thickness, Intraocular Pressure and Corneal Hysteresis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1250.
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Sixty-two eyes of 62 untreated glaucoma suspects & normal controls had IOP measurements performed with the GAT (mmHg) and DCT (mmHg) over an 8 hour period at 2-hourly intervals from 9 am. Corneal characteristics measured were central corneal thickness (CCT; µm) using a non-contact optical low-coherence reflectometry pachymeter and corneal hysteresis (CH; mmHg) measured with the ORA. In addition, 2 further corneal biomechanical properties, the corneal constant factor (CCF; mmHg) and corneal resistance factor (CRF; mmHg), were calculated from the CH value.Changes in IOP (Δ IOP) and corneal characteristics (Δ CC) between each 2-hour time point were calculated, and correlations assessed using the Pearson correlation coefficient.
Table 1 shows the mean change in IOP (Δ IOP) and CC (Δ CC) over the day (9am to 5pm) and at each 2 hour interval. The difference between Δ GAT and Δ DCT IOP measurements were significant at the 9am to 5pm interval (mean difference 0.80 mmHg, t-test p=0.01). CCT reduced over the day, whilst corneal biomechanical properties reduced over the first 4 hours and stabilised after 3pm. There was no correlation between Δ IOP and Δ CC between each 2 hour time interval. However, at the 9am to 5pm interval, Δ GAT correlated with Δ CCF (r=0.27, p<0.05) and with Δ CRF (r=0.36, p<0.01), and Δ DCT correlated to Δ CCF (r=0.28, p<0.05).Table 1: Change in IOP and CC over the day (n = 62; SD = standard deviation, Δ = change in each parameter).
Corneal characteristics show small changes over normal office hours. Larger magnitude changes in IOP measurement are correlated with changes in CCF and CRF.
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