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F. Nazemi, Y. Buys, G. Trope, C. Birt; The Effect of Repeated Pressure Measurements During Diurnal Tension Testing on Central Corneal Thickness. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1256.
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Corneal thickness has an influence on intraocular pressure readings. We assessed the effect of multiple applanation tonometry measurements and repeated topical anaesthetic/fluorescein drops on readings of central corneal thickness (CCT).
After obtaining informed consent we measured CCT on 57 patients before and after a diurnal tension curve determination (8-12 applanation tonometry measurements, starting at 8AM and ending between 9-10PM), and at the same times on 11 volunteers who did not undergo applanation tonometry. The subjects mean age was 63.5 years (range, 27-90). There were 27 females and 29 males, using on average 1.5 glaucoma medications. The racial composition included 40 Caucasians, 5 white non-Caucasian, 8 Asians and 4 of African descent. In the control group there were 9 Caucasians and 2 white non-Caucasian, with a mean age of 59.5.
We used the right eye measurements in all cases for our calculations. The mean CCT in study subjects before the first applanation at 8AM was 546.1 µm (SD 38.4) and after last applanation at 9-10PM was 545.3 µm (SD 38.9). In control group the mean CCT at 8AM was 537.8 µm (SD 45.9) and at 9-10PM was 534.7 µm (SD 44.9). Paired t-tests did not show any significant difference between CCT at the beginning and at the end of the day in either group.
It has been shown in other studies that topical anesthetic drops and applanation tonometry cause small changes in CCT. Studies also show 24- hour variation in CCT and IOP. Our results show that repeated applanation tonometry has no significant effect on central corneal thickness.
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