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J. W. Branch, C. E. Callahan, J. Scott, F. Fantes; Sequence of Pachymetry and Tonometry in the Ophthalmic Examination. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1257. doi: https://doi.org/.
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To determine if the sequence of intraocular pressure measurement and corneal thickness measurement is important in the ophthalmic examination.
This was a randomized, prospective study examining forty-three patients and normal volunteers from Bascom Palmer and University of South Florida, with no history of prior intraocular surgery or laser therapy, ages 18-75, who presented to the glaucoma clinic for routine evaluation. Patients that suffered from eye disease that affected the accuracy of tonometry or pachymetry readings were excluded. After informed consent was obtained, subjects were randomized into two groups, either initial pachymetry, or initial tonometry measurement of the right eye. One eye was measured in the sequence pachymetry-tonometry-pachymetry. The fellow eye was measured in the sequence tonometry-pachymetry-tonometry. A single examiner, utilizing the Goldman Applanation Tonometer and the Pachette© Ultrasound Pachymeter, sequentially performed the measurements. Less than one minute elapsed between measurements. Patient demographic data, diagnosis, and ocular medications were recorded.
In the tonometry first eye, the initial IOP remained stable within ≤ 1.5 mm Hg in 34/43 eyes. 8/43 eyes experienced a decrease in IOP by ≥ 2 mm Hg following pachymetry testing, and 1/43 eyes exhibited an increase in IOP of ≥ 2 mm Hg. In the pachymetry first eye, the corneal thickness following tonometry remained stable within 5µ for 38/43 participants and within 10µ for all participants. IOP measured after pachymetry was a mean of 0.907mm Hg +/- 1.13 less than when measured before (P=0.000002, 95% CI 0.569-1.245). Pachymetry when measured after applanation was a mean of 0.1micrometer +/-3.2 less than when measured before (P=0.424, 95% CI -0.856-1.058)
Measurement of corneal thickness prior to evaluation of intraocular pressure may influence the accuracy of the intraocular pressure reading. Pachymetry measurements may be obtained immediately following tonometry in the routine ophthalmological exam without significantly affecting the accuracy of the corneal thickness reading.
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