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D. A. Taylor; The Feasibility of Self Tonometry by Patients: Comparison of Self-Taken Diurnal IOP Values Between a Normal Control Subject and a Glaucomatous Patient. Invest. Ophthalmol. Vis. Sci. 2010;51(13):577.
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To investigate the feasibility and potential value of home-based self tonometry by demonstrating accuracy, repeatability, and operator independence.
Two Reichert AT555 auto aligning / auto measuring non-contact tonometers were used to measure IOP. Both instruments were calibrated (rubber eye fixture) and human eye verified to demonstrate accuracy and repeatability. A normal (control) subject and a glaucoma (OD) subject each recorded a minimum of 5 IOP measurements per eye, per day during the waking hours over a 7-day period while maintaining a normal daily home and work routine. Measurements were made in a seated position. Three (3) measurements per eye were taken at the time of each session. OD and OS measurements were made in alternating fashion until 3 measurements per eye had been acquired. The average of the three measurements for each eye was recorded as the IOP value in mmHg. Subjects were masked to the IOP values while making them. Activities prior to measurement were noted during the data recording process. The glaucoma subject instilled one drop of Xalatan OD each night before bed, with the exception of one day when the Xalatan was delayed until 7AM the following morning. A total of 56 IOP measurements were recorded by the normal control subject and 46 by the glaucoma subject over the 7-day period.
Mean IOP values for the normal subject were 16.5 OD, 16.0 OS and 20.4 OD, 20.5 OS for the glaucoma subject. OD/OSIOP correlation was R2=0.89 for the normal subject and R2=0.19 for the glaucoma subject. Average range of daily pressure variations was 9.6 OD, 9.0 OS for the normal subject and 3.6 OD, 4.3 OS for the glaucoma subject. Peak IOP values for the normal subject always occurred upon the first morning measurement whereas peak IOP values for the glaucoma subject, or values equal to the peak morning IOP, were recorded 3 days OD and 7 days OS. Noted activities during the 7-day period, such as smoking, exercise, and rest had immediate short-term impacts on IOP for the normal subject. Time of medication for the glaucoma subject had an impact on the daily IOP values. Medication taken in the AM, rather then PM, resulted in the lowest and most stable diurnal IOP.
Auto Non-contact tonometry requires minimal training and can provide unbiased, repeatable, and easy to perform self tonometry. IOP monitoring by self-tonometry may provide valuable information not available from sporadic measurement that will enable physicians to customize treatment regiments, similar to the way Diabetes is monitored and controlled.
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