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Gordon A. Thomas, Robert D. Fechtner; Dynamic Alignment for Transpalpebral Tonometry. Invest. Ophthalmol. Vis. Sci. 2011;52(14):684.
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We are fabricating and testing a tonometer that would allow a patient to measure intraocular pressure (IOP) and aid in the diagnosis and monitoring of glaucoma. For reasons of patient safety and comfort we use a transpalpebral configuration and have improved the alignment protocol.
Our improvement is dynamic alignment, which increases reproducibility of the IOP measurement. We have carried out over 100 measurements in our laboratory using a gentle robotic palpation that operates 1st in a constant position mode with a 0.5mm depression of the palpebrum with a force of 1g, and 2nd in a moving mode toward the eye, palpating the palpebrum and cornea over a distance and force range up to that of a Goldmann aplanation tonometer. We record electronic signals with a National Instruments A/D converter feeding a computer and indicating 1st the central corneal position and 2nd the IOP.
In the 1st mode we measure a curve of the force as a function of the angle of the eye orientation using the physiological feature of the cornea as a partial sphere with its radial center offset from that of the eye. We fit this curve with a lobe of a sin function and the corneal center at the maximum. With the eye aligned at the corneal center the second mode produces a linear curve with a correlation factor of typically 0.98 or better and p=0.005 or better for distances up to 1mm and forces up to 2 g. The slope, combined with a separate measurement of the palpebrum, determines the IOP and is reproducible to typically 0.2mmHg.
The dynamically aligned tonometer output shows a reproducibility that is improved over previous measurements without dynamic alignment and may provide a practical approach for personal tonometry.
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