Purpose:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Keywords: clinical laboratory testing • eye movements • eyelid