Tonometer utilization, accuracy, and calibration under field conditions
I. F. Wessels and Y. Oh
Department of Ophthalmology, Loma Linda, University, CA 92354.
A field survey conducted in 94 ophthalmologists' offices in our immediate
area assessed the accuracy of tonometers in daily use. One hundred
eighty-five instruments were examined: 127 were slit lamp mounted, 48 were
hand held, and 10 were noncontact devices. Nineteen percent of applanation
tonometers were outside the manufacturers' specifications (1 mm Hg of the
calibration) and 4.5% were more than 2 mm Hg in error. The error was
constant across the scale. Hand-held applanators were less accurate than
those on slit lamps (P less than .02); the latter demonstrated an
association between accuracy and age (P less than .05) and heavier use (P
less than .01). Annual recalibration was performed in 86% of instruments.
Those practitioners who themselves performed the calibration had the most
accurate instruments. Less than 15% knew how to perform the calibration
check.
