Tono-Pen, a new tonometer.

UNLABELLED: The Tono-Pen is a miniaturized Mackay-Marg tonometer with electronic signal analysis and digital pressure display. In study 1, we compared the Tono-Pen with Goldmann tonometry in 108 healthy human subjects (216 eyes). In 33 of these subjects, the IOP was changed in a range between 0 and 50 mmHg by a scleral suction-cup system. In study 2, the Tono-Pen was compared with a Statham membrane manometer in 6 humans (12 eyes), 3-6h after death. The IOP was changed in a range between 0 and 60 mmHg by an infusion system. -
RESULTS: Related to the Goldmann tonometer, the Tono-Pen gave a small overestimation of IOP below 16 mmHg (maximum deviation 1.5 mmHg at 0 mmHg Goldmann reading). Above 16 mmHg, however, the Tono-Pen increasingly underestimated the IOP determined by Goldmann tonometry (maximum deviation 8 mmHg at 50 mmHg Goldmann reading). Related to the manometer, the Tono-Pen gave a small overestimation of IOP below 17 mmHg and small underestimation above 17 mmHg (maximum deviation 2.5 mmHg at manometer readings of 0 and 60 mmHg, respectively). -
CONCLUSIONS: Throughout the entire clinically relevant IOP range, an acceptable relationship between Tono-Pen and manometer readings was found in human cadaver eyes, whereas the relationship between Tono-Pen and Goldmann tonometric readings in the clinical study was found to be acceptable only in the low and physiological IOP range. The considerable deviation from the Goldmann readings in the high IOP range requires further modifications of the Tono-Pen.