Intraocular Pressure Measurement with Pneumatonometry and a Tonometer Tip Cover

Purpose: To investigate the precision and accuracy of IOP measurements using a pneumatonometer and a tonometer tip cover (Tono-Pen^® tip cover) acting as a membrane between a cadaver eye model and pneumatonometer probe. Methods: A total of 480 paired IOP measurements, with and without a Tono-Pen cover, were collected across 4 pressure levels of 7, 10, 20 and 30 mmHg. IOP measurements were obtained by three different pneumatonometer units paired with three different masked operators (three configurations). Four eyes were sampled for each eye pressure level. The sequence of eye pressure, configuration, and measurements with vs. without the Tono-Pen cover was randomized. Results: With the Tono-Pen cover in place, there was a negative bias with a mean IOP difference of − 1.18 mmHg for all 480 paired samples compared with the measurements absent the cover. Compared with the test pressure settings (i.e., 7, 10, 20, 30 mmHg), the overall mean bias was + 0.35 mmHg with the Tono-Pen cover present. With the Tono-Pen cover present, the overall repeatability %CV (percent coefficient of variation) was 3.4% and the reproducibility %CV was 3.8% compared with a repeatability %CV of 3.2% and reproducibility %CV of 5.7% without the Tono-Pen cover. Conclusion: Measurement of IOP via pneumatonometry with a Tono-Pen cover in place, also known as the excursion test method, yields precise, accurate and reproducible results. This developed method of pressure measurement is an acceptable and reliable form of IOP measurement.