Tonometry in adults and children: A manometric evaluation of pneumatonometry, applanation, and TonoPen in vitro and in vivo

Objective: The purpose of the study was to determine the accuracy of applanation tonometry, pneumatonometry, and TonePen tonometry in adults and children and the effect of age on tonemeter error. Design: The design was divided into four parts: part 1 was prospective and cross-sectional, and parts 2 through 4 were prospective, cross-sectional, and masked. Participants: This study contained 72 patients representing 74 data points. Intervention: Tonometry with simultaneous manometry was performed. Main Outcome Measures: Intraocular pressure (IOP) and the tonometric estimate of IOP were obtained. Results: The normal pediatric IOP follows the line Ta = 0.71 age(years) + 10 up to age 10. Applanation tonometry under anesthesia differs from pneumatonometry by an average of -8.6 mmHg and is age related by the equation Ta = Tph + 2.6 log(age) - 10.3. The TonoPen was the most accurate instrument for enucleated eyes, and the pneumatonometer was the most accurate in anesthetized living eyes. Conclusions: Applanation tonometry markedly underestimated IOP in young eyes. TonoPen tonometry performed well with enucleated eyes but was not adequately accurate for clinical use. The pneumatonometer performed the best clinically and the best overall.