Introduction and clinical evaluation of servo-controlled applanation resonance tonometry

In recent years, Applanation Resonance Tonometry (ART) has been suggested for intraocular pressure (IOP) measurements. The manual version of ART (ART(manual) ) has been further developed, and to improve usability, an automatic servo-controlled prototype (ART(servo) ) has been proposed. The aim of this study was to assess the limits of agreement (LoA) of ART(manual) and ART(servo) as compared with the reference method, Goldmann Applanation Tonometry (GAT).

This was a prospective single-centre study on 152 eyes from 77 subjects. It was designed according to International Standard Organization's (ISO) requirements for tonometers (ISO 2001). Intraocular pressure was measured six times/method in a standardized order. The ART technique has two available analysis procedures: a dynamic one that measures IOP during the indentation phase and a static one that causes a Goldmann-like measurement during two seconds of full applanation. The 95% LoA was defined as ±1.96 × standard deviation of difference against GAT.

Mean IOP for GAT was 19.1 mmHg (range: 10-37 mmHg). The 95% LoA of ART(manual) was ±4.5 mmHg for both dynamic and static analyses. The 95% LoA of ART(servo) was ±5.7 mmHg for dynamic and ±4.9 mmHg for static analyses.

This study confirms that the ART methodology is feasible. The further developed ART(manual) fulfilled the ISO standard with both the dynamic and the static analysis techniques. ART(servo) with static analysis was close to fulfilling the standard but failed to do so in the highest IOP range. ART(servo) has the potential to greatly improve usability if further development is completed.