[Clinical evaluation of a new tonometer on the basis of international standard ISO 8612]

There is a continuous process of development of new tonometer types following different measurement principles on the tonometer market. A new tonometer working on the dynamic contour measurement principle is currently available for ophthalmologists. This device has special properties, since it determines the intraocular pressure as well as the ocular pulse amplitude. So far, clinical comparison measurements exist between the new tonometer Pascal and the applanation tonometer by Goldmann albeit without any reference to a standard. Besides, these measurements cover only a small pressure range between 7 mmHg and 23 mmHg which is not sufficient for medical diagnosis.

This new tonometer was investigated by clinical comparison measurements according to the currently valid international standard for human eye tonometers (ISO 8612). The tested tonometer determines the intraocular pressure without fluorescein. In an ophthalmogical hospital in Berlin the clinical comparison measurements were carried out by ophthalmologists on 127 patients according to the methods and criteria of the above-mentioned standard. A calibrated AT 870 from the Haag-Streit company served as reference tonometer.

The different cornea surface geometries of individual eyes, the variation of tear liquid volume, and also the different elastic properties of the human eye due to a large variation in rigidity led to measurements of intraocular pressure by this tonometer with an excessively high number of outliers p (i) (i = 1, ..., 3) per group (p (1) = 16.28 %, p (2) = 8.85 %, p (3) = 15.69 %, 5.0 % outliers per group only are permitted for the differences method), which do not correspond to the requirements of the international standard for tonometers ISO 8612. This is also shown by application of total method of least squares of regression line (slope a = 0.964, interception b = 2.868 mmHg, standard deviation s (y) = 2.628 mmHg).

The test of conformity of results of clinical comparison measurements to the international standard for tonometers ISO 8612 is the target of this work. The measurement results of the investigated tonometer are analysed and discussed according to this standard. Statements about the medical application of this medical measurement device for ophthalmologists are presented. According to the presented investigations the requirements of this international standard are not fulfilled by the tonometer Pascal.