On Repeated Tonometry

Abstract

The fact that repeated tonometry is associated with an apparent fall in intraocular pressure was first noted by Stocker 1958 and Goldmann 1958. Since then it has been strongly confirmed (Moses 1961, Bechrakis 1966 and there is full agreement on the following points:1. When the measurements are repeated every minute there is a fall of 3-4 mm Hg in 5 minutes and about 5 mm Hg in 12 minutes. According to Bechrakis the fall is exponential. On the contralateral eye there is a sympathetic pressure fall.2. The decline in intraocular pressure is observed both on normal subjects and patients with glaucoma.3. The effect is found both on seated patients and on supine patients, both with applanation tonometry and with Schiotz tonometers. On the other hand, there are differences in opinion as to the effect of accommodation (Armaly, Bechrakis) and anaesthetics.The mechanism of this phenomenon is still obscure, and there are a few elementary questions to he answered before it can be tackled.1. Is the effect due to an interference from the measuring instrument or is the mere sitting at the instrument enough to elicit it? In the former case, how soon is the presure restored?2. Is the weight of the instrument resting on the cornea of any importance to the magnitude of the effect? Is it possible to measure the intraocular pressure at all without provoking the effect?

Comparison of two handheld applanation tonometers and the association of central corneal thickness, age, and intraocular pressure in normal and diseased canine eyes

“…Moreover, many investigators have reported problems with IOP values decreasing during successive measurements using applanation tonometers . Repeated applanation IOP measurements in humans may iatrogenically alter the measured IOP value, with both linear and exponential changes reported . Whitacre et al .…”

Central and peripheral intraocular pressure measured by a rebound tonometer

“…IOP decreases when it is measured consecutively with various tonometers, as in the case of IOP measurements by GAT, a phenomenon that was first pointed out during the development of the tonometer 2,20. Significant IOP-lowering effects as a result of consecutive measurements are not seen with Icare, or are less than those associated with consecutive measurements using a GAT 21.…”

Two-position measurement of intraocular pressure by PT100 noncontact tonometry in comparison with Goldmann tonometry

“…Goldmann applanation tonometer measurements were performed after use of the noncontact tonometer to eliminate the reported possible effect of ocular massage by the Goldmann applanation tonometer 20. In the second measurement session, except for randomization, the order of use of the instruments and the eye assessed was the same as in session 1.…”