Intra-eye pressure range and pulse profiles in normals with the pulsair non-contact tonometer

Abstract

SUMMARYThe difference in intraocular pressure (lOP) between the highest and lowest measurements on an eye with non contact tonometry (the range) has been reported to be less than 4 mmHg in most normals. The range of lOP to be expected with the Keeler Pulsair in normals over the age of 50 years was determined by analysing the results of lOP recordings on 741 normal individuals. Between 56% and 62% of eyes recorded a range >4 mmHg and between 4% and 8% a range >10 mmHg when four pulses per eye were used. Population pulse profile analy sis indicated that this was not due to an erroneously high first pulse in a set of four, and that lOP asymmetry pre viously reported when screening females is due to a generalised tendency for lOPs in right eyes to measure higher than those recorded in the left. The occurrence of a range ofIOP recordings up to 10 mmHg in an eye is rela tively common with the Pulsair and individuals under going glaucoma screening with this instrument should not be referred purely on the basis of a large lOP range.Non-contact tonometry (NeT) samples the ocular pulse by causing a momentary applanation event on the cornea with a ramped jet of air. In order to estimate the mean intraocular pressure (lOP) in an eye, a number of NeT pulses are used. The Keeler Pulsair NeT was introduced in 1988.1 We have reported previously on the effect of altering the number of pulses used to estimate the lOP in a population at risk of glaucoma,2 and the asymmetry to be expected in normal individuals when using the Keeler Pul sair NeT. 3 In the latter study we demonstrated that, when screening for glaucoma, normal individuals record an lOP which is on average 0.63 mmHg higher in the right eye than the left eye when the right eye is tested first. The effect is marked in females, reaching a level of statistical significance of p<O.OOO 1; in males asymmetry just fails to reach statistical significance (p<0.07).

A New Tonometer—The Corvis ST Tonometer: Clinical Comparison with Noncontact and Goldmann Applanation Tonometers

“…As a result, applanation time becomes a significant factor affecting the difference in IOP readings. 16 With the CST, the separation between the two applanations is approximately 15 ms. It is plausible, therefore, that the difference in IOP measurements between the CST and GAT may be greater in patients with a longer applanation time.…”

Measurement of Intraocular Pressure with a Modern Noncontact Tonometer

“…In cases of ranges exceeding 8 mm Hg, a repetition of the set of measurements has been recommended [9, 10, 11, 17, 26]. In the present study, the median range of readings with the Pulsair NCT was 3.0 mm Hg.…”

“…Interocular pressure differences within 3–5 mm Hg were accepted as normal [21]. However, the results are controversial [19, 21, 22, 23, 26, 27, 28]. While in some studies, IOP in the right eye was reported to be higher than in the left [23, 26, 28], others found no interocular asymmetry [19, 22].…”

“…The range of 3 consecutive IOP measurements in one eye was not statistically different between right and left eyes. In previous studies, the difference between female and male subjects with regard to the range of IOP measurements was not found to be significant [19, 26]. …”

“…The range of interocular asymmetry for noncontact tonometry in a normal population seems to be higher than that for Goldmann applanation tonometry [28]. When the average value of 3 measurements per eye was used to estimate the IOP in 874 subjects, the 95% confidence intervals for the interocular-IOP asymmetry in normals was found to be 0.65±5.88 mm Hg [26]. In the present study, the mean (± SD) interocular IOP difference was 1.9±1.6 mm Hg, and the median value was 1.7 mm Hg (lower quartile/upper quartile 0.7/2.7).…”