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

Abstract

BackgroundThe purpose of this study was to evaluate the precision of intraocular pressure measurements obtained by PT100 noncontact tonometry in a handheld and slit lamp-mounted position in comparison with that of Goldmann applanation tonometry in healthy young adults.MethodsSixty eyes from 60 subjects (30 men and 30 women) aged 22 ± 1 (range 20–24) years participated in this study. Triplicate intraocular pressure measurement of a randomly selected eye was obtained by a noncontact tonometer in a handheld and slit lamp-mounted position in a randomized order, with the Goldmann applanation tonometer always performed last. A second measurement session was carried out after one week to assess repeatability.ResultsThe mean ± standard deviation of intraocular pressure readings in the first and second session, respectively, with the three techniques were: handheld position, 14.52 ± 3.28 mmHg and 15.26 ± 2.11 mmHg; slit lamp-mounted position, 14.01 ± 2.80 mmHg and 15.16 ± 2.34 mmHg; and Goldmann applanation tonometer, 14.86 ± 3.26 mmHg and 15.16 ± 2.42 mmHg. There were no significant differences (P > 0.05) between the techniques in the intraocular pressure measurements returned (Goldmann applanation tonometer vs handheld and Goldmann applanation tonometer vs slit lamp-mounted). The Goldmann applanation tonometer measured intraocular pressure 0.34 mmHg higher than handheld and 0.85 mmHg higher than slit lamp-mounted in session 1, and in session 2 Goldmann applanation tonometer intraocular pressure measurement was the same as with the slit lamp-mounted method but lower than with the handheld method by 0.11 mmHg. In PT100 handheld vs slit lamp-mounted comparisons, there were no significant differences (P > 0.05) between intraocular pressure measurements returned by both techniques in sessions 1 and 2. Intrasession and intersession repeatability coefficients for Goldmann applanation tonometer intraocular pressure and slit lamp-mounted intraocular pressure were similar, and better in comparison with those for handheld intraocular pressure.ConclusionThe Goldmann applanation tonometer and PT100 noncontact tonometer in both positions studied here are reliable, consistent techniques for measurement of intraocular pressure, and can be used interchangeably for obtaining intraocular pressure values in young normal subjects. Repositioning of the PT100 tonometer from hand-held to slit lamp-mounted improved its precision and reduced variation with respect to the Goldmann applanation tonometer.

Effects of postural changes on measured intraocular pressure and repeatability of PT-100 tonometer and agreement with applanation and indentation tonometry

“…Previous studies 29,31,48 that compared IOP measurements with the PT-100 and GAT tonometers found no significant differences between the mean IOPs, but only one study 29 had compared measurements with both devices on two separate sessions. The authors found comparable IOP measurements with both instruments.…”

“…Similar to our findings, earlier reports have shown agreement between PT-100 and GAT IOP readings within the normal range of IOP. 22,29,30 In another study that evaluated the performance of the PT-100 tonometer in healthy eyes, the instrument had better repeatability than the GAT. As the LoA between the PT-100 and GAT-measured IOP was within the maximum tolerance range of ±3 mmHg, which was suggested for the validity of a tonometer used to appropriately manage diseases that threaten vision, 39 both tonometers can be used interchangeably in disease management.…”

“…In the first position (HBP-1), the participant was requested to sit upright with the head and neck in the habitual anatomical position and the tonometer was held by hand to measure IOP. 29 The second position replicated the neck flexion or constriction (with a tight necktie), 9 and the participant sat upright with the head and neck in forward head posture (i.e. cervical spine and chin pushed forward so that the ears were anterior to the shoulders) against the chinrest and forehead rest of the slit lamp, whilst the tonometer was mounted on the slit lamp attachment for the second position (HBP-2).…”

“…Although several studies have assessed the precision of IOP measurements made with the ST, 22,26 this study was partly designed to more comprehensively assess the validity of the IOP measurements made with the ST in the light of its resurgence in clinical practice. 22,23,27,28 The PT-100 is a hand-held or slit lamp mounted noncontact tonometer that is widely used in clinics and has been shown to provide IOP readings that compare favourably to the Goldmann applanation tonometer (GAT) within the normal range of IOP, 29,30,31 and in different positions. 29 The repeatability of values measured by an instrument used to collect data for clinical purposes is an important reliability index, especially when it is used to determine and monitor changes in measured ocular parameters over time.…”

“…22,23,27,28 The PT-100 is a hand-held or slit lamp mounted noncontact tonometer that is widely used in clinics and has been shown to provide IOP readings that compare favourably to the Goldmann applanation tonometer (GAT) within the normal range of IOP, 29,30,31 and in different positions. 29 The repeatability of values measured by an instrument used to collect data for clinical purposes is an important reliability index, especially when it is used to determine and monitor changes in measured ocular parameters over time. This is also important when evaluating whether a treatment intervention has any influence on a disease or whether a disease process produces change in measurements.…”