Comparison of a new non-contact tonometer with Goldmann applanation

Abstract

with the Goldmann applanation tonometer is reported. Measurements of intra ocular pressure were obtained from 182 eyes of 94 patients. At low pressures «10 mmHg) the candidate tonometer tended to overestimate pressures obtained with the Goldmann tonometer whilst at high pressures (> 19 mmHg) those obtained by Goldmann applanation were underestimated. Between 10 and 19 mmHg there was no significant difference between readings obtained with either method. Up to 71 % of averaged Pulsair measurements fell within ± 3 mmHg of those obtained with the Goldmann tonometer increasing to 78% if pressures �30 mmHg obtained with the Pulsair tonometer were excluded. Adopting a screening criterion of �21 mmHg (Goldmann) resulted in a sensitivity of85% and a specificity of95%. Some evidence that serial Pulsair readings are influenced by the ocular pulse is presented. It is concluded that the Pulsair tonometer can provide clinically useful measurements of intraocular pressure. Clinical measurements of intraocular pressure (lOP) have traditionally been obtained with instruments which require mechanical contact with the cornea; the current instrument of choice and 'gold standard' being the Gold mann applanation tonometer. An alternative method, in which corneal applanation is pro duced by an air pulse, so called 'non-contact' tonometry was first introduced by Grolman1 in 1972 and has several advantages over con ventional applanation; corneal anaesthesia is not required and infection risks are elimi nated.2 However, this instrument does require the patient t6 fixate a target and, like the Goldmann tonometer, is not portable. Recently a new non-contact tonometer (Keeler PulsairTM: Keeler UK Ltd) has been introduced. This instrument requires minimal patient cooperation, is relatively portable and, in common with Grolman's instrument, does not require corneal anaesthesia. Intra ocular pressure is derived from the air pres sure required to produce an applanation event, whilst the precise moment of applana tion is transduced by optical means from changes in corneal reflection. It is not subject to operator error as readings can only be obtained when the instrument is correctly aligned. It can therefore be used by relatively unskilled personnel with minimal training.

Intraocular pressure in an ophthalmologically normal Japanese population

“…Intraocular pressure has been positively correlated with body mass index (BMI) after adjusting for age, gender and BP (Mori et al 2000), and also with increasing degrees of myopia after adjusting for age, central corneal thickness (CCT) and other related factors (Nomura et al 2004). However, these previous studies carried out in Japan measured IOP using non-contact tonometry (NCT), which has relatively low accuracy and is more likely to be affected by CCT than is Goldmann applanation tonometry (GAT) (Moseley et al 1989;Rouhiainen & Terasvirta 1990;Mackie et al 1996;Recep et al 2001;Tonnu et al 2005). In one study, the mean IOP of participants obtained using NCT was reportedly 11.9 ± 2.5 mmHg and 11.5 ± 2.4 mmHg for male and female subjects, respectively (Nomura et al 1999), which was much lower than the mean of 14.5 ± 2.5 mmHg obtained from non-glaucoma participants in an epidemiological study carried out in Japan (Iwase et al 2004).…”

Goldmann applanation tonometry versus non-contact tonometry: a comparative study

“…Many previous studies have also included eyes on anti-glaucoma medications. 1,3,8,10,13 The effect of treatment on the hydration properties of the cornea was overlooked as this was not the aim of the present study.…”

“…Past studies have showed that NCT overestimates IOP at lower values and underestimates at higher values when compared with GAT. [5][6][7][8] Tonnu et al were the only authors to show using the Canon model of NCT that NCT underestimated IOP at lower ranges and overestimated it at higher IOP ranges. 9 Our study showed a correction factor of 0.35mmHg for 10µm change in CCT for both GAT and NCT.…”

Modalities of Tonometry and their Accuracy with Respect to Corneal Thickness and Irregularities

“…The oldest versions of this tonometer showed a fair agreement with GAT (±3 mmHg), but tended to overestimate the IOP for pressures lower than 10 mmHg and underestimate it for values above 19 mmHg. 50 However, modern non-contact tonometers correlate very well with GAT IOP, even though they tend to systematically overestimate it by between 0.12-0.58 mmHg. [51][52][53] With regard to the influence of corneal properties on noncontact tonometry measurements, it is likely that they are more influenced by CCT than GAT.…”

“…The benefits of non-contact tonometry include patient preference, less operator dependence, and no risk of infection transmission. [50][51][52][53] Pneumatonometer (Mentor, Model 30 Classic, Reichert, New York, USA) This is an easy-to-use instrument which provides fast and accurate tonometry readings. Utilizing a pneumatic pump, it can provide real time readings of IOP through a noninvasive applanation method.…”