Intraocular pressure asymmetry in a population tested with the Pulsair non-contact tonometer

Distribution of intraocular pressure in healthy Iranian children: the Shiraz Pediatric Eye Study

PURPOSE

To describe the mean and normal range of intraocular pressure (IOP) and its associations in healthy Iranian school children using the noncontact tonometer.

METHODS

In this cross-sectional study as part of the Shiraz Pediatric Eye Study, a stratified random sampling was performed among elementary school children of Shiraz, Iran. Basic demographics and socioeconomic status of households, past medical history, drug history, and eye health history were collected for each eligible student. Children underwent complete ophthalmic examination. Axial length, corneal curvature, and anterior chamber depth were measured using the IOL-Master 500.

RESULTS

Of 2,001 eligible children, 1,901 (95.0%; 3,802 eyes) with a mean age of 9.1 ± 1.6 years (standard deviation; range, 6-12 years) had reliable IOP. The mean spherical equivalent refraction was 0.5 ± 1.3 D for the right eye and 0.6 ± 1.2 D for the left eye. Mean IOP in the right eye was 15.1 ± 2.5 mm Hg (median, 15.0; range, 8.0-27.0 mm Hg); in the left eye, 15.2 ± 2.5 mm Hg (median, 15.0; range, 9.0-28.0 mm Hg). In multiple regression analyses, the mean IOP was significantly lower among asthmatic children compared to normal participants (P = 0.007). The measured IOP was significantly higher in myopic participants than hyperopic patients (P = 0.003).

CONCLUSIONS

This study provides a useful normative IOP database using the noncontact tonometer for healthy Iranian school children.

Systematic bias in real-world tonometry readings based on laterality?

AIMS

In research settings, the first eye examined tends to have a higher intraocular pressure (IOP) than the second. We sought to verify whether clinicians in Yorkshire, UK, measure IOP in right eyes before left and whether such behavioural factors affect IOP readings at the population level.

METHODS

We observed 128 IOP measurements taken by 28 ophthalmologists using Goldmann applanation tonometry (GAT) over a 4-month period in 2018, recording which eye was examined first. All IOP measurements on electronic patient records for Leeds Teaching Hospitals NHS Trust, UK, between January 2002 and June 2017 were extracted, yielding IOP readings for 562,360 eyes, analysed for evidence of systematic bias in IOP measurement.

RESULTS

Right eye IOP was measured before left in 112/128 observations (87.5% (95% CI: 75.2%-94.2%)). For IOP measured by GAT, there was no statistically significant difference (p = 0.121) between right and left eye IOP (mean IOP 16.95 and 16.96 mmHg, respectively). Even values of IOP were reported more frequently than odd values (136,503/214,628 (63.6%) were even). Identical IOP readings for both eyes were recorded in 124,392/254,380 patients (48.9%) who had both eyes measured.

CONCLUSIONS

Our study found no IOP difference based on laterality, but strong evidence of certain trends associated with IOP measurement by GAT, such as a preference for even values and the same IOP being recorded for both left and right eyes. Such effects may be explained by behavioural aspects of GAT and suggest that there are substantial opportunities for improvement in the way GAT is utilised in real world settings.

Factors associated with fluctuations in repeated measurements of intraocular pressure using the Goldmann applanation tonometer in Japanese patients with primary open-angle glaucoma

Purpose

The aim of this study was to determine whether fluctuations in intraocular pressure (IOP) occur as a result of the order of IOP measurements or successive IOP measurements in patients with glaucoma and, if so, identify the factors causing these fluctuations.

Patients and methods

Four hundred twenty-eight eyes of 214 Japanese patients with primary open-angle glaucoma (POAG) were enrolled. Patients treated with beta-blockers or prostaglandin analogs alone were included. Additionally, in the IOP measurements by noncontact tonometer, the same cases of IOP of the right and left eyes prior to this study were included in this study. Four successive IOP measurements were carried out using a Goldmann applanation tonometer as follows: IOP was measured in the first eye (right or left) and then in the fellow eye and IOP was again measured in the first eye and then in the fellow eye. Repeated-measures analysis of variance was used to test the differences in IOP between successive measurements. Generalized linear mixed models were used to test differences in IOP measurements between the right and the left eyes on repeated applanation tonometry and according to the order of measurement. Conditional binomial logistic regression analysis was used to identify factors associated with fluctuating repeated applanation tonometry measurements. A P-value of <0.05 was considered statistically significant.

Results

IOP values decreased significantly according to the number of measurements (13.8–13.0; P<0.001–0.036, respectively). There was no significant difference in IOP measurements between the right and left eyes. The first IOP measurement was significantly higher than the fourth measurement (P=0.038); however, there was no significant difference between other combinations. The use of a prostaglandin analog was the only significant contributor to fluctuating IOP measurements (P=0.002).

Conclusion

IOP measured in the first eye, either right or left, was higher than that measured in the fellow eye in Japanese patients with POAG. The use of a prostaglandin analog may be associated with fluctuating IOP on repeated applanation tonometry.

Distribution of IOP measured with an air puff tonometer in a young population

Purpose

To determine the normal range of intraocular pressure (IOP) in the young and its association with certain corneal parameters using a non-contact device.

Methods

Subjects were selected from students of Mashhad University of Medical Sciences through stratified sampling. All participants had visual acuity testing, corneal imaging, a comprehensive slit-lamp examination by an ophthalmologist, and IOP measurement using a non-contact air-puff tonometer.

Results

Of the 1280 invitees, 1073 (83.8%) participated, and 1027 were eligible. Mean IOP was 16.38 mmHg [95% confidence interval (CI): 16.22–16.53] in the total sample, 16.14 mmHg (95% CI: 15.84–16.45) in men, and 16.48 mmHg (95% CI: 16.31–16.66) in women. There was a significant IOP difference between myopes and emmetropes (P = 0.031). Based on the multiple linear regression model, IOP associated directly with age and central corneal thickness (CCT), and inversely with corneal diameter, spherical equivalent (SE), and keratoconus. Based on standardized coefficients of the regression model, CCT and SE had the strongest association with IOP.

Conclusions

In the present study, we demonstrated the IOP distribution in a young population using a non-contact method. CCT and SE were strongly associated with IOP.

The accuracy and clinical application of predictive models for primary open-angle glaucoma in ocular hypertensive individuals

OBJECTIVE

This report compares the accuracy of 3 prediction models for the development of primary open-angle glaucoma (POAG). The models differ primarily in their handling of these eye-specific variables: intraocular pressure (IOP), central corneal thickness (CCT), vertical cup-to-disc ratio (VCD), and visual field pattern standard deviation (PSD). The "means" model includes age and the means of right and left eyes; the "means plus asymmetry" model includes age, the means of right and left eyes as well as the absolute difference between eyes for eye-specific variables; and the "worse" eye model includes age and values from the eye at higher risk for developing POAG.

DESIGN

This report uses data from the observation group of the Ocular Hypertension Treatment Study (OHTS) and the placebo group of the European Glaucoma Prevention Study (EGPS) who have complete data on both eyes at baseline. Performance of the prediction models is assessed using the c-statistic, calibration chi-square, and Pearson correlation coefficient.

PARTICIPANTS

The OHTS observation group (n = 717; 6.7 years median follow-up) and the EGPS placebo group (n = 324; 4.9 years median follow-up).

TESTING

Baseline data included demographic characteristics, medical history, ocular examination, visual fields, and optic disc photographs.

MAIN OUTCOME MEASURES

Development of reproducible visual field abnormality or optic disc deterioration as determined by masked readers and attributed to POAG by a masked end point committee.

RESULTS

Baseline factors that were statistically significant in all predictive models were age, IOP, CCT, VCD, and PSD. Also, statistically significant were baseline asymmetry in IOP and asymmetry in VCD. The c-statistics for the "means" model, "means plus asymmetry" model, and "worse" eye model were 0.74, 0.77, and 0.75, respectively. The calibration chi-square values were 7.32, 11.19, and 1.81, respectively. Correlation coefficients between risk estimates calculated by different models ranged from 0.94 to 0.98.

CONCLUSIONS

The high agreement between the risk estimates from 3 different predictive models for the development of POAG suggests little difference in their statistical or clinical performance. The predictive model that uses the means of both eyes for eye-specific variables is the simplest to use and the most robust to measurement variability and error.

Variation of 24-hour intraocular pressure in healthy individuals: right eye versus left eye

PURPOSE

An assumption for the one-eye therapeutic trial of ocular hypotensive drugs is the symmetrical variation of intraocular pressure (IOP) between the two eyes. We evaluated whether or not 24-hour variations of IOP in the two eyes are similar in healthy individuals.

DESIGN

Experimental study with human subjects.

PARTICIPANTS

Ninety-one healthy individuals.

METHODS

We reviewed bilateral IOP data collected from 38 younger (18-25 years) and 53 older (40-74 years) experimental subjects housed for 24 hours in a sleep laboratory. Intraocular pressure was measured every 2 hours using a pneumatonometer in the sitting and supine positions during the 16-hour diurnal/wake period and in the supine position during the 8-hour nocturnal/sleep period. Measurements were always taken first in the right eye. For each age group, the two eyes' means, peaks, troughs, and ranges of IOP during office hours, the diurnal period, the nocturnal period, and the 24-hour period were compared. The coefficient of determination was used to examine the strength of association between the right and left IOPs.

MAIN OUTCOME MEASURES

Bilateral IOP.

RESULTS

For each age group, the profiles of IOP variations were similar in the two eyes with either the habitual body positions (diurnal sitting and nocturnal supine) or the 24-hour supine position. Mean, peak, and trough IOPs in the right eye were slightly higher than those in the left eye during the defined periods. There was no difference in the IOP range, except for the supine IOP in the younger group during the diurnal period. Cosine fits of the 24-hour supine IOP indicate no difference in the estimated phase timing or the 24-hour variation between the two eyes. Coefficients of determination for single pairs of right and left IOPs were in the range of 0.311 to 0.741.

CONCLUSION

Variations of 24-hour IOP in the right and left eyes are similar. However, because the strength of association between the two eyes is only moderate, it may be difficult to perform a one-eye therapeutic trial using single pairs of right and left eye IOP measurements.

[Comparative study of pneumotonometer and Goldmann tonometer for screening high intraocular pressure in primary care]

OBJECTIVE

Evaluation of reliability of measurements of IOP obtained with air-puff noncontact tonometer respect the obtained with the conventional Goldmann tonometer. As well, analysis of the possibility of a higher difference between the measurements by both methods respect the fact of being myope or hypermetrope.

DESIGN

Comparative study of two measurement methods.

SETTING

General ophthalmology clinic and primary care clinic of our sanitary area.

PATIENTS

Aleatory sample among the patients who went to the general ophthalmology clinic for any cause from the first of May to the thirtieth of June of 1996. The patients with predisposing processes for glaucoma were excluded, as well as those who suffered ocular surgery or those who took drugs which influenced the IOP.

INTERVENTIONS

The ophthalmologist made three measurements of IOP in each eye and the sight of all the patients were tested. The arithmetic average was made among every three measurements. The physician of primary care made three measurements of IOP in each eye with the air-puff noncontact tonometer, and the arithmetic average was made.

RESULTS

81 patients were included, from whom 7 presented high IOP. The sensibility of the air-puff noncontact tonometer, compared with Goldmann tonometer, was 86% (95% CI, 18.20-99.63%), and the specificity 84% (95% CI, 89.66-78.08%). The air-puff noncontact tonometer obtained measurements between 1.116 and 2.008 mmHg higher than the Goldman tonometer. This difference, worthless from the clinic point of view, didn't find a relationship with the fact of being myope or hypermetrope. It was found a positive lineal association between the measurements made by both methods, with a correlation coefficient of 0.8086 (p < 0.001, 95% CI, 0.7476-0.8560).

CONCLUSIONS

The results obtained are similar to the ones of other published series. A tendency of higher measurements with the air-puff noncontact tonometer is observed. It hasn't been observed a higher difference between both methods in myopes. The air-puff tonometer is a valid reliable technique to be used in primary care, it is easy to use, it doesn't transmit infectious illnesses, and it isn't necessary to use anaesthetic or staining eyedrops.

Reproducibility with the Keeler Pulsair 2000 non-contact tonometer

AIMS

The IOP variation on repeated testing with the recently introduced Keeler Pulsair 2000 instrument was investigated.

METHODS

One hundred normal individuals (50 male and 50 female) new to the instrument had three sets of IOP recordings within a 15 minute time period.

RESULTS

The mean of the first set of IOPs from both right and left eyes was significantly higher than those from subsequent sets (p < 0.0001 for right eyes and p = 0.01 and < 0.0002 for left eyes). This tendency increased significantly with increasing IOP. Second and third IOP sets were, however, similar indicating stabilisation of IOP measurements. The coefficient of repeatability of the instrument between second and third sets was 4.2 mm Hg for right eyes and 3.6 mm Hg for left eyes.

CONCLUSION

The Pulsair 2000 passes the British standard for reproducibility of a standard test method.

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

The difference in intraocular pressure (IOP) between the highest and lowest measurements on an eye with noncontact tonometry (the range) has been reported to be less than 4 mmHg in most normals. The range of IOP to be expected with the Keeler Pulsair in normals over the age of 50 years was determined by analysing the results of IOP 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 analysis indicated that this was not due to an erroneously high first pulse in a set of four, and that IOP asymmetry previously reported when screening females is due to a generalised tendency for IOPs in right eyes to measure higher than those recorded in the left. The occurrence of a range of IOP recordings up to 10 mmHg in an eye is relatively common with the Pulsair and individuals undergoing glaucoma screening with this instrument should not be referred purely on the basis of a large IOP range.