Can Corneal Biomechanical Properties Explain Difference in Tonometric Measurement in Normal Eyes?

International comparisons of intraocular pressures, as measured by Tono-Pen and Goldmann applanation tonometry, in healthy adults: A meta-analysis

BACKGROUND

Investigate intraocular pressure (IOP), as measured by Tono-Pen (TP) and Goldmann applanation tonometry (GAT), in healthy adults. Provide an updated synthesis of multinational, primary studies, reported during the 10-year period 2011 to 2021 and offer an evidence-based benchmark, against which IOP can be evaluated across subject variables and pathologies. Three primary research questions are investigated: Is there a statistically significant difference between IOP measured by TP and GAT? If yes, is the difference clinically significant? Is measurement of IOP affected by the country or setting location, in which the measurements are made?

METHODS

An aggregate meta-analysis was conducted on 22 primary studies, from 15 different countries. IOP measurements were made from each healthy adult subject, with both the TP and GAT. Primary studies were identified and data extracted according to recommended preferred reporting items for systematic reviews and meta-analysis protocol guidelines. Meta-analysis summary results are reported as the point estimate of the raw mean difference of IOP.

RESULTS

Meta-analysis reveals a statistically significant difference in raw mean differences in IOP, when measured by TP and GAT, in the healthy adult population. Tono-Pen IOP measurements are higher than GAT IOP measurements. The point estimate for the summary effect size = -0.73 mm Hg, P = .03. The prediction interval for the true effect size, in 95% of all comparable populations, is -4.03 to 2.58 mm Hg. There is no clinically significance difference in IOP when measured by TP and GAT. Meta-regression analysis reveals statistically significant differences in measurement of IOP by countries, R2 analog = 0.75, P = .001. There is no statistically significant difference in measurement of IOP as a function of measurement location setting, R2 analog = -0.17, P = .65.

CONCLUSIONS

IOP measured by TP are marginally higher compared to GAT, in the healthy adult population. However, from a clinical practice perspective, TP and GAT produce similar IOP measurements. There is evidence of significant variabilities in IOP measurements as a function of country. IOP measurements collected in a research laboratory setting are similar to IOP collected in a clinical setting. Results have implications for the primary care physician requiring a portable, inexpensive, reliable, and easily administered instrument to assess IOP.

Repeatability, reproducibility, agreement, and safety of Tono-Pen tip cover for intraocular measurement using latex and polyethylene wrap

PURPOSE

To evaluate repeatability, reproducibility, and agreement of intraocular pressure measurement with Tono-Pen using Ocufilm and polyethylene wrap tip cover in human eyes.

METHODS

This is a cross-sectional, experimental study. A gas-sterilized, polyethylene wrap was used as an alternative for Tono-Pen tip cover. For the right eye, 4 measurements using polyethylene wrap tip cover were done by two examiners (A and B) in random order to assess intra-observer repeatability and inter-observer reproducibility. For the left eye, 4 measurements were done by examiner A using both polyethylene wrap tip cover and Ocufilm in random order to assess intra-observer repeatability and agreement. Bland-Altman plot and intraclass correlation coefficient (ICC) were used in all analyses. Cost minimization analysis was evaluated.

RESULTS

For examiner A, the repeatability of polyethylene wrap tip cover was -0.34, 95% limits of agreement (LOA) were -3.04 to 2.36, and ICC was 0.93 in the right eyes. As for the left eyes, the repeatability of polyethylene wrap tip cover was -0.33, 95% LOA were -3.01 to 2.36, and ICC was 0.93. For examiner B, the repeatability of polyethylene wrap tip cover was -0.02, 95% LOA were -2.88 to 2.83, and ICC was 0.92. The inter-observer reproducibility of polyethylene wrap tip cover was 0.36, 95% LOA were -3.34 to 4.07, and ICC was 0.90. The repeatability of Ocufilm was -0.42, 95% LOA were -2.75 to 1.91, and ICC was 0.95. The agreement of polyethylene wrap tip cover and Ocufilm was -0.71, 95% LOA were -5.18 to 3.76, and ICC was 0.83. There were no allergic reactions or serious complications. From the cost minimization analysis, the local cost for polyethylene tip cover was approximately 8 times lower compared to Ocufilm.

CONCLUSIONS

Tono-pen with Ocufilm and polyethylene wrap tip cover were used to measure the intraocular pressure. The polyethylene wrap tip cover demonstrated acceptable repeatability, reproducibility, and agreement with Ocufilm in normotensive eyes, and had a good safety profile.

Determining Significant Elevation of Intraocular Pressure Using Self-tonometry

SIGNIFICANCE

Icare HOME rebound tonometry is increasingly adopted into clinical practice for IOP phasing of glaucoma patients and suspects. Because of measurement differences with applanation tonometry and diurnal fluctuations, interpretation of the IOP measured with Icare HOME phasing can be challenging.

PURPOSE

The purpose of this study was to use a large patient cohort to develop a practical, analytical tool for interpreting Icare HOME measurements with respect to applanation pressure.

METHODS

IOP measurements using the Icare HOME and an applanation tonometer were taken prospectively in 498 consecutive patients. Bland-Altman, frequency distribution, and linear regression analysis were applied to determine measurement differences. A novel criterion, Threshold Icare HOME IOP, was developed to assist identification of elevation above target applanation pressure, considering the expected diurnal variation and measurement variability.

RESULTS

Icare HOME tended to underestimate applanation tonometry (mean bias, -1.7 mmHg; 95% limits of agreement, -7.0 to +3.6). Overall, differences were within ±3 mmHg in 71.5% and ±5 mmHg in 92% of patients. Based on the novel criterion developed, Icare HOME measurements that exceed target applanation pressure by 6 mmHg or greater are generally outside the 95% limit of expected observations.

CONCLUSIONS

The Threshold Icare HOME IOP is a novel and practical criterion that can assist clinicians in their interpretation of Icare HOME phasing measurements with respect to target applanation pressures. Elevation above the expected thresholds may prompt closer monitoring or even modifications to glaucoma management.

A Review of the Use of Confidence Intervals for Bland-Altman Limits of Agreement in Optometry and Vision Science

SIGNIFICANCE

Confidence intervals are still seldom reported for Bland-Altman 95% limits of agreement. When they are reported, 50% of articles use approximate methods and 50% use exact methods.

PURPOSE

Bland-Altman limits of agreement can be unreliable estimates, especially for small sample sizes. However, authors seldom use confidence intervals for limits of agreement. This article reviews their use in Optometry and Vision Science.

METHODS

A keyword search for "Bland," "Altman," "Bland-Altman," "LoA," and "limits of agreement" was conducted on the Optometry and Vision Science website within a time range from January 2016 to December 2018.

RESULTS

Fifty articles were reported or were judged to use Bland-Altman analysis; sample sizes ranged from 3 to 2072. Eight of these article reported confidence limits for limits of agreement, four of which used exact methods and four used Bland and Altman's approximate method.

CONCLUSIONS

Use of confidence intervals for limits of agreement has increased in Optometry and Vision Science but is far from universal. To assist researchers in calculating exact confidence limits for Bland-Altman limits of agreement, spreadsheets are included for performing the calculations and generating Bland-Altman plots with the confidence intervals included.