Comparison of the iCare, Tono-Pen, non-contact airpuff, and Goldmann applanation tonometers in eyes with corneal edema after penetrating keratoplasty

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.

Intraocular Pressure Measurement after Penetrating Keratoplasty

Assessing the intraocular pressure is a difficult but crucial task in the follow-up of patients that have undergone penetrating keratoplasty. Early recognition of elevated intraocular pressure and/or glaucoma and establishment of the appropriate treatment is essential to ensure the best possible visual outcome for patients dealing with this feared complication. Although Goldmann applanation tonometry is still the gold standard for measuring the intraocular pressure, its limitations in postkeratoplasty eyes, due to postoperative modified corneal morphology, have led to the search for more suitable alternatives. This review is the result of a comprehensive literature search in the MEDLINE database that aims to present glaucoma in the context of perforating keratoplasty, the corneal properties with impact on ocular pressure measurement, and the results achieved with the most important tonometers that have been studied in this pathology. Goldmann applanation tonometry remains the reference for intraocular pressure assessment even in corneas after penetrating keratoplasty. However, some promising alternatives have emerged, the most important of which are the Pascal dynamic contour tonometry, the Tono-Pen XL, the ocular response analyzer, and the iCare. All have advantages and disadvantages but have proved to be appropriate alternatives, especially in cases in which Goldmann applanation tonometry cannot be used.

Rebound tonometry by iCare 200 (IC200): comparison with Tono-Pen in the operating room and Goldmann applanation in the clinic

BACKGROUND

Tonometry guides decision making in children with known or suspected glaucoma. The iCare IC200 is a recently FDA-approved rebound tonometer that can measure intraocular pressure (IOP) in both supine and upright patients. The purpose of this study was to evaluate this new tonometer against more commonly used standard instruments: Tono-Pen in the operating room (OR arm) and Goldmann applanation in the clinic (clinic arm).

METHODS

The OR arm included sequential children undergoing general anesthesia. The clinic arm included cooperative children seen in clinic. IOP was measured twice (right eye then left eye, repeat) with IC200 and either Tono-Pen (OR arm) or Goldmann (clinic arm).

RESULTS

A total of 99 children were included: 75 for the OR arm and 24 for the clinic arm. There was a strong correlation between the IOP measured by IC200 and each device (R² = 0.81 for Tono-Pen; R² = 0.78 for Goldmann). In the OR arm, the overall mean IOP difference (ΔIOP [Tono-Pen - IC200]) was -1.6 mm Hg. For eyes with corneal edema (n = 12), ΔIOP ranged from -8 to 15 mm Hg. At IOP >20 mm Hg, mean ΔIOP was -3.7 mm Hg. In the clinic arm, the mean ΔIOP (ΔIOP [Goldmann - IC200]) was -1.2 mm Hg.

CONCLUSIONS

In eyes of children under general anesthesia with IOP <20 mm Hg without corneal edema, IC200 and Tono-Pen correlated well. In cooperative clinic patients, Goldmann and IC200 correlated well over the range of IOP studied.