In glaucoma care, ophthalmologists are tasked with evaluating various tonometry methods and finding the technologies that provide accurate measurements, while offering a comfortable experience for their patients. But with various devices available, investigators are now exploring whether they offer similar precision. In the case of children with primary congenital glaucoma (PCG), a Journal of Glaucoma study now shows that differences between the Tono-Pen AVIATM (TPA, Reichert Inc.) and a handheld Goldmann applanation tonometer (GAT).
The cross-sectional research investigates 42 eyes of 23 children, mean age 28.3±20.5 months with PCG. Participants underwent biomicroscopic examination, and were assessed for axial length, and central corneal thickness (CCT). The patients’ IOP was measured with both TPA ( and a version of GAT (Draeger tonometer). Tests were performed using sevoflurane inhalation anesthesia. One eye per patient was randomized for statistical analysis.
Tonometry methods returned significantly different results. The mean IOP with TPA was 22.1±9.6 mm Hg, compared with GAT at 14.0±4.5 mm HG. Difference between the instruments was 8.1±6.9 mm Hg (P <.001). In a subgroup of participants with clear, unclouded corneas, mean IOP with TPA was 19.33±9.7 mm Hg, but 12.2±4.3 mm Hg with GAT; a significant difference (P =.001).
When analyzing differences between tonometers based on specific variables, a number of trends emerged based on GAT-determined IOP, CCT, and age of patient. With each 1 mm Hg increase in mean GAT-measured IOP, there was 0.73 mm Hg less difference between the devices (P =.002). After adjusting for factors such as sex, age, axial length (AL), and central corneal leukoma, with every 20 μm greater CCT, there was 1.16 mm Hg more difference between TPA and GAT (P =.003).
Also, for each 6 months older in age, there resulted 1.32 mm Hg less difference between instruments (P =.002). Rigidity may have been a factor. “Although (the) AL effect was clinically significant, but only close to statistical significance (P =.055) it could be reinforcing a trend, as has been previously shown that increasing AL reduces ocular rigidity, thus increasing the variation between IOP measured by devices,” according to the report.
In previous studies, TPA overestimated IOP compared with GAT in a clinic sample not specific to PCG; and another similar devices overestimated IOP in children with PCG and IOPs greater than16 mm Hg, compared with a GAT. Other investigations have associated greater CCT with increased differences between tonometers, affirmed by this analysis.
The investigators measured each participant’s IOP first with GAT, and then after 2 minutes assessed IOP with TPA. This may represent a limitation of the study. Sevoflurane anesthesia is suspected of steadily reducing IOP, especially after 4 to 6 minutes; thus, TPA could have read somewhat lower and further expanded the gap between tools. Still, “the marked difference in values between tonometers recommends caution when trying to transpose the values of both devices,” the analysis explains.
Cronemberger S, Veloso AW. Comparison of Tono-Pen Avia and handheld applanation tonometry in primary congenital glaucoma. J Glaucoma. 2021;30(5):e227-e230. doi:10.1097/IJG.0000000000001820