Comparison of Tono-Pen Avia and Handheld Applanation Tonometry in Primary Congenital Glaucoma

Precis: Tono-Pen AVIA (TPA) intraocular pressure (IOP) values are different from those taken with handheld Goldmann applanation tonometer (GAT) in primary congenital glaucoma (PCG). These differences indicate both tonometers cannot be used interchangeably for measuring IOP in PCG. Purpose: The aim was to compare IOP measurements obtained using TPA and a handheld version of GAT in children with PCG. Materials and Methods: Forty-two eyes from 23 patients were evaluated for central corneal thickness (CCT), axial length, biomicroscopy and IOP measurement with TPA and a handheld GAT under inhalation anesthesia. After 1 eye from each patient was randomized, paired the Student t-test and the Pearson correlation were used for analysis. Generalized linear mixed model was used to estimate the difference between tonometers. Results: Mean age of children was 28.3 +/- 20.5 months. Mean axial length was 24.89 +/- 3.33 mm and mean CCT was 605.9 +/- 81.0 mu m. Mean IOP was 22.1 +/- 9.6 for TPA and 14.0 +/- 4.5 mm Hg for GAT. There was a significant difference of 8.1 +/- 6.9 mm Hg between TPA IOP and GAT IOP (P<0.001). Each 6 months increase in age was associated with 1.32 mm Hg reduction in the difference between tonometers (P=0.002) and each 1 mm Hg higher of mean GAT IOP was associated with -0.73 mm Hg in the difference between TPA and GAT (P=0.002). Also, for every 20 mu m increase in CCT an increase of 1.16 mm Hg in the difference between both devices was expected (P=0.003), after adjustment for potentially confounding variables. Conclusion: There is a significant difference between TPA IOP and GAT IOP in PCG. The difference between TPA and GAT in PCG is influenced by CCT, age and GAT IOP value.