Comparison of Scleral Tono‐Pen Intraocular Pressure Measurements with Goldmann Applanation Tonometry

SIGNIFICANCE: Measuring the intraocular pressure (IOP) on the sclera can be an alternative to conventional corneal measurement in eyes with scarred corneas. However, these measurements have to be evaluated prior in normal eyes. Our study aimed to evaluate scleral IOP using Tono-Pen and compared it with corneal Goldmann applanation measurements. PURPOSE: The aim of this study was to evaluate the ability of limbal and scleral Tono-Pen IOP readings to predict central corneal Goldmann applanation tonometry (GAT) readings in eyes with normal corneas. METHODS: In a cross-sectional study, 115 eyes of 115 patients attending a tertiary eye care center underwent GAT on the central cornea followed by Tono-Pen readings at the central cornea, at the limbus, and at the sclera. Bland-Altman plots were used to determine the agreement between different methods of IOP measurement. RESULTS: The median IOP (interquartile range) by GAT performed on the central cornea was 18 (16, 24) mmHg, and the IOP ranged from 10 to 54 mmHg. The median IOPs (interquartile range) by Tono-Pen obtained at central cornea, limbus, and sclera were 16 (13, 23), 23 (17, 28), and 33 (27, 44) mmHg, respectively. The Pearson correlation coefficient and the 95% limits of agreement between GAT readings and Tono-Pen readings at the central cornea were 0.9 (P < .001) and -4.9 to 8.74 mmHg, respectively. The correlation coefficient between GAT readings and Tono-Pen readings at the limbus and GAT readings and Tono-Pen readings at the sclera was 0.46 (P < .001) and 0.23 (P = .01), respectively. The 95% limits of agreement between these pairs of readings were -20.55 to 13.66 and -44.02 to 13.37 mmHg, respectively. CONCLUSIONS: This study showed limited ability of Tono-Pen readings obtained at the limbus and sclera to predict the central corneal GAT IOP readings in eyes with normal corneas at various IOP ranges.