Comparison of Goldmann applanation tonometer, Tono-Pen and noncontact tonometer in children

BACKGROUND: To evaluate the agreement of Goldmann applanation tonometer (GAT) with Tono-Pen and noncontact tonometer (NCT) for measurement of intraocular pressure (IOP) in pediatric age group and to evaluate the correlation between central corneal thickness (CCT) and IOP measured with the tonometers used. MATERIALS AND METHODS: IOP was measured in 200 eyes in a group of Indian children, aged between 8 and 18 years using three different tonometers: NCT, the Tono-Pen and GAT. All IOP readings were made in the office settings by the same examiner. Readings obtained were compared between the instruments and with the CCT for each tonometer. Tonometer inter-method agreement was assessed by the Bland–Altmann method. The relations of CCT with absolute IOP values and inter-tonometer differences were analyzed by linear regression. RESULTS: The mean age was 13.37 ΁ 3.51 years. The mean IOP values recorded with NCT; Tono-Pen and GAT were 14.38, 15.63, and 12.44 mmHg, respectively. Both Tono-Pen and NCT recorded statistically higher IOP values than the GAT (P = 0.00) regardless of the CCT. The percentage increase of IOP measured over GAT was 15.66% for NCT and 25.70% for Tono-Pen which was also statistically significant. A correlation was found between CCT and IOP values obtained with all the three tonometers. CONCLUSION: IOP measurements on children vary significantly between instruments and correlations are affected by the corneal thickness. Further studies on children are needed to determine which instrument is most appropriate and to derive a normative IOP scale for the growing eye.