A comparison of Icare PRO and Tono-Pen XL tonometers in anesthetized children

BACKGROUND Tonometry in the anesthetized child, vital for evaluating known or suspected glaucoma, remains limited to tonometers capable of supine recording. The Icare PRO measures intra-ocular pressure (IOP) in the sitting or supine patient. The purpose of this study was to compare Icare PRO and Tono-Pen tonometry during examination under anesthesia in eyes of supine children with normal eyes and glaucoma and/or corneal pathology. METHODS In this prospective study of children undergoing examination under anesthesia, IOP was recorded in both eyes with Icare PRO and Tono-Pen immediately after mask anesthesia induction, with instrument order randomized. RESULTS A total of 100 eyes of 50 children (median age, 58 months) were included. IOP range was 6-50 mm Hg by Icare PRO and 6-53 mm Hg by Tono-Pen. Mean IOP measured by Tono-Pen (18.9 +/- 7.5) was higher than that measured by Icare PRO (16.7 +/- 7.1 mm Hg) by 2.2 mm Hg (P < 0.001). The presence of corneal edema was associated with IOP measurements higher by Tono-Pen than by Icare PRO (mean difference, 8.4 mm Hg). When eyes with corneal edema were excluded from analysis, there was no correlation between central corneal thickness and the difference in IOP between the two instruments. CONCLUSIONS IOP in eyes of supine children under anesthesia measured approximately 2 mm Hg higher by Tono-Pen than Icare PRO and this difference was greater in eyes with frank corneal edema. Icare PRO may become a valuable tool for tonometry in supine infants and children, but a confirmatory test should be considered in eyes with corneal edema.