Tonometry
Accurate tonometry is important in the assessment of the pediatric glaucomas, but not always possible, especially in infants and very young children. A normal IOP measurement in newborns ranges from 10 mm Hg to the low teens; by middle childhood, IOP increases to adult levels of 10–21 mm Hg. Glaucoma should be suspected if IOPs are elevated or asymmetric in a cooperative or anesthetized child; in an uncooperative or struggling child, IOP measurements may be falsely elevated.
Table 11-11 Comparisons of Normal Mea sure ments in Pediatric and Adult Eyes
The clinician may be able to successfully measure the IOP of an infant younger than 6 months by performing the measurement while the infant is feeding or immediately thereafter. In this group of patients, IOP can be measured with rebound tonometry (if the infant can be held upright), the Tono-Pen (Reichert Ophthalmic Instruments), pneumotonometry, or a Perkins handheld applanation tonometer, if the palpebral fissure is sufficiently wide.
For children who are relatively cooperative in the clinic but too young for Goldmann tonometry, the rebound tonometer is very useful because it does not require topical anesthesia. This device has been shown to reduce the number of EUAs performed to obtain pressure measurements. However, despite these advantages, initial reports indicate that measurements in patients with congenital glaucoma were higher when taken with the rebound tonometer than when taken with the Perkins tonometer, especially at higher levels of IOP.
General anesthesia is usually required for accurate IOP assessment in older infants (≥6 months) and young children. However, most general anesthetic agents and sedatives unpredictably lower IOP. Exceptions include chloral hydrate, which does not affect IOP; ketamine, which may increase IOP; and midazolam, which has a negligible effect on IOP. In addition, the preparation for general anesthesia may cause infants to become dehydrated, which can reduce IOP. Increased IOP during general anesthesia may result from endotracheal intubation, upward drift of the eyes (Bell phenomenon), or possible induced laryngospasm. It is best to coordinate with the anesthesiologist before the child is brought to the operating room and arrange to take the IOP measurement immediately after induction of general anesthesia (preferably before intubation), which will ideally minimize the effects of anesthesia on IOP. It is also good practice to use the same anesthetic for serial examinations.
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Martinez-de-la-Casa JM, Garcia-Feijoo J, Saenz-Frances F, et al. Comparison of rebound tonometer and Goldmann handheld applanation tonometer in congenital glaucoma. J Glaucoma. 2009;18(1):49–52.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.