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Editors Selection IGR 13-4

Intraocular pressure: IOP in preterm infants

Comment by Sharon Freedman on:

20424 A longitudinal study to establish the normative value and to evaluate perinatal factors affecting intraocular pressure in preterm infants, Ng PC; Tam BS; Lee CH et al., Investigative Ophthalmology and Visual Science, 2008; 49: 87-92

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Intraocular pressure (IOP) measurement in children poses challenges to clinicians who evaluate and treat pediatric glaucoma, as well as those children at risk for glaucoma. In addition, the normative IOP range in infants and young children may vary significantly from that of healthy adults. Ng et al. (151) present results of a well-designed, prospective, study of intraocular pressure in preterm infants in a single Neonatal Intensive Care Unit (NICU) in Hong Kong. The purpose of this study was to establish a normative range of IOP in these preterm infants, and to identify important perinatal factors that could affect the IOP during the early weeks of neonatal life. Unlike previously published studies, the present study had a longitudinal (rather than cross-sectional) design. The authors enrolled 104 consecutive preterm infants who met the screening criteria for Retinopathy of Prematurity (< 32 weeks of gestational age or birth weight < 1500 grams), or who were moderately premature (32-36 weeks gestational age) and received supplemental oxygen > 7 days. Written consent was obtained for all infants. IOP was measured in awake, calm babies, with topical anesthetic and a speculum in place, before dilation of the pupils, using a handheld applanation tonometer (Tonopen II).

IOP of preterm infants decreases with increasing postconceptional age

Detailed information was recorded regarding the health status of each infant at each visit. Measurements were made at 1, 4, 6, 8, and 10 weeks after birth. Data collection was detailed regarding systemic and health features of each baby at each IOP measurement, and statistical methods were robust.

The authors constructed a percentile chart of IOP in preterm infants, finding median (10th-90th percentile) IOP of 16.9 (12.3-21.5) and 14.6 (10.1-19.2) mmHg at 26.1 and 46.4 weeks post conceptual age, respectively. The most significant finding was that the IOP of preterm infants decreases with increasing postconceptional age. IOP was also negatively associated with mean blood pressure, Apgar score at 1 minute, and use of inhaled corticosteroids, but was positively associated with high-frequency oscillatory ventilation. There was no significant association between IOP and stages of ROP. Despite the limitations of this study (complex medical status of many infants, use of lid speculum to check the IOP, lack of information about central corneal thickness), it does establish a normative IOP range in preterm infants that may facilitate evaluation of those eyes at risk for abnormal IOP elevation from systemic or ocular conditions.

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