Determination of normal values of optic nerve sheath diameter in newborns with bedside ultrasonography.

Objectives: Bedside sonographic opthalmic ultrasound measurement of optic nerve sheath diameter (ONSD) is an easy, portabl, noninvasive and a radiation free technique to determine increased intracranial pressure. This prospective, multicenter study was aimed to establish the range of normal values for ONSD in preterm and term newborns with a large study population.

Methods: Newborns without intracranial pathology in the Newborn Intensive Care Units and in Obstetrics and Gynecology Departments were enrolled in the study. ONSD was measured at 3 mm distance behind of the right optic nerve head. As 3 mm distance was beyond the optic nerve head in some of the premature newborns, we had also measurements at 2 and 2.5 mm.

Results: ONSD was measured in 554 newborns. Mean ONSD of preterm babies at 2, 2.5 and 3 mm distances were 3.2 ± 0.3 mm (range 2.0-4.2 mm), 3.3 ± 0.3 mm (range 2.2-4.5 mm) and 3.6 ± 0.2 mm (range 2.9-4.5 mm), (p < 0.001, p  < 0.001, p < 0.001) respectively. Mean ONSD of term babies at 3 mm was higher than the mean ONSD of preterm babies in 33 weeks 0 day- 37 weeks 0 days group (p < 0.001). In correlation analysis, a significant, strong and positive correlation was found between ONSD measurements and gestational age, weight, height and head circumference at 2, 2.5 and 3 mm distances.

Conclusion: The normal values reported by the present study may be used for evaluating the ONSD of newborns with different conditions with increased incracranial pressure.