Título

Transorbital Sonographic Evaluation of Normal Optic Nerve Sheath Diameter in Healthy Volunteers

Introdução

Measurement of optic nerve sheath diameter (ONSD) by ultrasound is increasingly used as a marker to detect raised intracranial pressure (ICP). However, there is no clear consensus about the normal ONSD in a healthy population in Brazil. The purpose of the present study was to determine the optic nerve sheath diameter (ONSD) in normal adults from Rio de Janeiro, Brazil.

Método

In this cross-sectional study, ONSD was measured using a 10 MHz ultrasound probe in healthy volunteers from Rio de Janeiro, Brazil. All subjects were aged 18 years or older and had no history of neurological diseases. Patients with glaucoma were also excluded. A single investigator used a 12 MHz linear ultrasound probe (Sonomed) oriented perpendicularly in the vertical plane and at around 30 degrees in the horizontal plane on the closed eyelids of both eyes of supine subjects. Ultrasound gel was applied to the outside of eyelid and recordings made in the axial and longitudinal planes of the widest diameter visible. Video of every ultrasound was recorded for later analysis by a single blinded investigator. To determine ONSD, electronic calipers were used to mark 3 mm perpendicularly behind the retina. Continuous data were presented as means with standard deviations.

Resultados

46 subjects were enrolled, mean age was 66± 18 years (range 24 – 84 years), 67 % were female. Median ONSD was 3.4 mm and mean ONSD was 3.46mm ± 0.43mm, ranging from 2.69 to 4.3mm. There was no relationship between ONSD and age or gender.

Conclusões

The normal reference values obtained for ONSD measurements can serve as diagnostic aid in appropriate clinical settings. The results showed no significant correlation with age or gender, thus allowing for local use of the uniform reference values for both genders in adults. Evaluation of intracranial pressure is a difficult task in patients with intracranial space occupying diseases as a consequence of head trauma, hemorrhage, or ischemia. The use of invasive devices remains the gold standard for measuring intracranial pressure in comatose or sedated patients. Different studies document that elevated intracranial pressure leads to an enlargement of the ONSD. Previous studies have found that transorbital B-mode sonography is a feasible method to assess the ONSD with a high intra and interobsever reliability.