Optic nerve sheath diameter evaluated by transorbital sonography in healthy volunteers from Pakistan

Objective: Raised intracranial pressure (ICP) is a common manifestation of severe brain injury. Rapid diagnosis and timely intervention is required to prevent secondary brain damage and death. Measurement of optic nerve sheath diameter (ONSD) by ultrasound is increasingly used as a marker to detect raised ICP. Knowledge of normal ONSD in a healthy population is essential to interpret this measurement. We aimed to evaluate normal optic nerve sheath diameter in healthy volunteers in Pakistan. Methodology: It was a prospective, observational study in which one hundred healthy volunteers of Pakistani origin, aged more than 18 years were recruited in the study. The ultrasound probe was placed on the superior and lateral aspect of the orbit against the upper eyelid with the eye closed. For each subject, the primary investigator performed three measurements on each eye. The measurements of each eye were then averaged to yield a mean ONSD. Results: The median ONSD of right eye was 4.84 mm and 95% of individuals had mean ONSD in the range 4.84-4.97 mm while the median ONSD of left eye was 4.86 mm and 95% of individuals had mean ONSD in the range 4.85-4.96 mm. There was no difference among the 3 repeated measures of ONSD in each eye. There was no relationship between ONSD with age, gender and measurement taken between left and right eyes. Conclusion: 95% of study sample have an ONSD less than 4.82 mm. ONSD more than 4.82 mm in this population should be considered abnormal and may reflect raised intracranial pressure.