Noninvasive Ultrasound Assessment of the Normal Optic Nerve Sheath Diameter in Healthy Adults: an Islamabad-based Pakistani Population Study

Author(s): Rubia Ahmad, Aeisha Begum, Salma Umbreen, Ahsen Farooq, Rabia Waseem Butt, Kalsoom Basit

Abstract
Aim: The noninvasive B-mode transocular ultrasound (TOU) measurement of the optic nerve sheath diameter (ONSD) is becoming popular to monitor intracranial pressure (ICP). Different studies report varied values for normal ONSD. Our primary aim was to find the TOU-measured normal ONSD in healthy adult Pakistanis living in Islamabad Capital Territory (ICT).

Methodology: One hundred healthy adult volunteers participated in this cross-sectional study, conducted at the Pakistan Atomic Energy Commission (P.A.E.C.) General Hospital, Islamabad. Each eye was scanned for the optic nerve (ON) via TOU using a B-mode 7-15 MHz linear probe. The investigators measured ONSD in a transverse plane three millimeters behind the retina. They recorded an average of three readings as a mean ONSD value for both eyes.

Results: The overall normal mean ONSD was 4.80±0.26 mm with a minimum of 4.25 mm and a maximum of 5.20 mm. The mean ONSD for the age group of 20-35 years was 4.79±0.27 mm and for 36-50 years, it was 4.81±0.24 mm (p = 0.7952), for the male eye it was 4.83±0.26 mm and for the female eye was 4.75±0.25 mm (p = 0.1238), and for the right eye was 4.79±0.27 mm and for the left eye was 4.80±0.26 mm with (p = 0.2434) and (r = 0.9455). There was no statistically significant difference in the mean ONSD of the four ethnic groups (p = 0.7141).

Conclusion: The normal mean optic nerve sheath diameter in the studied healthy adult Pakistanis, as measured through noninvasive B-mode transorbital ultrasound is 4.80±0.26 mm.