title: Transorbital sonographic evaluation of normal optic nerve sheath diameter in healthy volunteers in Bangladesh.
abstract: BACKGROUND
  Measurement of optic nerve sheath diameter (ONSD) by ultrasound is increasingly used as a marker to detect raised intracranial pressure (ICP). ONSD varies with age and there is no clear consensus between studies for an upper limit of normal. Knowledge of normal ONSD in a healthy population is essential to interpret this measurement.
  
  
  METHODS
  In a prospective observational study, ONSD was measured using a 15 MHz ultrasound probe in healthy volunteers in Chittagong, Bangladesh. The aims were to determine the normal range of ONSD in healthy Bangladeshi adults and children, compare measurements in males and females, horizontal and vertical beam orientations and left and right eyes in the same individual and to determine whether ONSD varies with head circumference independent of age.
  
  
  RESULTS
  136 subjects were enrolled, 12.5% of whom were age 16 or under. Median ONSD was 4.41 mm with 95% of subjects in the range 4.25-4.75 mm. ONSD was bimodally distributed. There was no relationship between ONSD and age (≥4 years), gender, head circumference, and no difference in left vs right eye or horizontal vs vertical beam.
  
  
  CONCLUSIONS
  Ultrasonographic ONSD in Bangladeshi healthy volunteers has a narrow bimodal distribution independent of age (≥4 years), gender and head circumference. ONSD >4.75 mm in this population should be considered abnormal.
authors: Mahidol-Oxford Tropical Medicine Research Unit, Rajthewi, Bangkok, Thailand.
authors: Rapeephan R
authors: RR
authors: Maude
authors: Md Amir
authors: MA
authors: Hossain
authors: Mahtab Uddin
authors: MU
authors: Hassan
authors: Sophie
authors: S
authors: Osbourne
authors: Katherine Langan Abu
authors: KL
authors: Sayeed
authors: Mohammed Rezaul
authors: MR
authors: Karim
authors: Rasheda
authors: R
authors: Samad
authors: Shyamanga
authors: S
authors: Borooah
authors: Bal
authors: B
authors: Dhillon
authors: Nicholas P J
authors: NP
authors: Day
authors: Arjen M
authors: AM
authors: Dondorp
authors: Richard J
authors: RJ
authors: Maude
mesh_terms: D000293:Adolescent; D001459:Bangladesh; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D014463:Ultrasonography