Uday Kumar Jaihind Khasage1, Vijaya Kumar2, Narendra Sharanappa Shamanur3, Bakkesh Budhihal Prasad4, Bharath Kempanna5, Ganesha Billahalli Siddappa6, Ashray Vasanthapuram7, Sachin Nayak Sujir8
BACKGROUND
Optic nerve sheath ultrasonography provides a very promising bedside tool for the detection of raised ICP. Since the optic nerve is a part of the central nervous system, it is surrounded by Cerebrospinal Fluid (CSF).1 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.2-4
The aim of the study is to measure the optic nerve sheath diameter in normal individuals using bedside ultrasonography in both eyes. To categorise the variations in optic nerve sheath diameter according to individual eye, age, sex and to evaluate any of the parameters, which will have influence on the variations.
MATERIALS AND METHODS
This was a prospective observational study on normal population with sample size of 500. Data was obtained from measuring ONSD from normal individuals with no symptoms or signs of raised intracranial tension (healthy volunteers). The measurements was taken by using a 7.5 MHz linear ultrasound probe and measurements were taken 3 mm posterior to the optic disc. Measurements each subject had the ONSD from both eyes measured twice and an average taken for each eye. The results obtained were correlated for variations across the individual eyes, age groups and sex of the individual by using appropriate statistical analysis.
RESULTS
Total of 500 subjects were enrolled in our study. Of that, 280 (56%) were males and 220 (44%) were females. The mean ONSD obtained separately for males, females according to age distribution for each eye. There was not much deviation from the standard value for each of different eyes or age groups. Mean ONSD for males 4.5-5.2 (4.8±0.3 mm) and females 4.7-5.1 (4.9±0.2 mm).
CONCLUSION
Standard reference value for normal optic nerve sheath diameter by using ultrasound in southern part of India can be taken between 4.5 to 5.2 mm. It has been observed in our study that the standard value doesn’t change much with the age or gender.
