Comparison of Optic Nerve Sheath Diameter between both eyes: A Bedside Ultrasonography Approach.

Context: Optic nerve sheath diameter (ONSD) has long been accepted as a reliable proxy of intracranial pressure especially in critical care and bedside settings. The present consensus is to measure ONSD in both eyes and take average value, which is cumbersome and a potential cause of discomfort to the patient.

Aim: We aim to compare the values of ONSD of the right and left eye in a random sample as measured by bedside ocular ultrasonography (USG) in Indian adults.

Settings and Design: This was a prospective study conducted from September 2012 to March 2013 in the Department of Internal Medicine of a tertiary care hospital situated at moderate high altitude (11,500 ft) in India.

Materials and Methods: Patients admitted with high altitude pulmonary edema (HAPE) were recruited by convenience sampling. The ONSD of both eyes were measured 3 mm behind the globe using a 7.5 MHz linear probe on the closed eyelids of supine subjects.

Statistical Analysis: Analysis was done using SPSS 17.0.

Results: A total of 47 patients of HAPE were recruited to the study with daily ONSD recording of both eyes during the admission period. The mean ONSD of the left eye was 4.60 (standard deviation [SD] = 0.71) whereas the mean ONSD of right eye 4.59 (SD = 0.72). The ONSD of the right eye and left eye was strongly correlated (correlation coefficient = 0.98 with P < 0.0001). The mean difference in the ONSD of both eyes (right-left) was -0.0044 (SD = 0.11) which was not statistically significant ( P = 0.533).

Conclusion: Our results suggest that the difference in ONSD of both eyes is not statistically significant in disease or health. This study also suggests that the ONSD of either eye can be predicted by the other eye recordings. Based on these findings, it can be suggested that during ocular USG for routine bedside/research purposes it is sufficient to measure ONSD of any of the one eye to save time and avoid discomfort to the patient.