Objectives: The diagnosis of raised intracranial pressure is very crucial in critically ill patients. The optic nerve sheath (ONS) is in continuum with the subarachnoid space thus, an increase in ICP will result in a corresponding increase in the optic nerve sheath diameter. Ideally the best method to measure intracranial pressure is invasive intracranial devices but, in many situations, direct ICP monitoring or even imaging of the brain is not possible. In such conditions immediate diagnosis and intervention proves to be lifesaving. Hence optic nerve sheath diameter assessment by ultrasonography (US-ONSD) is emerging to be a quick and reliable tool in detecting raised intracranial tension. This study aims to use bedside optic nerve sheath diameter (ONSD) measurements by ultrasonography and its correlation with clinical and radiological evidence of raised intracranial tension and the subsequent changes following medical intervention and lumbar puncture (LP) procedure. Materials and methods: A prospective observational study including 150 total participants from the emergency department of Bapuji Hospital, Davangerewas taken up, for a duration of six months from January 2022 to June 2022. Group A consisted of patients above the age of 18 years presenting with clinical features of raised intracranial tension - fever, headache, vomiting, seizures, altered sensorium evaluated using Glasgow coma scale and cerebrovascular accident. Group B, those patients who did not have any clinical signs of raised ICP, otherwise healthy subjects were taken as controls. Ultrasonographic measurements of the optic nerve sheath, 3mm behind the globe in supine position was done consecutively for 2 days using a 10 MHz linear array probe, this diameter was then compared to the ONSD in MRI/CT brain scans and correlated. Midline shift, edema, effacement of sulci and gyri with effaced ventricles on radiographic analysis suggested raised ICP. In 19 patients diagnostic lumbar puncture was performed as indicated. Prior to the procedurepharmacological measures to reduce edema was administered to the patients and subsequently US-ONSD was measured and compared to the same 30 minutes post the procedure. Appropriate statistical analysis was done and data interpreted. Results: There was a highly significant difference noted in the ONSD between the healthy subjects and patients presenting with raised ICP. Mean difference was 0.8307 mmwhichsuggested that US-ONSD was higher among patients when compared to healthy subjects. Also,thedifferencebetween clinical and radiological ONSD was-0.15 suggesting radiological ONSD to be higher than clinical ONSD but the variationwas small calculated using Hedges g. Pre and post lumbar puncturedifference in US-ONSD was found to be 0.22 mm. Amongst patients who underwent lumbar puncture 68% patients found reduction in symptoms which was resembled by the decrease in US-ONSD. Conclusion: Bedside measurement of US-ONSD is a useful tool to identify raised ICP. It has an advantage of being non-invasive and hence can be repeated multiple times and applied in many situations. Also changes in US-ONSD following pharmacological intervention and lumbar puncturebrings to light its reliability in identifying changes in ICP once the pressure is reduced.