Background: Presentation of patients with altered sensorium to the emergency department is very common. Central nervous system (CNS) infections, cerebrovascular accidents and traumatic brain injury are common for such situation. Raised Intra cranial Pressure (ICP) is a dreaded complication of neurological disease and head injury, hydrocephalus, subarachnoid haemorrhage and intracranial haematoma that often leads to adverse outcomes either by reducing cerebral perfusion pressure (CPP) and causing cerebral ischemia or by compressing and causing herniation of the brain stem or other vital structures. Since there is paucity of literature, this study was undertaken to measure the optic nerve sheath diameter in patients presenting to the emergency department and correlation of optic nerve sheath diameter with raised intracranial pressure. Materials and Methods: A Comparative Analytical study of Optic Nerve Sheath Diameter in patients presented to Emergency Medicine Department was conducted. From an earlier study about measuring optic nerve sheath diameter using ultrasonography in increased intra cranial pressure, the sensitivity of Ultrasonography was 75% and specificity of 100%. All adult patients with clinical features suggestive of raised intracranial pressure brought to the Emergency Department in casualty, at SSG HOSPITAL, who underwent CT-brain. Results: History of trauma was present in 33.3% of the patients with raised intracranial pressure and 24.4% of the patients without raised intracranial pressure in this study. The history of fever was present in 10.4% of the patients with raised intracranial pressure and 14.6% of the patients without raised intracranial pressure. History of vomiting present in 61.5% of the patients with raised intracranial pressure and 62.5% of the patients without raised intracranial pressure. The history headache was present in 47.9% of the patients with raised intracranial pressure and 42.7% of the patients without raised intracranial pressure. The history of convulsion was present in 46.9% of the patients with raised intracranial pressure and 50.0% of the patients without raised intracranial pressure in this study. The history of unconsciousness was present in 55.2% of patients with raised intracranial pressure and 59.4% of the patients without raised intracranial pressure. This study had shown that, bradycardia was present in 52.1% of the patients with raised intracranial pressure and 34.4% of the patients without raised intracranial pressure. The elevated blood pressure was present in 59.4% of the patients with raised intracranial pressure and 52.1% of the patients without raised intracranial pressure in this study.