Because the investigator's workplace and department have been changed, this study cannot be carried out.

Hydrocephalus is a disturbance of cerebrospinal fluid production, flow and absorption leading to intracranial hypertension. Assessment of the change in intracranial pressure after ventriculoperitoneal shunt surgery is important in guiding appropriate postoperative management. The optic nerve sheath diameter measured using ultrasonography has been verified as a non-invasive indicator of intracranial hypertension in various clinical studies. The investigators hypothesized that a change in optic nerve sheath diameter detected through ultrasonography could help ascertain a reduction in intracranial pressure following ventriculoperitoneal shunt surgery in adult patients without the risk of serious complications.

Inclusion Criteria:

• Adult patients (20-90 years of age, ASA physical status 3 or less) who are scheduled for elective ventriculoperitoneal shunt surgery with non-communicating hydrocephalus and communicating hydrocephalus except for normal-pressure hydrocephalus
• Non-communicating hydrocephalus is defined as a pattern of ventricular system or at the level of the fourth ventricle's outlets by lesions including tumor, giant aneurysm, or aqueductal stenosis.
• Communicating hydrocephalus is defined as paraventricular enlargement resulting from postoperative complication after cranial surgery, meningitis, subarachnoid or intracerebral hemorrhage.

Exclusion Criteria:

• Patients with previous history of shunt operation, ocular disease and ocular surgery
• Patients with anatomical or functional abnormality of optic nerve
• emergency patient

Patients who are scheduled for elective ventriculoperitoneal shunt surgery under general anesthesia