Ultrasonographic Optic Nerve Sheath Diameter in Postdural Puncture Headache Diagnosis

Inclusion Criteria: * Age between 18 and 65 years * ASA physical status I or II * Scheduled for total knee arthroplasty under spinal anesthesia * Successful spinal anesthesia with a single attempt using a 27G Quincke spinal needle * Provided informed consent to participate in the study Exclusion Criteria: * History of neurological or central nervous system disorders (e.g., cerebrovascular disease, intracranial hemorrhage, brain tumor) * Ophthalmological disorders * Hypertension * Hepatic encephalopathy * Renal failure * Pregnancy * History of chronic headaches or migraine * Obesity (BMI \> 35 kg/m²) * Alcohol or substance abuse * Psychiatric disorders * Local infection at the injection site * Allergy to local anesthetics * Bleeding diathesis * Requirement for sedation during the procedure * Inability to cooperate postoperatively (e.g., mental retardation, language deficits) * Inability to obtain reliable ONSD measurements