Postoperative delirium is a sudden and reversible disturbance of mental function, occurring after surgery, characterized by confusion, inattention, and fluctuating mental status, which can manifest as agitation or lethargy. It is a common post-operative complication, especially in older adults, and is associated with longer hospital stays and worse recovery outcomes. Validated delirium screening tools such as the Intensive Care Delirium Screening Checklist (ICDSC) and the Richmond Agitation and Sedation Scale (RASS) are widely used tools to assess delirium. However, the sensitivity of these screening tools can be variable when used in real-world practice and may miss early cases of delirium. The optic nerve sheath is a protective sheath that encloses part of the optic nerve that is located at the back of the eye. Measurement of the optic nerve sheath diameter is usually done using ultrasound to detect increased cranial pressure. Previous studies that have been conducted have shown that increased ONSD may be associated with occurrence of postoperative delirium. The purpose of this study is to determine if there is an association between optic nerve sheath diameter (ONSD) and the occurrence of delirium after surgery. This study will be conducted at the London Health Sciences Centre and will include 300 patients.
A d u l t s ≥ 1 8 y e a r s .
Scheduled for cardiac surgery requiring cardiopulmonary bypass (CPB) (e.g., Coronary artery bypass graft (CABG), valve, combined procedures, aortic surgery).
Anticipated postoperative admission to the Cardiac ICU with expected stay >48 hours.
Preoperative ability to undergo ocular ultrasound examination (closed-eyelid scanning).
Known or suspected open-globe injury, penetrating ocular trauma, or intraocular foreign body.
Recent ocular surgery or intravitreal intervention within the past 6 weeks (if surgeon advises against periocular pressure).
Ocular conditions that invalidate ONSD measurement (e.g., severe proptosis, advanced optic neuropathies, orbital tumors) or obstruct ultrasound window (extensive periocular dressings, severe periorbital edema).
Known intracranial pathology expected to significantly alter baseline ONSD (e.g., large mass lesion with midline shift, obstructive hydrocephalus) or presence of external ventricular drain at baseline.