Postoperative Visual Loss

Introduction

Postoperative visual loss (POVL) after nonocular surgery is an uncommon but devastating complication. POVL is most common after cardiac surgery followed by prone spine and head and neck procedures, with a national incidence ranging from 0.03 to 0.28% in these higher risk surgeries. Specific institutions may see lower or higher rates, which may be related to the types of procedures performed, the patient population, or specific practice patterns. The most common diagnoses associated with POVL are central retinal artery occlusion (CRAO), ischemic optic neuropathy (ION) [anterior ION (AION) and posterior ION (PION)], and cortical blindness (also known as cerebral visual loss). This chapter will discuss the major POVL diagnoses including the predisposing or associated factors and procedures, presentation, evaluation, and management.

Central Retinal Artery Occlusion

CRAO occurs as the result of decreased blood supply to the retina. The mechanism of decreased blood flow can be secondary to emboli or external pressure on the eye. In the perioperative period, the usual cause is from improper head positioning and direct pressure on the eye. Pressure on the eye leads to increased intraocular pressure that compromises flow in the central retinal artery, the major vascular supply to the retina, leading to retinal ischemia. Some of the first reported cases of POVL were related to CRAO and started appearing in the literature around 1950. All these early reports were thought to be caused by direct pressure on the eye from a face mask and attachments or from a horseshoe headrest while in the prone position, and possibly exacerbated by hypotension. These findings were even replicated in animal models by decreasing blood volume and blood pressure while applying direct pressure on the eye while under general anesthesia.

CRAO almost always presents as unilateral visual loss upon awakening from anesthesia. Patients can have little or no light perception and an afferent pupillary defect with slowed or absent pupillary light reflex. There can also be signs of trauma to or around the affected eye including periorbital edema, ptosis, proptosis, corneal abrasion, ecchymosis, and paralysis of extraocular eye muscles. Fundoscopic examination reveals a cherry-red spot in the macular region and diffuse retinal ischemia. Prevention of CRAO is key, as prognosis is poor and treatment options such as hyperbaric oxygen therapy, inhaled 5% carbon dioxide in oxygen, and directed intra-arterial thrombolysis have inconsistent results and are frequently not possible in the postoperative period.

Every attempt should be made during positioning to ensure that the head is in the proper position and that there is no pressure on the eyes. Head movement can occur intraoperatively, and frequent eye checks should be done to confirm that the eyes remain free of pressure throughout the entire procedure. Horseshoe headrests have been associated with numerous case reports and case series of CRAO thought related to the narrow margin of safety as the firm portion of the headrest comes very close to the eyes. However, sporadic case reports of CRAO have also been associated with newer headrests, thus highlighting the importance of frequent eye checks. Although well-intentioned, the use of eye goggles may actually increase the risk of pressure on the eyes in the prone position because of the narrow margin of clearance around the eye, making it necessary to avoid two obstacles, instead of one, while positioning and throughout the case.