Chapter 96

### INTRODUCTION

Visual loss after anesthesia and surgery is a rare and devastating complication, with the most frequent cases occurring after spinal fusion and cardiac surgery. It should be considered in any patient who complains of visual loss during the first week after surgery. The most frequently reported cause of postoperative visual loss (POVL) is ischemic optic neuropathy. Ischemic optic neuropathy has also been reported in patients undergoing radical neck operations and robotic-assisted prostatectomy in steep Trendelenburg positioning. Other less common cases of POVL include retinal artery occlusion, cortical blindness, and ophthalmic vein obstruction.

### ISCHEMIC OPTIC NEUROPATHY

The optic nerve can be divided into an anterior and posterior segment depending on blood supply. The central retinal artery and small branches of the ciliary artery supply the anterior portion of the optic nerve, while the small branches of the ophthalmic and central retinal arteries supply the posterior portion of the optic nerve. Blood flow to the posterior segment of the optic nerve is less than that of the anterior segment and as such, ischemic events to the segments have different risk factors and physical findings.

#### Anterior Ischemic Optic Neuropathy

The visual loss due to anterior ischemic optic neuropathy (AION) is due to infarction of the watershed perfusion zones between the small branches of the short posterior ciliary arteries. Visual loss is usually painless and ranges from monocular visual deficits to complete blindness. Optic disc swelling and hemorrhage may be early signs of pathology.

Anterior ION is attributed to decreased oxygen delivery to the optic disk associated with hypotension and/or anemia. This type of visual loss has been associated with cardiac surgery, hemorrhagic hypotension, anemia, head and neck surgery, cardiac arrest, and hemodialysis. There have been reports of AION occurring spontaneously. Another form of AION, arteritic anterior ION, occurs due to inflammation and thrombosis of the short posterior ciliary arteries. The diagnosis is confirmed by temporal artery biopsy showing giant cell arteritis. Treatment includes high dose steroids.

#### Posterior Ischemic Optic Neuropathy

Posterior ischemic optic neuropathy (PION) is the more commonly reported cause of ischemic optic neuropathy (ION) in the perioperative period and is most commonly associated with prone posterior spinal fusion, with an estimated incidence of 0.017%-0.1%. Posterior ION has also been reported to occur after robotic procedures where the patient is in steep head down position for prolonged periods of time. Posterior ION presents with acute loss of vision and visual field defects similar to AION. It is caused by decreased oxygen delivery to the posterior portion of the optic nerve between the optic nerve and the point of entry of the central retinal artery. Initial ophthalmologic examination may not reveal any findings, but mild disc edema may be present after a few days.

Literature reviews demonstrate that most ION patients, after prone spine surgery, are relatively healthy ...

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