1. ischemic optic neuropathy: The most common cause of the very uncommon postoperative visual loss. Often bilateral. Usually associated with significant blood loss (median: 2 L), and/or prolonged operative time ( ≥ 6 hrs ). All cases had anesthetic time > 5 hrs or blood loss > 1 L. Blood loss can cause hypotension (may cause release of endogenous vasoconstrictors in addition to reduced blood flow due to low hemodynamic pressure) and increased platelet aggregation. Is not due to direct pressure on the globe in most cases, and can occur at any age and even in otherwise healthy patients. No association with age, HTN,atherosclerosis, smoking or DM.
The blindness can be extensive and is often permanent. Prevention is critical since there is no known effective treatment.
a) posterior ischemic optic neuropathy (PION): may follow surgery (surgical PION).
Risk factors as above, plus:
● Surgery in the prone position (can cause periorbital edema, and rarely, direct pressure on the orbit)
● lack of tight glycemic control
● use of Trendelenburg position
● prolonged hypotension
● cellular hypoxia
● decreased renal perfusion
b) 6 independent risk factors for POVL
● male gender:odds ratio(OR)=2.53
● obesity: by clinical assessment or BMI≥30 OR=2.83
● use of Wilson frame: OR=4.30
● length of anesthesia: OR=1.39 per hour
● EBL: OR=1.34 per Liter
● use of colloid as a percentage of nonblood replacement: less certain (small di erence). OR= 0.67 per 5% colloid
c) anterior ischemic optic neuropathy (AION): divided into arteritic (as with GCA) and nonarter- itic (common with DM)
2. central retinal artery occlusion
3. cortical blindness: from occipital lobe infarction possibly due to embolis