====== Postoperative visual loss ======

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 [[vasoconstrictor]]s 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]]

● [[hemodilution]] or overuse of [[crystalloid]] vs. colloid (blood) fluid replacement

● 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's 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