Staging of Surgical Procedures. The majority of spine surgery
patients who experience perioperative ION undergo prolonged
procedures with substantial blood loss while they are
positioned prone. Although the literature is insufficient to examine
the impact of surgical staging on reducing the frequency
of perioperative visual loss in spine surgery patients (Category D
evidence), an observational study indicates that, in 94% of ION
cases listed in the ASA Visual Loss Registry, anesthetic duration
exceeded 6 h9 (Category B2 evidence). A related retrospective
study reported an association between duration of anesthesia
and frequency of eye injury after a mix of nonocular surgeries43
(Category B2 evidence).