Design
Review of all cases of ION that developed within 2 weeks of spine surgery at two academic institutions from 1990 to 1992, and a review of adequately reported cases of ION after other nonophthalmic procedures.

Results
Four new cases are reported in patients who ranged in age from 41 to 65 years. All four had undergone uneventful but prolonged (8 to 9 hours) spine surgery, during which blood pressure was deliberately maintained between 85 and 100 mm Hg systolic and 45 to 65 mm Hg diastolic to reduce bleeding. Hemoglobin values fell 30 to 78 g/L during surgery. Arteriosclerotic risk factors, including systemic hypertension, diabetes, coronary artery disease, and smoking, were present in three cases. There was no evidence of orbital soft-tissue injury, retinal artery occlusion, or other neurologic deficits. The combination of hypotension and anemia has been noted in most of the 30 previously well-documented cases of ION after other nonophthalmic procedures.

Conclusions
Multilevel lumbar laminectomy should be added to the list of procedures that may produce ION as an isolated complication. Deliberate hypotension maintained for long operative periods in patients with arteriosclerotic risk factors may be the cause.