Blindness after any surgery is a possibility. There is only one artery that supplies the eye and with the patient face down, the eye is suspended. If there is pressure on the eye, trauma to this region or some very rare conditions where the artery is fragile and weak, loss of vision can occur.
I have seen this once in thirty years in a patient who had a major thoracic spine dislocation with paralysis. We took him to the operating room and repaired his thoracic spine. The surgery took 5 1/2 hours. Remarkably, he fully recovered from his paralysis but was left with partial visual loss.
ION (ischemic optic neuropathy) is very rare and precautions can be taken to reduce the potential, but the risk is there, especially with long cases (even open heart and other surgeries).
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.