Anesthesiology APPLIED Exam › Neuroanesthesia and neuromuscular

Postoperative visual loss and prone positioning

Neuroanesthesia and neuromuscular·~4 min read· Physician-reviewed✓ Sourced · 2

Stem

A 58-year-old man, 118 kg with a BMI of 38, hypertensive and a smoker, is scheduled for a prone L2–S1 posterior instrumented fusion. The surgeon expects seven hours and 2 liters of blood loss and has asked for a Wilson frame. His hemoglobin is 13.2 g/dL and his blood pressure is 148/88 on lisinopril and amlodipine.

Question

What do you tell him about his risk of visual loss, and how will you manage the case to reduce it?

Ideal answer

HeadlineHe is high risk for ischemic optic neuropathy: prone, long and bloody, and male and obese on top.¹^,2 I tell him before surgery, then protect optic nerve perfusion.

Tell him plainly, and document it. Prolonged prone spine surgery with major blood loss carries a small but real risk of permanent visual loss; his sex and weight add to it.¹
Ask about shortening, staging, or a flat frame. The Wilson frame was an independent risk factor.¹^,2
Arterial line; pressure near his hypertensive baseline. No deliberate hypotension unless the surgeon and I agree it is essential.¹
Head level with or above the heart, neck neutral. Foam headrest or pins with no pressure on the globes, eyes checked regularly.¹
Periodic hemoglobin, appropriate transfusion, colloid with crystalloid. A lower colloid proportion was associated with optic neuropathy.¹^,2

Watch for: his vision in recovery, as soon as he is alert.¹

Breaking down the answer

Know the two lesions — ischemic optic neuropathy dominates, not pressure on the eye: in the ASA registry, 83 of 93 cases were ION and 10 were central retinal artery occlusion.² CRAO comes from external pressure and is typically unilateral; ION was bilateral in 55%.²
Six independent risk factors — male sex, obesity, Wilson frame, longer anesthesia, greater blood loss and a lower colloid percentage of non-blood fluid.² Naming them shows command of the evidence.
It is not just hypotension and anemia — those were not consistently present in registry ION cases, and two-thirds of patients were ASA 1–2.² Duration and venous congestion matter.
Inform, do not frighten — the advisory says to inform high-risk patients, case by case for others, and staged procedures may be used case by case for high-risk patients.¹ That fits the communication attribute examiners grade.

Follow-up question

In the PACU he says he cannot see out of either eye. His pupils react sluggishly, and he has no light perception on the left. His hemoglobin is 8.1 g/dL and his pressure is 102/60. What do you do?

Follow-up answer

HeadlinePerioperative visual loss, most likely bilateral ischemic optic neuropathy; I tell him what I see, call the surgeon and urgent ophthalmology.¹

While waiting, I optimize what I can: pressure back toward his baseline, transfusion to correct the anemia, oxygen to maintain arterial oxygenation, and head-up.¹ I consider CT or MRI to exclude an intracranial cause.¹ I tell him honestly there is no proven treatment for this condition,² that we are doing what may help, and that I stay involved; I document the exam and timeline and report it to the registry.

Pitfalls that cost points

Assuming that keeping pressure off the eyes prevents visual loss; it prevents CRAO, not ION.
Waiting until the next morning to test vision or call ophthalmology.
Promising a treatment that does not exist.²

Rapid-fire

Q: How common is ION after spine surgery? A: National data show about 0.017%, with smaller studies reporting up to 0.1%.²

Q: What does CRAO look like on fundoscopy? A: Retinal whitening, a cherry-red macula and attenuated arteries.²

Q: Has the incidence changed? A: It fell about 2.7-fold from 1998 to 2012.²

Q: Which other procedure is a classic setting for perioperative visual loss? A: Cardiac surgery.²

Q: Who should check the eyes during the case? A: I do, periodically, and after any repositioning.¹

Numbers to know

Item	Value
ION after spine surgery	~0.017% (national); up to 0.1%²
ASA POVL registry	93 spine cases: 83 ION, 10 CRAO²
ION bilateral	55%²
Independent risk factors	6²
Decline 1998–2012	~2.7-fold²

Sources

1.Practice Advisory for Perioperative Visual Loss Associated with Spine Surgery 2019 · ASA (Anesthesiology), 2019 · pmc.ncbi.nlm.nih.govUpdated by the ASA Task Force with NANOS and SNACC; an advisory, not a standard or guideline.
2.Postoperative Visual Loss (POVL) · APSF · apsf.orgIncidence (Shen 2009; Stevens 1997), ASA POVL Registry (Lee 2006), POVL Study Group risk factors (2012), Rubin 2016 trend.

Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.