September 2008

 

OPHTHALMOLOGY NEWS

 

Visual loss related to nonocular surgery


by Vanessa Caceres EyeWorld Contributing Editor

 

 

Ischemic optic neuropathy and CRAO most common types of loss

Not all surgical-related visual complications occur due to problems after ocular surgery. A study published in the April issue of the American Journal of Ophthalmology found reports of peri-operative visual loss after nonocular surgeries ranging from 0.002% to 0.2%. The incidence may increase as the types of surgeries with which this problem is associated, such as spinal surgery, are performed more frequently, said study investigator Nancy J. Newman, M.D., professor of ophthalmology and neurology, Emory University, Atlanta.

“As technology advances and there are longer surgeries with the patient in the prone position, there will be an increase in this problem because of the increase in surgeries,” she said.

Other surgeries included in Dr. Newman’s literature review tracked peri-operative visual problems included cardiac and neck procedures as well as vascular and orthopedic cases.

Even though studies like Dr. Newman’s can track what kinds of visual loss occur, no one is certain which patients are at the highest risk for visual loss until it actually happens.

Types of loss

Anterior ischemic optic neuropathy (AION) was the most common type of visual loss associated with cardiac surgery patients, while posterior ischemic optic neuropathy (PION) was more common among patients with spine and neck surgery.

“The most common site of permanent injury to the visual pathways in the setting of general anesthesia for nonocular surgery include the optic nerves, and the most often presumed mechanism of injury in this location is ischemia,” Dr. Newman wrote. Patients with AION will present with acute manifest disk edema, while PION patients have a normal acute appearance via fundoscopy. In both types of ION, pupillary reactivity is abnormal.

The increase of ION associated with spinal surgery has become such a concern that the American Society of Anesthesiologists (ASA) established a registry in 1999 called the Postoperative Visual Loss (POVL) for voluntary, anonymous reporting of patients with visual loss within seven days after nonocular surgery (www.asaclosedclaims.org). A 2006 study in the journal Anesthesiology based on statistics in the registry reported that ION was associated with 83 of the 93 spinal surgery cases that the investigators had reviewed. The mean duration of anesthesia was 9.8 hours, estimated blood loss was 2.0 liters, and bilateral disease was seen in 55 patients. “Ischemic optic neuropathy cases had significantly higher anesthetic duration, blood loss, percentage of patients with Mayfield pins, and percentage of patients with bilateral disease compared with the remaining 10 cases of visual loss diagnosed with central retinal artery occlusion,” the study investigators wrote.

These patients often have very poor visual function, Dr. Newman wrote, citing one study that reported counting fingers visual acuity or worse in 76% of eyes with peri-operative PION and no light perception in 54%. Hand motions or worse final visual acuity remained in 55% of patients.

Central retinal artery occlusion (CRAO) is another common occurrence in patients with nonocular surgery-related visual loss. “Central retinal artery occlusion can result from systemic or local arterial embolism, the likely cause when this complication occurs in the setting of cardiac and other vascular surgeries,” Dr. Newman wrote.

The CRAO that occurs is usually unilateral and exhibits other signs, such as external compression of the periorbital tissues or the globe or both.

Dr. Newman’s review also found visual loss from injury to the retrochiasmal visual pathways and the anterior segment, but these were not as common or as severe as ION and CRAO.

Causes

Although there are theories about why visual loss associated with peri-operative ION occurs, no one is quite sure.

Risk factors “include hypotension, relative hypotension, anemia, blood loss, hypoxia, hemodilution, hypovolemia infusion of large amounts of crystalloid, use of vasoconstricting agents, head position either above or below the heart, elevated venous pressure, elevated intraocular pressure, ocular globe compression, and an individual suspectibility (perhaps anatomically or physiologically related to the blood supply to or from the optic nerves). All of these factors could theoretically play a role in the development of ION, with the exception of ocular globe compression and elevated intraocular pressure,” Dr. Newman wrote. Those two may factor into the development of CRAO, she said.

Still, it’s difficult to pinpoint the exact cause of peri-operative ION because the cause may vary by procedure, and the risk factors may be different in each patient, Dr. Newman said.

That said, a task force formed in 2005 by the ASA published a Practice Advisory to assist with decision making related to peri-operative visual loss associated with spinal surgery. Their report classifies patients at high risk for peri-operative visual loss as ones undergoing spinal procedures and receiving general anesthesia who will have prolonged surgery, substantial blood loss, or both factors. They recommend that surgeons consider informing these patients of the small but unpredictable risk of peri-operative visual loss. These patients should be positioned with their heads at level with or higher than the heart, if possible.

Ophthalmologist’s role

Although ophthalmologists may not be on the frontline when seeing these patients and may not face the medico-legal risks that the primary surgeon faces if this visual loss occurs, they should still be aware of this problem, Dr. Newman said. “Once or twice in their career, it will come up,” she said.

“This goes to show that not all causes of visual loss are apparent,” said David R. Hardten, M.D., adjunct associate professor of ophthalmology, University of Minnesota, Minneapolis.

The ASA Practice Advisory recommends that if visual loss is seen once the patient is alert (such as in the recovery room), an urgent ophthalmologic consultation should be obtained. “If an obvious ocular cause such as globe injury or central retinal artery occlusion is not apparent, then urgent neuroimaging should be obtained, preferably MRI with gadolinium and stroke protocol techniques, to assess for intracranial pathology such as pituitary apoplexy or occipital infarction,” Dr. Newman wrote. “If imaging is unrevealing, the likely cause of visual loss is ION.”

Although the visual loss is usually so devastating it will be detected in the hospital, it’s not unheard of that an ophthalmologist might see these patients for an office visit, Dr. Newman said. In that setting, ophthalmologists need to carefully document what they find but be careful not to speak too much about causation, unless they are absolutely certain of the cause of visual loss as it relates to the patient’s surgery.

Performing a visual field test also may be helpful to detect problems not obvious during other parts of the exam, Dr. Hardten said.

Editors’ note: Drs. Newman and Hardten have no financial interests related to their comments.

Contact Information

Hardten: 612-813-3632, drhardten@mneye.com

Newman: ophtnjn@emory.edu

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