Study: More than 50% of patients may experience transient vision loss after trabeculectomy

The researchers also examined the ‘snuff-out’ phenomenon of unexplained severe vision loss after uncomplicated filtration surgery.

Brian A. Francis

The incidence of decreased vision after an uncomplicated trabeculectomy was found to be more than 50% in a retrospective review, but the majority of patients eventually recovered vision.

“The vision loss was temporary in 56.5% of eyes, which we felt was surprisingly high. We thought it would be around 30%,” lead author Brian A. Francis, MD, MS, an associate professor of ophthalmology at Doheny Eye Institute, said in an interview with Ocular Surgery News. The finding that most patients recover vision provides “more hope to patients who have some vision loss after surgery. In most cases, in fact, the vision comes back.”

Transient vision loss

The study, published in Archives of Ophthalmology, reviewed the medical records of 301 eyes of 262 patients who underwent trabeculectomy with mitomycin C at Doheny Eye Institute between 1999 and 2003. Follow-up was up to 24 months.

Another surprising finding of the study was how long it took vision to recover in the 170 eyes (56.5%) with transient vision loss.

“Typically, we would expect restoration of vision to occur within about 1 month,” Dr. Francis said. However, the average time to recovery was about 3 months. “And in some cases, it took 6 months or an entire year before the vision was normal again.”

The mean time to recovery was 88 days for mild or moderate transient vision loss, defined as a decrease in Snellen visual acuity of three to five lines, and 78 days for severe transient vision loss, defined as a decrease of more than five lines.

One patient recovered vision after 2 years. “We had kind of written him off as having permanent vision loss. But then at 2 years, the patient’s vision had recovered to baseline,” Dr. Francis said. “This was pretty impressive.”

‘Snuff-out’ phenomenon

Permanent vision loss occurred in 24 eyes (8%). No identifiable cause of vision loss was found in 10 eyes (3.3%) with permanent mild or moderate vision loss and six eyes (2%) with permanent severe vision loss.

The authors were inspired to undertake the study “by the myth, if you will, of the ‘snuff-out’ phenomenon, whereby patients with advanced glaucomatous optic nerve damage experience unexplained severe vision loss following uncomplicated filtration surgery,” Dr. Francis said. “Snuff-out is considered a myth because it is controversial whether it even exists or not and, if it does, how prevalent is the condition.”

The three significant risk factors for snuff-out identified by the authors were the presence of split fixation on a visual field test, the number of quadrants of split fixation (the greater the number, the higher the risk) and postoperative choroidal effusions.

“We found that having a choroidal effusion anytime after surgery, even after resolution, resulted in a higher risk for unexplained vision decrease,” Dr. Francis said.

The authors also evaluated the incidence of any vision loss after trabeculectomy and recovery of vision.

“This is the first study to look at both recovery of vision loss and the total incidence of vision loss,” Dr. Francis said.

“Try to manage the disease before it evolves to the advanced stage, so you can reduce the risk of operating on patients,” Dr. Francis said. “Counsel patients that if they have decreased vision, to be patient. The majority of time it will return to baseline.”

The authors may conduct a similar study on vision decrease with a different surgical procedure, such as an aqueous tube shunt for glaucoma. – by Bob Kronemyer

Reference:

• Francis BA, Hong B, Winarko J, Kawji S, Dustin L, Chopra V. Vision loss and recovery after trabeculectomy. Arch Ophthalmol. 2011;129(8):1011-1017.

• Brian A. Francis, MD, MS, can be reached at Doheny Eye Institute, 1450 San Pablo St., Suite 4804, Los Angeles, CA 90033; 323-442-6454; email: bfrancis@usc.edu.
• Disclosure: Dr. Francis has no relevant financial disclosures.