Experts Debate Usefulness of Vision Restoration Therapy

November 1, 2007

Vision Restoration Therapy (VRT) is an FDA-cleared device for treatment of visual field defects caused by stroke or traumatic brain injury. The therapy works by stimulating the brain to form new connections, according to NovaVision, the device's manufacturer. But critics maintain that VRT is nothing more than a pricey way to promote saccadic eye movement.

Vision Restoration Therapy (VRT) is an FDA-cleared device for treatment of visual field defects caused by stroke or traumatic brain injury. The therapy works by stimulating the brain to form new connections, according to NovaVision, the device's manufacturer. But critics maintain that VRT is nothing more than a pricey way to promote saccadic eye movement.

Jose G. Romano, MD, associate professor of neurology at the University of Miami, who serves on Nova- Vision's Scientific and Medical Board of Advisors, said that VRT has been shown to increase the visual field by about 5 degrees. "The improvements are likely due to cortical reorganization," he added.

But Victoria S. Pelak, MD, associate professor of neurology and ophthalmology at the University of Colorado Health Sciences Center in Aurora, who wrote a recent review on treating visual field defects,1 said that there are a "lot of holes" in both the results and the purported mechanism behind them. For example, most studies are able to detect positive results only when using a measure of the visual field developed by the inventors of VRT. Even if the therapy does work, she said, it is likely that the benefit derives from adaptive strategies, not neuroplasticity.

"I think that VRT very likely does train a person to increase attention to a blind spot," Pelak said. "But the way the company has gone about marketing it, claiming it does more than it really can, is something that has been bothersome to a lot of people."

PERSONALIZED TREATMENT PLAN

VRT is available at about 50 centers in the United States; about 1000 persons have been treated at these centers so far. The treatment is for persons with visual field defects, such as homonymous hemianopia. Patients with ocular or cerebral disease or significant cognitive defects are not candidates for the therapy.

After screening in a doctor's office, eligible patients receive a personalized laptop computer device for home use. Therapy involves viewing a monitor that flashes light stimuli in the area of residual vision between the scotoma and the intact visual field. The user is instructed to press a button each time these stimuli appear.

The device keeps the user's eyes centered by presenting a fixation target that requires the user to press a button each time the target changes color. "If you move your eyes, it's hard to detect the change," said Romano.

Therapy involves two 30-minute treatment sessions a day, 6 days a week, for 6 months. The device re-maps the user's vision each month, and the results are sent to NovaVision for analysis and adjustment of the treatment plan.

"The new plan accounts for shifting of the border between sight and blindness," said Romano. "Or, if there's no improvement, there might be a need for a new treatment paradigm," he said. Adjustments may include changing the pattern of stimuli presentation, increasing or decreasing the intensity of the stimuli, or changing the color or form of the stimuli.

SACCADES VERSUS NEUROPLASTICITY

In a 161-person study that Romano presented at the American Academy of Neurology meeting in Boston last May, 76% of patients with homonymous visual field defects benefited from the therapy.2 The average increase in visual field was about 5 degrees, which he said was consistent with previous studies. For example, in a study by Kasten and colleagues,3 VRT expanded the visual field by an average of 4.9 to 5.8 degrees.

"Five degrees may not sound like much, but it can be very significant," Romano said. He pointed out that reading takes place in the central 5 degrees of vision, so that losing or gaining just half of that can have a sizable effect on such daily activities besides reading as using a computer or watching television.

Although the exact mechanism behind the improvement is unclear, Romano said that some type of neuroplasticity is involved. "It could be the reconnection of surviving neurons, but more likely it is either increased attention to the border between the seeing and blind fields or the activation of previously underused pathways to bypass damaged areas in the brain," he suggested.

Is is unlikely that saccades could explain the vision improvement, Romano said, citing a recent study by Kasten and colleagues4 that accounted for eye movement. In this study, the researchers used a 2D Eye Tracker (Chronos Vision) to monitor eye position perimetry testing. The researchers found that eyes remain within 2 degrees of fixation 98.9% of the time. "I thought this paper was convincing," said Romano.

Pelak, however, dismissed the idea that neuroplasticity could explain the vision improvements. "It probably has more to do with the person's attention-being able to make very, very small movements of their eye-to detect these areas," she said. She pointed out that just 2 degrees of movement could account for the improvement with VRT.

Romano said that if the eye movements were within 2 degrees, they would be too small to explain the 5 degree shift in the visual field defect. But Pelak pointed out that the articles in peer-reviewed journals do not support a 5-degree shift: "Five degrees is constantly claimed, but it is nearly always 2 degrees or less if any improvement is found at all with threshold testing."

Another argument against neuroplasticity, Pelak said, is the fact that vision improvements occur only in the central visual field. "They stimulate other areas beyond the central 5-degree field if the person's vision loss begins at 6 degrees away, so why don't these patients show improvement?" she asked. She added that if neuroplasticity were occurring, it should occur in the peripheral areas as well as in the central ones. "Why isn't there something out 15 degrees?" she asked.

She also took exception to Romano's statement that early data from Julkunen and colleagues5 of imaging studies with positron emission tomography and functional MRI support the concept of neuroplasticity because they have shown functional changes in the brain after visual stimulation.

"That's a huge can of worms [for NovaVision] because those types of imaging studies have not been proved to represent neuronal plasticity," said Pelak. "These could be the normal changes that take place when your brain gets trained to do something."

SUPRATHRESHOLD TESTING

Pelak also objected to the use of high-resolution perimetry (HRP)-which was developed by Sabel and Kasten, the researchers who developed VRT-to measure improvements. Unlike a standard threshold visual field test like Tübinger automatic perimetry (TAP), which measures the ability to see gradually brighter stimuli, HRP is a suprathreshold test that presents only very bright stimuli. This type of test may allow peripheral retinal loci to detect light. "There is no analogous visual field machine that's used in the practice of ophthalmology or neuro-ophthalmology," she said.

In addition, Pelak pointed out the inherent credibility problem in having the same researchers design both a product and the device used to evaluate it. In fact, the evidence suggests that standard measures are unable to detect a benefit with VRT.

For example, in a study of 19 patients with post- chiasmal injury, HRP detected improvements in the average number of correct responses and the visual field border position, whereas TAP detected no improvements.3 In a companion study of 19 patients with optic nerve injury, the visual field expanded by 5.8 degrees when measured by HRP but only 2.1 degrees when measured by TAP.3

In addition, 3 studies that looked at the same set of 16 or 17 patients revealed different results depending on whether HRP, scanning laser ophthalmoscopy (SLO), or TAP was used. Sabel and colleagues6 found that the visual field increased by an average of 1.73 degrees and that the average number of correct responses had increased from 63% to 69% when measured by HRP. When Schreiber and colleagues7 published data on the same patients, however, they reported that only 2 patients experienced more than 2 degrees of enlargement of the visual field using TAP-and the improvements were in just 1 eye. Reinhard and colleagues,8 using SLO, also found that VRT was not effective: the visual field border had shifted in just 1 of 34 eyes after 6 months of treatment.

Romano countered that the Reinhard study is just one of many and that SLO testing is not a good measure of improvement in patients with visual field defects. "The task required to complete the SLO is too difficult for these persons and, therefore, absence of improvement in SLO does not negate the ability to respond to less difficult tasks presented in other types of perimetries," he said.

FUNCTION

Pelak also said that VRT has never been shown to improve function. "The jury is still out on whether it causes functional improvement. The company says that it does, but studies that are more independent have not shown those types of results," she said.

Reinhard and colleagues8 did find a slight increase in reading speed with VRT. Romano also pointed to a retrospective analysis by Mueller and colleagues9 in which 88% of 69 patients receiving VRT reported subjective improvements in activities of daily living, specifically "carrying out hobbies" and "general improvement in vision." But Pelak pointed out that the patients did not improve on most of the subjective measures in this study and that the improvements that did occur failed to correspond with the changes on HRP-an admission that the study authors make themselves.

COSTLY THERAPY

Vision restoration therapy typically costs about $6000 and is not covered by insurance. Pelak said that insurers are justified in denying coverage for the treatment because it has not been proved to work. The product was cleared by the FDA on the basis of it being "functionally equivalent" to 2 other vision devices on the market. The FDA has never reviewed data on VRT's effectiveness. Romano, however, said that $33 a day is right in line with other rehabilitative interventions and that NovaVision is working with Medicare to obtain reimbursement.

INCREASED RECOGNITION OF VISUAL DEFECTS

There is one point on which the 2 researchers agree: that the introduction of VRT has increased awareness of visual field defects.

"It's nice to get it out there that there are treatments for this," said Pelak. She said that physical and occupational therapy can help persons learn to compensate for their deficits and that some people find special prism glasses to be helpful. "But the treatment that seems to have the most potential is eye movement training," she said. She pointed to a visual rehabilitation strategy designed by Spitzyna and colleagues10 that involves 400 minutes of therapy over 4 weeks on a free Web site (www.ucl.ac.uk/mediares/mm/mm-projects/neurology/read_right). She added that further research is needed to determine whether such training can improve persons' lives.

References:

REFERENCES


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