New devices assist in vision restoration

Pittsburgh-Sensory substitution devices (SSD) are in development as vision restoration technology for the blind, but a lack of accepted standards for screening users and evaluating their performance represents an important impediment to the ultimate clinical success of these platforms, said Amy Nau, OD.

In addition, it is possible to apply psychophysical assessments unrelated to the visual pathway using this investigational device.

As a vision device, this SSD has been in development for about 5 years. In its current iteration, this SSD uses a 400-electrode array to provide real-time interpretation of a video scene that is adequate for users to capture basic images.

"This device produces some functionality for people who are blind," said Dr. Nau, assistant professor, UPMC Eye Center, McGowan Institute for Regenerative Medicine, and director of Optometric Services and the Sensory Substitution Lab, University of Pittsburgh Medical Center, Pittsburgh.

"However, because the image resolution is not that good, more complex scenes are difficult to interpret with accuracy," Dr. Nau said. "Nevertheless, we do have some users able to enjoy activities such as playing pool, darts, or golf putting after sufficient training."

Computer-based tests developed for retinal implants have been shown to be applicable to the BrainPort for evaluating light perception and ability to detect location (BaLM), grating acuity (BaGA), and resolution acuity (FrACT). Results from these tests for predicting resolution acuity show that the device can produce spatial vision with an acuity level determined by the distance between the electrodes, according to Dr. Nau.

"Contrast sensitivity testing indicates that the subjects were not sensing shades of gray very well, and Vernier acuity testing did not work, but a denser array may improve contrast detection and allow subjects to perform a Vernier task," she added.

A video eye-tracking system (Eyelink 1000 desktop system, Inition) was used to record eye movements and found that users had reduced frequency and amplitude of nystagmus. Visual field assessment was ultimately possible using a tangent screen with modified targets and showed the average extent of the field was 56°, with the vertical field slightly less than the horizontal, 54° versus 58°.

"The results show the [device] allows users to perceive a good portion of their environment, and we consider the results promising," she added.