Diseases such as glaucoma and retinitis pigmentosa progressively
destroy eye tissue, causing patients to lose peripheral vision. As a result, they
have tunnel vision. Patients who have tunnel vision usually use a long cane to avoid
stumbling over obstacles. Devices that offer a minified image of a patient’s
field of view have been developed, but they cause a significant loss of resolution
and a change in perceived visual direction. Therefore, they usually are rejected
by the patient.
Toward the creation of a better device, Dr. Eli
Peli and colleagues at Schepens Eye Research Institute, a Harvard Medical School
affiliate in Boston, are developing a video system with the help of MicroOptical
Corp. of Westwood, Mass. The video system continuously displays images of the periphery
of a patient’s environment onto a pair of spectacles. A patient can then use
his normal central vision to see through the glasses while viewing the displayed
edges, a principle that Peli calls “spatial vision multiplexing.” He
believes that a device based on that principle would not reduce resolution or disorient
patients because they can still use their central vision to peer through the display.
On these glasses are a tiny camera
that captures ambient images and a miniature computer that processes them into information
that contains only the edges of the environment. This information is transmitted
to an LCD element in the lens of the glasses, which displays images of the edges,
enabling patients with tunnel vision to peer at the broadcasted images and to use
their natural central vision to see through the glasses.
The device consists of off-the-shelf
parts, including a tiny image processor from DigiVision and a miniature Sony camera
that is mounted on the glasses. Working according to National Television System
Committee standards, the camera captures video of the patient’s environment.
The computer processes this information, so that only the edges of the environment
are relayed to the display. Using technology developed by MicroOptical, an internal
LCD element displays images of the edges at a resolution of 320 x 240 pixels. The
glasses update those images 30 times per second.
To test the device in a search task,
the investigators projected letters framed in circles or triangles at a random position
on a screen for 12 subjects with tunnel vision to identify. These letters initially
appeared in the patients’ blind area. When they found and recognized the target,
they clicked a mouse button and identified the letter verbally.
The head-mounted display significantly
improved the directness of the search and reduced the search time by 22 percent
for patients with a visual field between 10° and 15°. Visual acuity was
not reduced, so the researchers concluded that the resolution was not compromised.
Recently, the scientists tested how
the device might perform in a collision-avoidance task. In this test, patients walked
on a treadmill while viewing a virtual-reality shopping mall. Images of Peli in
a ski suit periodically popped up in the patients’ peripheral vision area,
testing their ability to detect the obstacle and determine the possibility of collision.
Eventually, the investigators want
to test the device outside. Peli said that he might employ orientation and mobility
trainers of the blind to evaluate the performance of subjects when they are wearing
the glasses outdoors. Because these instructors are already certified to protect
the blind and evaluate their performance, the need to train researchers and to develop
a method of evaluation would be eliminated.
Before placing the spectacles on the
market, Peli would like to further improve them. The original device was connected
to a shoebox-size controller that the patient had to carry, but the researchers
have since reduced the controller size to that of a cigarette pack. Peli said that
the device may be ready in five years and may cost $1000. The investigators also
have developed a low-light version of the glasses that employs an infrared camera.
Investigative Ophthalmology &
Visual Science, September 2006, pp. 4152-4159.
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