A portable device that captures high-resolution images inside the eye could be an effective way to monitor eye health, especially for people in developing countries.
The device can take finely detailed images of the macula, the spot in the center of the eye where vision is sharpest, without artificially dilating the pupil. Those images can then be sent by cellphone to ophthalmologists who can make a diagnosis remotely.
The eye is the body’s only portal that allows direct, noninvasive imaging of internal tissue like blood vessels. Generally, doctors have to dilate a patient’s eyes—an uncomfortable, time-consuming process—before an exam that often involves bulky, expensive equipment.
In creating the new device, the challenge was to produce something portable that provides high-quality images of the macula without dilation.
“Whatever you look directly at you see in very high resolution, while your peripheral vision is blurry,” says Ashok Veeraraghavan, assistant professor of electrical and computer engineering at Rice University. “The region of the retina that provides you with this high resolution is the macula. And degradation of the macula immediately affects your eyesight.”
“When we talk to physicians about this project, the first question they always ask is, ‘Can you image the macula?'” says research engineer Adam Samaniego. “So that’s where we decided to focus our efforts.”
How it works
The new device, called mobileVision, looks and works something like a reverse microscope. A patient looks into the eyepiece and sees a large dark red disk. When the system is shifted around freely, the appearance of the disk changes dramatically—appearing brightest and most uniform when perfectly aligned with the patient’s eye.
When this happens, the patient hits a button that moves the target out of the way and allows the camera to see into the eye, with help from a battery-powered light source.
“That dark target induces pupil dilation naturally,” Samaniego says. “When you present the eye with a stimulus that isn’t throwing a lot of photons at it, the eye dilates to collect more light and have a better look.” When the patient can clearly see the disk, the pupil is dilated and the system is aligned.
Once the retina is illuminated, “We have a window of only a few hundred milliseconds to snap as many frames as we can before the pupil constricts again.”
At that point, the patient’s job is done. In an ideal situation, a mobile clinic anywhere in the world could use multiple mobileVision systems to gather data from many patients very quickly.
“There might be one individual who’s telling a number of people how to do different tests with different devices,” Samaniego says.
In the lab, mobileVision is connected to a small camera and tied to a computer. But in the field, a cellphone would capture video and break it down into a series of still images that can be analyzed and enhanced through a computational technique known as “lucky imaging.”
“This technique was invented for astronomers who image stars from Earth and have to correct for the effects of atmospheric turbulence that cause a loss in resolution,” Veeraraghavan says.
“The naïve thing to do is take hundreds of images and use the best one. You would feel lucky if you found something that looked good,” he says.
Instead, the new algorithm takes a sampling of the many images captured before the pupil closes and fuses them to enhance the features.
The researchers presented the first comprehensive results of their work at the Wireless Health 2014 conference in October.
Source: Rice University