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Wave-front sensor targets preschool vision

Wave-front sensor targets preschool vision

Skaneateles Falls, NY -It's appalling to consider that 1.2 million children in the U.S. have lost vision, simply because there's no technique to screen them effectively. The problem is that eye charts, vision testers, photo screeners, and most auto refractors aren't designed with young children in mind-the 3-to- 4 year olds who may lack the attention span to cooperate effectively, or be intimidated by the close proximity of a strange device. That's why a team of engineers at Welch Allyn developed the SureSight(TM), a portable and easy-to-use vision screener specifically designed for children that provides automatic, objective tests without the need for patient contact, responses, or even interpretation by the tester. The handheld vision screener projects a 2-mm beam of IR (infrared) light into the patient's eye from a 14-inch distance. Within a few seconds, the patient's optical characteristics appear on the built-in LCD display, which the tester can beam via IR link to a portable printer, or download via RS-232 directly into electronic medical records. SureSight is based on Hartmann Shack wave-front sensing technology that was previously used to correct the Hubble telescope, and to view individual rods and cones on the back of human eyes. "The technology has never been used in a commercialized product, or for this purpose," explains electronics engineer Corinn Fahrenkrug. "So we had to develop a feasibility unit, which turned out to be about the size of a desk." Its 3.5-ft long optical path requires seven circuit boards for operation.

Shrinking an optical bench unit the size of a desk to roughly the dimensions of a camcorder was no easy task, according to Fahrenkrug. The key was sculpting the Hartmann Shack sensor's optical response. "Rather than designing the sensor's performance across all refractive ranges," Fahrenkrug explains, "we reduced the required envelope by optimizing it only for particular ranges that allowed us to measure the refractive aberrations in our target age groups."


From an illumination source, light passes through a beam splitter onto the patient's retina. The retina reflects light back into the device, where the beam travels through a series of mirrors and into a microlens array, creating an image, which is sent to a CCD camera. The spot pattern of light formed is translated into sphere, cylinder and axis.

At a mere 2 lbs, the portable unit must stand up to significant wear and tear beyond that of a laboratory setting. The instrument was certain to be dropped and bumped. "The alignment was already very challenging," Fahrenkrug explains. "We have all of these very carefully placed optical parts, then we have to turn around and drop the thing and make sure it will still perform." The solution: isolating the inner optics plate from the outer housing by suspending it with elastomeric "bumpers."

In the front lines. "To be effective, we had to design SureSight so that it could be used in the front line, in the pediatrician's offices, and anywhere there are large groups of kids available for screening," explains Fahrenkrug. "Existing vision testers, autorefractors, and photoscreeners are all designed for eye-care professionals. They are expensive, difficult to use, and not child friendly. In contrast, we designed SureSight to be inexpensive, less than half the cost, and so that anyone on the staff could quickly learn to do an accurate vision screening."

During its development, and since its launch, the SureSight vision screener has already identified a significant number of children at high risk for permanent blindness at an age when treatment is still effective. "Users are so excited about their success identifying these children," Fahrenkrug says, "many of whom tested normal with other screening methods, that they go out of their way to let us know."

Additional details

Contact Drew Kugler, Welch Allyn, 4241 State St. Rd., Box 220, Skaneateles Falls, NY 13153; Tel: (315) 685-4595; E-mail: [email protected]

Other Applications

Mirror surface evaluations

Optical device verifications

Laser surgery applications

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