BU College of Engineering Magazine
Spring 2004
Vision Science
Recognize this conversation?
“One. Two.”
“Ummm…”
“One. Two.”
“One? One. Yeah, one.”
“Okay. Is three better? Or four?”
“Can you go back?”
“Here we go. Three. Four.”
“Four. Maybe. Maybe the same?”
Chances are your grandchildren will only recognize this frustrating and often rushed conversation during an eye exam if you tell them about vision science before their time. That’s because BU and Boston Micromachines Corporation (BMC) have contributed to the creation of an award-winning MEMS-based Adaptive Optics Phoropter (MAOP). Their efforts to improve vision science were rewarded in September 2003 with a Research and Design Magazine 100 Award for Life Science, given to the year’s top technological innovations. Past winners have included such civilization-defining technologies as the refrigerator.
A traditional phoropter consists of a number of different glass lenses, and an ophthalmologist or optometrist relies on a patient to choose between two different choices. A patient gives subjective responses to progressively smaller differences between possible lens choices. The examiner uses the property of refraction to determine the level of farsightedness, nearsightedness, astigmatism and presbyopia.
The award-winning MAOP uses wavefront sensors and BMC’s deformable mirrors instead of glass lenses, to do everything a traditional phoropter can—more quickly, less subjectively, with less manual effort by the examiner, all while addressing higher-order aberrations of the eye. The new device will eventually be small and inexpensive enough (and even mobile on a cart) to be used in a clinical setting. It is already a fraction of the size of the piezo-stack adaptive optics phoropter that preceded it.
The MAOP works by passing a beam from outside the eye through the lens of the eye and to the retina. The light passes out again through the eye’s lens and onto an array of small lenslets. The lenslets focus the light on a CCD detector, creating a map of the aberrations in the eye’s lens. A processor determines the correction needed to the detected wavefront and sends signals of different voltages to the appropriate structures on the deformable mirror. The deformable mirror changes shape and corrects the image seen by the eye.
The final instrument may not look much different than a traditional phoropter, but clinicians and patients will notice that determining the needed correction is quicker and requires less effort. Prescriptions will be more accurate for not being limited to the finite number of corrective lenses available in the traditional phoropter. “Slowly, by using our mirror, you are changing the defocus term,” explains Bierden. “Then you are changing the astigmatism term. Then you are going up in order of aberrations.” Paul Bierden, BMC’s president and CEO, says that subjects examined with the MAOP typically report clarity and crispness unattainable without the use of adaptive optics.
Eyeglasses, contact lenses, and even laser refractive surgery currently only correct for the two problems of defocus and astigmatism and ignore “higher-order” aberrations such as coma and spherical aberrations, in part because of the difficulty of measuring the aberrations. MAOP will allow doctors to accurately measure those aberrations and also to image the surface of the retina, providing the ability to better treat afflictions including retinitis pigmentosa, glaucoma, diabetic retinopathy, and macular degeneration. All of these afflictions are likely to become more prevalent in the aging and increasingly diabetic American population. Even people with accurate current prescriptions will likely see their vision improve as vision correction technology catches up with the information on higher-order aberrations that the new phoropter will make available. Bausch & Lomb has reported on efforts towards manufacturing custom contact lenses based on information from MAOP eye examinations. The system would record the voltage profiles across the deformable mirror and then send them via the Internet to a distant manufacturing facility, where a machine would diamond-turn custom contact lenses and ship them next-day mail. The customer would receive perfect, custom lenses the day after the examination. “That’s the vision,” says Bierden.
“The traditional phoropter has been around for 100 years. The real key to improving it was the deformable mirror,” says Tom Bifano, ENG professor and CTO of BMC. “It was powerful for us because it represented the first time our mirrors were being praised not for being mirrors but for achieving some function. When the team working on the MAOP went to choose a mirror, there was no bid. There was only one mirror to choose for this application—BMC’s.”
The MAOP was developed by a team of researchers at Boston Micromachines; Lawrence Livermore National Laboratory; Bausch & Lomb, Rochester, NY; Sandia National Laboratories, Livermore, CA; University of Rochester, NY; and Wavefront Sciences, Albuquerque, NM. BMC is presently working to further refine the deformable mirror used in the MAOP and looking forward to clinical trials in the near future with Bausch & Lomb.
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