The eyes are not only windows to the soul, they also provide a detailed look into the body. Specifically, the region at the back of the eyeball known as the fundus is the only area within the body where the network of nerves and blood vessels can be directly observed non-invasively in their natural state. Changes in the nerves and vessels of the fundus can provide clues to many disease states, including systemic (i.e. diabetes and hypertension).
But using traditional instruments, called ophthalmoscopes (first used in 1915), to gain a view of the fundus is akin to trying to read a city map through a soda straw. Seeing just one street at a time through the limited field-of-view, a doctor had to laboriously construct a complete "map" before making a diagnosis.
Now design engineers at Welch Allyn have come up with the PanOptic™ Ophthalmoscope which gives physicians a wider (25°), more panoramic view of the fundus than the previous 5° field-of-view. The Axial PointSource™ optics also increase magnification by 26%, bringing out more retinal details.
Package deal. Welch Allyn Project Leader Chris Roberts says there were several keys behind the success of the design. First was "substantial" optical and CAD modeling to achieve both cost and size goals. He specifically credits Lambda Research's (Littleton, MA) OSLO optical design software, and Pro/ENGINEER from PTC (Needham, MA). "We took a uni-body approach to the mechanical system, integrating the lenses into the package chassis to get the size and number of components down." One example is the dual-use lens nearest the eye of the patient, which focuses the illuminating light through the undilated pupil to fan out within the eye, brightening the fundus. The same lens shapes and directs the image of the fundus back to the physician.
The dual-use lens negates the need for a beam splitter in the optical path to reflect the source light into the patient's eye and then transmit the fundus image to the doctor. With a loss on the order of 50% each time light passed through the splitter, the doctor would have only 25% of the light available, requiring a nearly 50W source with both size and thermal issues. The elegant solution uses a fully reflective, small mirror placed slightly offset from the optical axis and hidden in a zone where the physician's vision is not focused (see figure).
"Manufacturing technology improvements have lead to high precision, molded acrylic and styrene lenses as a commodity, lowering cost," adds Roberts. The team spent time with key vendors to both challenge them and understand their processes for the design advances needed, he notes. Welch Allyn also does machining in-house to lower the cost of precision components.
As another example of the ophthalmoscope's utility, Dr. Mark Swartz, a professor of medicine at Mt. Sinai School of Medicine (New York, NY) notes, "By offering a wider view of the fundus, the PanOptic Ophthalmoscope allows a new view of the retina that was previously only available using an indirect ophthalmoscope through a dilated pupil."
|Contact Chris Roberts, Welch Allyn, 4341 State Street Rd., Skaneateles Falls, NY 13153-0220; Tel: (315) 685-2588; Fax: (315) 685-2546; E-mail: firstname.lastname@example.org ; or Enter 503