contact lens case reports
Peripheral Lens Design is Key to GP Comfort
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Beasy to see the smoothness of the ack in "the day," our contact lens mentors taught us the clinical importance of peripheral lens design and contour with rigid contact lenses. Today, our students and residents are continually amazed by the change in patient comfort from, "I can't wear this lens at all" to, "I can't even feel the lens on my eye," a transformation that can result from the simple technique of blending. It is clear (if we simply listen to our patients) that this is one of the key elements to GP lens comfort.
With today's modern lathing techniques, the peripheral lens design (spherical, aspherical, or tangent angles) is programmed into the lathe to create a smooth, seamless lens periphery. We would like to believe that modern lathes have eliminated the blending problem…but that is not always the case, especially in more custom lens designs.
Evaluating the Lens Periphery
In the past, one of the greatest obstacles to understanding peripheral contact lens contour was practitioner viewing, in that it's a difficult parameter to see and quantify. In 1963, Joseph Soper described visualization of the contact lens periphery through a fluorescent tube reflection technique, and in the late 1970s Erich Koeniger developed the Profile Analyzer, a more controlled and mechanized version of the fluorescent tube technique (Figure 1). Unfortunately, this unit went out of production many years ago.
Figure 1. The Profile Analyzer.
At Pacific University, we developed a hybrid viewing technique by modifying a traditional Burton Lamp, opaquing one bulb completely with black electrician's tape and on the other bulb leaving a 1.0mm slit for the white light to project (Figure 2). The contact lens is held beneath the lamp using a DMV device (concave-side-up), and the slit of light is positioned over the lower one-third of the contact lens. It is easy to see the smoothness of the posterior periphery by the "J" pattern when viewing through the magnifying window of the Burton Lamp. Any abnormalities or junctions on the posterior surface will show up as a small "stairstep" pattern (Figure 3).
Figure 2. The modified fluorescent tube Burton lamp technique.
Figure 3. Lens periphery viewed with Burton lamp technique.
Dr. Rodger Kame once said, "if you can see them…the patient can feel them." Therefore, we need to monitor the posterior lens geometry so that we can communicate any sub-optimal findings to our laboratories. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.