Clinical Observations Of a Bifocal Soft Lens
BY DONALD S. TEIG, OD, FAAO
The Triton Soft Bifocal lens (Gelflex) is a dramatic improvement over any soft bifocal or multifocal that I have encountered over the past 10 years. I can say this because when fit correctly, this lens p
provides uncompromising acuity at both distance and near no matter how complicated the spectacle prescription. The Triton lens compensates for an impressive range of myopes, hyperopes, astigmats and presbyopes. The observations I have made of the attributes and deficiencies in attempting to successfully fit this lens are based on approximately 50 patient assessments.
Fitting The Lens
The most critical requirement for a successful fit is the 10-lens diagnostic set. I have found that the following parameters are a must in the fitting process:
- A precise spectacle prescription at distance and near
- Accurate topography K readings as well as an apical radius measurement for astigmats
- Lid aperture measurements in millimeters and an awareness of the position of the lower lid in relation to the cornea.
I fit the lens 1mm flatter than the flattest K reading. For example: 45.00 (7.50mm) flattest K=8.50mm base curve. (Note: When in doubt, usually it is better to think flatter rather than steeper; i.e. 8.60mm rather than 8.40mm).
With an astigmat, I determine the base curve by calculating 1mm flatter than the apical radius, or the median K for non-topographer owners (i.e. median K=7.40mm; base curve=8.40mm).
The secret to a well-performing Triton lens is the apposition of the flat prism-ballasted truncation of the lens with the lower lid. The ideal fit is parallel to the lower lid margin. The lens should move minimally (1 to 2mm) with the blink and when looking down to read. It is wise to over-refract with a diagnostic lens in place to assure the correct contact lens power to be ordered.
I must reiterate, this lens provides spectacular acuity at distance and near with no compromise whatsoever.
As we practitioners know, there is no panacea in contact lens designs (especially when you are talking about presbyopia). I have experienced two problems with the Triton lens. First of all, the thicker, truncated prism-ballast design can take some getting used to from a comfort standpoint. I have found that if I warn my patients to expect the worst, they usually are surprised to find out that the lens is more tolerable than anticipated. I also tell them to be prepared to gradually desensitize to the heavier feel over a period of three or four weeks. Some adapt sooner, but most adjust within a month's time. Recently the lens has been redesigned with a high water material, which reduces this discomfort significantly.
Second, unlike an aspheric multifocal soft lens design, the Triton is a true bifocal and can present some problems when viewing a computer screen. As with bifocal spectacles, you must look down to see to read. I carefully point out this fact to my Triton wearers. I advise them to adjust their computer monitors or their desk chairs so that they are looking on a downward angle when viewing the screen. Obviously, this is not a problem for patients who use laptops.
I have been wearing the Triton Soft Bifocal lens for about six weeks, and I believe it is head and shoulders better than any bifocal or multifocal soft lens that I have personally tried. My patients seem to agree. They are ecstatic about the vision they can achieve with this lens.
Dr. Teig is the founder of Sports Performance Centers of America and director of the Institute for Sports Vision in Ridgefield, CT. He is the sports vision consultant to the New York Yankees and the New York Knickerbockers.