Contact Lens Design & Materials
Replacing Discontinued Lenses
By Neil Pence, OD, FAAO
When particular contact lenses are discontinued, or if manufacturing factors cause significant delays, it can be challenging to find suitable replacements. Fortunately, the contact lens industry continues to offer options to meet the needs of these patients.
Probably most offices have wearers who have resisted efforts to be refit into newer generations of lenses. When the original lens is no longer produced, the patient is generally more accepting of a new brand. Whenever possible, it is best to use options that can be obtained quickly and are likely to be available for quite some time.
For patients who need something outside of the parameters of mass produced options, cast-molded lenses and custom soft contact lenses continue to be readily available. Many manufacturers make spherical soft lenses in a wide range of powers, base curves, and diameters. Finding suitable replacements for high-cylinder lenses seems to be more problematic. Each design may differ in thickness, diameter, and the amount or effect of the prism ballasting, all of which can affect lens rotation/rotational stability.
For many custom high prescription lenses—and especially for thicker toric designs—oxygen transmission can be a concern. Some spherical patients benefited from the increased oxygen allowed by the O2 Optix Custom (Ciba Vision), but this is no longer an option. There is a latheable silicone hydrogel material available, the Definitive material (Contamac), that allows more oxygen transmission for these custom designs than with hydrogel materials. Table 1 lists some companies that supply custom toric soft lenses.
Prosthetic contact lenses can be another challenge when comes to finding replacements. Trying to mimic a discontinued or unavailable lens can be difficult. Lenses that had dark under printing to help function similar to an iris in blocking out light perhaps an aniridia patient are ten difficult to duplicate. The companies listed in Table 2 all produce prosthetic contact lenses and may be good places to look when needing to duplicate prosthetic lenses.
Finally, one technique to consider when faced with delays in replac ing custom or prosthetic contact lenses is piggybacking of two soft lenses. While this may sound un usual, and piggybacking usually means a GP on top of a soft lens, two soft lenses can be piggybacked as well. As a temporary ternative, two normal-production opaque tinted lenses can be piggybacked to provide a darker iris area and to somewhat mimic the darker underprinting effect. Likewise, two soft lenses might be piggybacked to come close to the effect of very high-powered custom lenses.
This can supply functional vi sion in short-term cases and has been surprisingly comfortable and trouble free in more than a handful of patients. CLS
Dr. Pence is the associate dean for Clinical and Patient Care Services, Indiana University School of Optometry in Bloomington, Indiana. He is a consultant or advisor to B+L, Ciba Vision, and Vistakon and has received research funding from AMO. You can reach him at email@example.com.