Contact Lens Design & Materials
Developments in Soft Lens Options for Keratoconus
BY NEIL PENCE, OD, FAAO
While the large majority of contact lenses prescribed for patients who have keratoconus are GP lenses, there has always been a role for soft contact lenses to play. Early forms of keratoconus may be corrected with soft lenses, often with correction for astigmatism. Soft contact lenses may also be employed in an occasional piggyback system. Finally, there are custom soft contact lenses specifically designed for patients who have keratoconus.
This column reviews recent changes and additions to this last category.
Established Lens Design, New Material
X-Cel Contacts has produced the Flexlens series of specialty soft contact lenses for many years. One of the lenses in that line is the Tri-curve design intended for patients who have keratoconus. This lens design is available in a wide variety of custom parameters. Another design is also available intended to be used in piggyback fits.
All of the custom contact lenses from X-Cel Contacts are now available in the Definitive material manufactured by Contamac. This latheable silicone hydrogel material allows more oxygen to be transmitted through the lens as compared to through lenses manufactured in traditional hydrogel materials.
Alden Optical introduced NovaKone soft contact lenses for correcting keratoconus and possibly other corneal irregularities. The lens design has standard parameters, but is highly customizable for diameter, base curve, and center thickness. A steep base curve is generally employed to vault the cornea, similar to a GP lens fit. If an acceptable correction cannot be achieved, the lens center thickness can be increased up to four steps to attempt to correct more irregularity. It is likely that the final correction will be a toric lens.
A second new design is KeraSoft IC, introduced into North America by Bausch + Lomb (B+L) and manufactured in the Definitive material. This design employs a fairly novel approach. Rather than using steep base curves to attempt to vault the cornea and create a tear lens to correct the irregular vision, this lens uses relatively standard soft contact lens base curves. When centration and movement are optimal for a good fit, the optical correction is placed on the front of the contact lens to correct vision. Again, highly astigmatic corrections are often needed.
Owing to its unique fitting approach, practitioners must complete online training modules and become certified fitters prior to ordering KeraSoft IC lenses. The training modules can be accessed through the websites of B+L (www.bausch.com) or Art Optical (www.artoptical.com, a manufacturer of the lens). An eight-lens fitting set is then available to begin using the KeraSoft IC lens.
It is beneficial for specialty contact lens fitters to have as many options as possible to fit the often challenging patients who have corneal irregularities such as keratoconus. These new developments are welcome additions to the total “toolkit” and play a big role in fitting patients who are more intolerant to GP lenses. The increased comfort and easier adaptation are generally gained at the cost of slightly reduced best visual acuity.
On a precautionary note, these are all very thick soft contact lens designs. The ability to utilize the Definitive material is a plus, but patients fit into these lenses still require consistent monitoring of the limbal vessels for any possible signs of hypoxia problems. CLS
Dr. Pence is the associate dean for Clinical and Patient Care Services, Indiana University School of Optometry in Bloomington, Indiana. He is also a consultant to B+L, J&J Vision Care, and Alcon. You can reach him at pence@indiana. edu.