Comfort for the Keratoconus Patient: A COMPARISON OF LENS DESIGNS

BY SUE CONNELLY, FCLSA, & DIANE BROE, FCLSA
May 1999

This article explains why the ComfortKone contact lens design stands out among the rest.

In some cases, successfully fitting patients with keratoconus seems more of a surprise than a predicted result. Their unusual corneal topographies demand complicated contact lens designs that often require the intuition of an artist rather than the skill of a scientist. However, a revolutionary new lens design, the ComfortKone by Metro Optics, Inc., has helped take much out of the mystery and guesswork in fitting these patients. This design uses state-of-the-art technology, for a lens that is easy to fit and easy to reproduce for the practitioner and, most importantly, easy to wear for the patient.

The ComfortKone Lens Design

The ComfortKone incorporates triaspheric curves to maximize the overall alignment of the lens to the cornea. The lens begins with a spherical central optic zone, which fits the apex of the cone and provides excellent optics. It then flattens into the aspheric "A" curve, considered the fitting curve of the lens. The "A" value represents the difference between the base curve and the peripheral curve, with the higher "A" values representing greater rates of flattening.

The ComfortKone can be designed successfully with diagnostic contact lenses and a complete fitting guide or with corneal topography and the consultation team at Metro Optics. We used the 18-lens diagnostic set and fluorescein pattern interpretation to design contact lenses.

Evaluating Patients with Keratoconus

Since the ComfortKone lens design was introduced to our practice, it has become easier to fit keratoconus patients. To document this process, we compared the first 10 patients fit with the ComfortKone design in our practice with a random sample of 20 previously fit keratonconus patients.

The six female and four male patients receiving ComfortKone lenses were 16 to 52 years of age. Seven were diagnosed before the new lenses were fit and were wearing another lens design. Three were newly diagnosed. Nine women and 11 men, ranging from 22 to 60 years of age, were fit with other lens designs. Six of these patients were diagnosed and fit with keratoconus lenses for the first time at our clinic.

Before the ComfortKone was introduced, we used a variety of special keratoconus lens designs, including Rose K, Soper cone, McGuire cone and Envision lenses, and they served practitioners and patients well. Each lens design had its unique inherent learning curve, which is expected when fitting any type of contact lens and may be unavoidable when fitting a complex design for keratoconus.

For patients wearing other lens designs, we had to order an average of 2.5 lenses per eye for success. However, with the ComfortKone, we only had to order an average of 1.5 lenses per eye for success, even for first patients. Relatively basic lens designs may require a learning curve of 1.5 lenses per eye in the initial analysis, so to achieve this success with complicated keratoconus corneas is remarkable. This ease of fitting positively impacts patients' perceptions about their experience, and directly affects practitioners' chair time and financial investment.

Among the 20 patients with other lens designs, 12 required a design change (e.g., Soper cone to Rose K, McGuire cone to Soper cone) before fitting was successful. However, a design change wasn't necessary for any of the ComfortKone patients.

Controlled Posterior Surface

The ComfortKone's success may be attributed in part to the control of the posterior surface of the lens. Through years of research and design experience, Metro Optics created a contact lens design that leaves fewer variables to fit. With the ComfortKone, the optic zone size and peripheral curve system are controlled, leaving only the base curve, power, diameter and "A" value to be determined by the lens professional.

Although some lens professionals prefer to control the optic zone size and peripheral curve system, these variables can complicate the fitting process, potentially leading to missteps and errant lenses even for the most adept fitter. Custom parameters are available, but our experience has shown that control of the posterior surface can help eliminate errors and streamline the fitting process for busy practices (Fig. 1).

Lens Duplication

Generation of the posterior surface by computer-controlled lathes and the control of parameters allows exact duplication of lenses. For many years, special keratoconus designs were lathed and polished by hand, creating wonderful, unique works of art. Although these lenses may have fit like a glove, they were nearly impossible to reproduce. When one of the 20 patients who were not wearing ComfortKone lenses wanted to replace a lost lens, it took seven lenses to find the closest reproduction of the original lens, even though we had the parameters. Many labs alter the posterior parameters of "standardized" keratoconus lens designs to improve the lens-to-cornea relationship. Although this is an admirable goal, it makes it difficult to reproduce lens designs between labs or within the same lab several years later. Reproducibility is invaluable when coping with the differences between a diagnostic lens and patient lens, an original lens and replacement lens, and lenses ordered from different practices.

Ease of Fitting for All Practitioners

Control of the posterior surface makes it easy for practitioners of varying expertise to fit ComfortKone lenses. In evaluating ComfortKone success rates, we found no significant difference between novice and experienced keratoconus fitters. Metro Optics provides a comprehensive fitting guide that walks a novice fitter through the steps, simplifying a process that can often be intimidating for new fitters. Because the ComfortKone is easy to fit, it can be as beneficial to a practice with few keratoconus patients as it is to a practice with many.

Patient Acceptance

Although reduced chair time, excellent reproducibility and a streamlined initial fit are important characteristics, in our experience, one of the greatest attributes of this lens design is its acceptance by contact lens wearers. Patients who were uncomfortable with previous lens designs were extremely pleased with the initial and long-term comfort of the ComfortKone lens. Those who experienced corneal irritation from previous contact lenses commented on greater comfort even with the diagnostic lenses.

The contact lens industry is benefiting greatly from enhanced tools created by manufacturers who understand lenses from a different perspective -- the posterior side. Innovative designers use state-of-the-art equipment to generate technically superior designs such as the ComfortKone. The introduction of this lens to our practice has streamlined the fitting process, reduced chair time and increased patient satisfaction for keratoconus patients.

Sue Connelly is a contact lens professional at Park Nicollet Clinic in Minneapolis, Minn. She is also the educational consultant for the Contact Lens Society of America.
Diane Broe is the contact lens department supervisor at Park Nicollet Clinic in Minneapolis, Minn. She also serves as the president-elect of the Contact Lens Society of America.