Contact Lens Case Reports
Soft Designs for Keratoconus
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
The concept of using soft contact lenses to correct keratoconus dates as far back as the early 1970s, with the “off-label” use of the original 13.5mm soft lens, the Bausch + Lomb (B+L) “C” series. This lens was somewhat ideal for ectatic corneas because with the spin-cast technology of the time, the base curve radii steepened as the anterior power increased (Table 1).
|LENS POWER||BASE CURVE RADIUS|
The first FDA-cleared soft contact lens for keratoconus was manufactured by Flexlens. On Jan. 4, 1979, the FDA provided its first (and only) full spectrum clearance for soft contact lenses. It stated that “the Flexlens soft contact lens is indicated for the correction of any atypical ametropias with either normal or abnormal refractive errors.” This one-of-a-kind clearance allowed Flexlens to manufacture any contact lens shape or power for any condition from normal eyes to those with complex ocular conditions.
Since then, several custom soft contact lens manufacturers have developed or distributed soft lenses for keratoconus. In the United States, these include Flexlens (X-Cel Contacts), Soft K (Advanced Vision Technologies), NovaKone (Alden Optical), KeraSoft IC (B+L) , YamaKone IC (C&E Vision Services, Inc.), and Hydrakone (Visionary Optics, LLC).
Keratoconus and GP Intolerance
A 32-year-old patient was referred to us with the diagnosis of keratoconus and GP lens intolerance. At that time, we fitted the patient with the Soft K lens from the 14.2mm, three-lens diagnostic set, which has radii of 7.30mm, 7.60mm, and 7.90mm; it is also available in radii of 7.00mm and 8.30mm. The lenses were manufactured in the Contamac Definitive silicone hydrogel material with a Dk of 60. The lenses incorporate a fenestration in the midperiphery to control the fluid pressures present beneath these thicker lenses (Figure 1).
Figure 1. The Soft K lens design.
With lenses of OD 7.60mm base curve, 14.2mm diameter, –6.50D power, 0.40mm center thickness and OS 7.90mm base curve, 14.2mm diameter, –2.25D power, 0.40mm center thickness, the patient was able to achieve all-day comfort and visual acuities of OD 20/30 and OS 20/25 (Figures 2 and 3).
Figure 2. Patient with the Soft K lenses for keratoconus.
Figure 3. On-eye OCT image of the Soft K lens, center thickness 0.40mm.
This case, and others like it, clearly shows that soft contact lenses can be effectively used in some cases of keratoconus. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant for Contamac. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.