contact lens case reports
Soft Lenses for Keratoconus
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
For the past 100 years, rigid corneal contact lenses have offered the best visual correction for patients who have keratoconus. However, with all of their benefits, modern GP lenses may not meet the primary needs — particularly comfort and all-day lens wear — of all patients.
Intuitively, it seems unlikely that soft contact lenses could correct the complex refractive error associated with keratoconus, but new soft lens designs and manufacturing techniques might be changing that perspective.
Figure 1. Corneal topography and custom keratoconus soft lens design from MedLens Inc.
Why Soft Contact Lenses?
Clinical experience has demonstrated that a small subset of keratoconus patients may experience a corneal hypersensitivity in certain stages of their condition. This hypersensitivity may be due, in part, to a dilatation or stretching of the corneal nerve fibers; in addition, minute ruptures in Bowman's layer may be a contributing factor. This subset of patients may find it difficult, or even impossible, to tolerate well-fitted GP lenses.
Soft Designs for Keratoconus
A viable option is to use one of the many custom toric soft contact lenses we currently have at our disposal. These have proven successful in the early stages of the condition or in form fruste keratoconus.
However, custom soft spherical lenses may also prove greatly successful. These lenses incorporate a tricurve posterior lens design with increased central thickness to mask much of the regular and irregular astigmatism. You can custom design these lenses using a broad range of base curve radii, powers, diameters and center thickness values.
Our patient was a 26-year-old male with a long standing history of keratoconus and a growing intolerance to his well-fitted GP lenses. His central keratometric readings were OD 55.00 @ 084/61.50 @ 174 with an apical curvature of 68.50D (4.95mm), OS 46.00 @ 030/51.75 @ 120 with an apical curvature of 59.50D (5.65mm). We began the fitting procedure by selecting a diagnostic lens with a base curve radius 1.00mm flatter than the mean K in millimeters. In our case, the right eye had a mean K of 58.25D or 5.80mm, so we selected a diagnostic lens of 6.80mm. The left eye mean K was 49.00D or 6.90mm, and the diagnostic lens selected was 7.90mm (Figure 2).
Figure 2. Custom keratoconus soft lenses OU.
The thicker soft lens design is substantially stiffer than a traditional soft lens; therefore, an actual tear lens will form between the posterior surface of the lens and the cornea. This lacrimal lens helps correct the regular and irregular astigmatism. We determined the final lens power by a spherocylinder over-refraction over the diagnostic lens.
Our patient achieved all-day comfort (14 to 16 hours) and 20/30 vision OD and OS with the keratoconus soft lenses and a 2.50D residual cylinder spectacle correction. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences and SynergEyes, Inc. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision and SynergEyes, Inc.