contact lens case reports

Aspheric Design Manages Monocular Keratoconus

BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRE, FCLSA
OCTOBER 1998

Throughout the years, a wide range of contact lens designs have been developed to address the asymmetric and irregular corneal topographies of keratoconus. The primary objective of most keratoconus lens designs is to provide a small diameter, steep central radius to address the central or paracentral corneal ectasia as well as to provide a series of progressively flatter radii to clear the flatter peripheral cornea. These design objectives were previously accomplished with multiple spherical radii which were blended together to form the desired flattening contour. More recently, precision aspheric lathing and polishing technology has allowed more sophisticated shapes to be produced with accuracy measured in microns.

Bearing It No More

A 24-year-old woman presented with clinical findings of keratoconus in her right eye only. Her uncorrected visual acuities were 20/300 OD and 20/20 OS. Central keratometric readings were OD 45.37 @ 42/47.87 @ 132 and OS 42.87 @ 156/43.62 @ 66. The manifest refraction OD was -4.50 -2.25 x 36, 20/30 and OS was plano -0.50 x 160, 20/20. Slit lamp examination was within normal limits OU except for faint, central, vertical striae OD only. Corneal mapping demonstrated a steep, 4.0 to 5.0mm central ectasia surrounded by nearly 360 degrees of normal (flatter) corneal topography (Fig. 1).

FIG. 1:  Corneal mapping of the patient's right eye.

Numerous keratoconus lens designs were diagnostically fitted, which resulted in excessive apical or midperipheral bearing. To overcome these obstacles, we fitted the patient with the Aspheric 20 H design from Contex Laboratories (Fig. 2). The final design had a 7.00mm base curve, power of -4.00D, diameter of 10.2mm and a visual acuity of 20/20.

FIG. 2:  Fluorescein pattern of the Aspheric 20 H on the patient's right eye.

Aspheric To the Rescue

The Contex Aspheric 20 H diagnostic set has been a welcome addition to our armamentarium of keratoconus design options. Its design incorporates a series of progressively flattening aspheric radii to create the desired lens clearance across the flatter midperipheral and peripheral corneal topography (Fig. 3). We have found that the Aspheric 20 H diameters of 9.2 and 10.2mm, which are unique in keratoconus lens designs, permit initial and long term comfort superior to traditional lens designs. This is especially true in cases of early keratoconus, or in cases such as ours where the lens is worn monocularly.

FIG. 3:  The multizonal aspheric posterior shape of the Aspheric 20 H design from Contex Laboratories.

Patrick Caroline is an assistant professor of ophthalmology at the Oregon Health Sciences University and an assistant professor of optometry at Pacific University.

Mark Andre is director of contact lens services at the Oregon Health Sciences University.