contact lens case reports
A Rare Keratoconus Fit
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO

Figure 1. Photokeratoscopy and videokeratograpy of the patient illustrating the unilateral nature of his keratoconus.
Figure 2. Apical thinning OD, normal OS.
Figure 3. Slit lamp photography illustrating lack of corneal scarring OD.
Figure 4. KBA lens design OD.

Patient GR is a 73-year-old retired biochemist who has a long-standing history of unilateral keratoconus in his right eye. He first learned of his condition during a routine military entrance examination at age 18. Since that time, he had elected to forgo any form of contact lens correction OD and instead relied solely on his left eye for functional vision. GR presented to our clinic interested in a possible contact lens for his right eye because of increasing cataract formation in his left eye.

A Rare Find

We deferred manifest refraction in his right eye because of the advanced nature of the keratoconus. Manifest refraction in the left eye was ­0.50 ­1.25 x 25 with a visual acuity of 20/30. Simulated keratometric readings were OD 59.50 @ 22/70.50 @ 112 and OS 43.00 @ 180/43.12 @ 90 (Figure 1).

Slit lamp examination OD showed significant apical thinning, typical of an eye in the advanced stage of keratoconus (Figure 2). Perhaps the most notable feature OD was the complete lack of any corneal scarring (Figure 3).

This patient demonstrates two rare findings in severe keratoconus: 1. a true unilateral manifestation; 2. an advanced form of the condition void of many of the common slit lamp findings such as corneal scarring (ruptures in Bowman's layer), vertical striae and Fleischer's ring.

Fitting the Patient

We subsequently fit GR with the bi-aspheric KBA lens design (Precision Technology Ltd., Vancouver, BC). Lens parameters were base curve of 4.8mm (70.00 diopters), ­19.50D power, 10.2mm diameter and a posterior eccentricity of 1.3 (Figure 4). Visual acuity with the lens was 20/40.

The bi-aspheric design of the KBA allows the central aspheric portion of the lens to fit with slight apical clearance while the second aspheric zone allows for lens clearance across the flatter midperipheral cornea.

GR successfully wears the lens during waking hours and enjoys his newly acquired binocular vision.

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

Mark André is director of contact lens services at the Oregon Health Sciences University and serves as an adjunct assistant professor of optometry at Pacific University.