contact lens case reports
A Soft Lens Fit for a Difficult Keratoconus Case
BY PATRICK J. CAROLINE,
FAAO, & MARK P. ANDRÉ, FAAO
Patient K.T. is a 35-year-old software engineer with a longstanding history of bilateral keratoconus. He reported only moderate success with his lenses throughout 20 years of RGP wear. Upon initial presentation, his chief complaints were unstable VAs at distance and near with decreased lens tolerance OU.
Distance acuities with his RGP lenses were OD 20/80 and OS 20/60, pinholing to 20/60 and 20/50. Photokeratscopy and Scheinpflug photography showed excessively steep corneas of approximately 72.00 diopters (4.70 mm) OU (Figures 1 and 2). His present RGP lenses were OD 62.00 -22.25D 8.4mm and OS 63.00 -23.50D. 8.4mm.
Figure 1. Photokeratoscopy of the patient's right eye.
Figure 2. Scheinpflug photography of the patient's right eye (left), next to a normal eye (right).
Slit lamp examination revealed significant central corneal thinning with extensive stromal scarring OU and heavy apical touch OU resulting in an excessively flat lens fit. Diagnostic fitting with steeper RGP designs failed to provide a stable fitting relationship. We abandoned the RGP fit in favor of custom soft lenses manufactured by Innovations in Sight. The soft lens specifications were OD 5.60mm -29.00 14.5mm and OS 5.60mm -27.00 14.5mm. VAs were 20/50 OU (Figures 3 and 4).
Figure 3. Photokeratoscopy over the custom SCL OD, note the more regular keratoscopy mires.
Figure 4. Custom SCL OD.
We calculated the base curves using a formula we developed for adjusting the lens sagittal height fitting relationship. If the desired lens diameter is 14.5mm, add the flat K (4.70mm) to the fit factor (0.90mm). The result (5.60mm) is the soft lens base curve (Table 1).
TABLE 1: Soft Lens Base Curve Selection
|LENS DIAMETER||FIT FACTOR (FLATTER THAN K)|
|12.5 mm||0.10 mm|
|13.0 mm||0.30 mm|
|13.5 mm||0.50 mm|
|14.0 mm||0.70 mm|
|14.5 mm||0.90 mm|
|15.0 mm||1.10 mm|
|15.5 mm||1.30 mm|
|16.0 mm||1.50 mm|
Today, K.T.'s VAs are 20/40 OU, and his vision is more stable throughout the day with a 14- to 16-hour wearing time.
Patrick Caroline is an associate professor of optometry at Pacific University and 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.