Contact Lens Case Reports
Using a Corneal Design to Manage Keratoconus
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
An 18-year-old female was recently referred to our clinic with a diagnosis of bilateral keratoconus and no history of contact lens wear. Corneal topographies were performed and the elevation maps evaluated to determine the height differentials across the corneas. This technique was described in our April 2015 Case Reports column in which we noted that patients who have less than a 350-micron height differential had an 88% chance of being successfully fitted with a corneal contact lens design.
This patient demonstrated a height differential of 379 microns OD (Figure 1) and of 372 microns OS (Figure 2). Despite the “borderline” height differential, we chose to fit aspheric corneal GP lenses (Figure 3).
Figure 1. Axial and elevation display maps of the patient’s right eye.
Figure 2. Axial and elevation display maps of the patient’s left eye.
Figure 3. Corneal topographies and fluorescein patterns of the aspheric corneal lenses. Top images right eye; bottom images left eye.
Corneal Versus Scleral
Why a corneal and not a scleral lens design? Our industry has enjoyed a 65-year history of corneal lenses in which millions of patients have experienced long-term success unrivaled by any other lens modality. When fitted properly, these lenses—with their high Dk, movement, and tear exchange—exhibit very few long-term complications.
Our research at Pacific University has shown that there is still much we don’t know about contemporary scleral lenses:
1. How much corneal swelling takes place beneath a scleral contact lens over a 12-hour period?
2. How much tear exchange takes place beneath a scleral lens?
3. Are there long-term effects of scleral lenses on the cornea, limbus, conjunctiva, and sclera?
4. Should scleral lenses be designed to clear (vault over), or should they land on, the cornea and/or limbus?
5. What is the optimum post-lens tear film thickness for a scleral lens?
6. What is the actual shape of the sclera, and is it asymmetrical?
7. Is saline (with a its lack of nutrients for the cornea and conjunctiva) the optimum post-lens solution?
8. How do we best manage the unique scleral complications of tear film fogging, conjunctival prolapse, epithelial bogging, conjunctival compression, post-lens debris, and post-penetrating keratoplasty corneal edema?
So, when fitting irregular corneas, we continue to promote to our students, first and foremost, the fitting of corneal contact lenses. We remain advocates of scleral lenses, but reserve them for patients who have ocular surface disease or when the cornea exhibits asymmetric height differences that prohibit successful fitting with a corneal lens design. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Contamac. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.