lens case reports
Steepening Corneal Curvature through Overnight Ortho-k
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRé, FAAO
The first thing that probably comes to mind when you think about modern contact lens cornea reshaping is flattening the anterior surface of the cornea for correcting myopia. An often overlookeed technique is that of steepening the central cornea for correcting hyperopia. Clinical experience has taught us that corneal tissue (predominately the epithelium) is incredibly responsive and will go to wherever we ask it. The posterior design of a corneal reshaping lens determines the amount, direction and speed of tissue movement. To steepen the central cornea, three design features should be present on the posterior surface of the lens:
1. An apical clearance zone.
2. A contact zone 2mm to 3mm from the geometric center.
3. A relief zone in the midperiphery.
A Step Further
Another refractive anomaly that lenses designed to steepen the cornea can address is that of presbyopia. Perhaps our greatest usage for these lenses has been for managing emmetropic patients who are now presbyopic. It's no surprise that presbyopic patients who have enjoyed 20/20 uncorrected vision throughout life often find it difficult to adjust to their new dependency on reading glasses. While our main treatment option for such individuals continues to include a wide range of presbyopia-correcting rigid and soft contact lenses, some presbyopic patients experience suboptimal vision as well as dryness and decreased comfort with the daily wearing of contact lenses. For some of these patients, we've used an overnight corneal reshaping lens to steepen the radius of curvature of one eye only, to create a functional monovision.
|Figure 1. EH's pre-fitting (left) and post-fitting (right) topographies.|
A case in point is patient EH, a presbyopic male with a lifelong history of perfect, 20/15 uncorrected distance visual acuity. As with many emmetropes, his ongoing experience with presbyopia has been unpleasant. We fit a wide range of multifocal soft and GP lens designs, but EH's visual acuity was always distorted at distance and near.
We then introduced EH to the concept of overnight corneal reshaping (of one eye only), and the technique intrigued him. We subsequently fit him with the corneal steepening Paragon CRT lens design, which steepened his cornea approximately +2.00D (Figure 1). EH has been extremely pleased with his new freedom from the daily wearing of glasses and contact lenses. His distance visual acuity remains 20/15 through his uncorrected eye and 20/15 at near through his overnight corneal reshaping eye.
The More Options, The Better
This is but one more option we can offer our presbyopic patients as we attempt to address the complex psychological, optical and anatomical issues associated with the aging eye.
Patrick Caroline is an associate professor of optometry at Pacific University and is an assistant professor of ophthalmology at the Oregon Health Sciences 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 Alcon Labs, CooperVision and SynergEyes, Inc.