contact
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.
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Figure 1. EH's pre-fitting (left) and post-fitting
(right) topographies. |
For Example
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.
Contact Lens Spectrum, Issue: November 2006