How Fit is Your Patient for
BY EEF VAN DER WORP, BSC,
It's estimated that three years
after the introduction of overnight orthokeratology in the Netherlands, roughly
13,500 people are using this modality (in a population of 16 million), often
with high levels of satisfaction. What makes orthokeratology work in the
Netherlands? For one, practitioners need a full day of hands-on training before
starting orthokeratology and also, corneal topography is mandatory.
People frequently ask, "What kind of lens
type is used in the Netherlands? Is the lens fit the secret to success?"
Personally, I think the question, "How fit is the patient?" is more important.
Deciding whether a candidate is suitable for orthokeratology is probably the
most essential part of the entire fitting procedure.
In general, practitioners in the Netherlands are
cautious with higher amounts of myopia (this is especially true for
practitioners just starting orthokeratology). The FDA has approved
orthokeratology for up to �6.00D, but in the real world �4.00D is often the
maximum possible. Astigmatism correction has limitations as well. Currently,
only moderate (up to 1.50D), with-the-rule, central (as opposed to limbal to
neal astigmatism can be corrected, although studies in Europe
with toric orthokeratology lenses show promising results for correction of
astigmatism up to 3.00D. Possibilities for correcting hyperopia and presbyopia
are being investigated, but inexperienced fitters are probably better off
avoiding such fits. For monovision, a good strategy is to create full correction
for both eyes first, then keep the eye with the most satisfying visual outcome
for distance while adjusting the prescription of the other eye for near.
Does pupil size matter? Yes. Should you use it to
exclude patients up front? Usually no. You should take the anterior chamber
depth into account as well. Eyes with deep anterior chambers use a larger
portion of the cornea and the combination of this and a large pupil might cause
problems at night (but even this is often acceptable for patients). In children,
large pupils usually do not interfere with their daily routine.
Contact Lens Wearers
It's important that current lens wearers return
to their baseline corneal topography before entering the procedure.
Unfortunately, this can take about three weeks in GP lens wearers and at least
three days in hydrogel lens wearers, but sometimes much longer. Risk factors are
low-Dk materials, decentered lens fits and back-aspheric bifocal GPs.
Theoretically there are anatomical and
physiological factors to consider, but they usually don't lead to immediate
disqualification. Deep set eyes and abnormal eyelids might be more challenging
in terms of corneal topography. Severe dry eyes can also lead to unreliable
topography maps as well as an increase in debris buildup and a higher risk of
lens binding. However, many marginal dry eyes can benefit from orthokeratology
because there's no lens in place during the day, so marginal dryness often is an
indication rather than a contraindication. True contraindications for
orthokeratology include standard pathological eye conditions (this includes
keratoconus), just as with any contact lens fit.
A Good Fit
Make sure your patient is fit before fitting
orthokeratology. It prevents disappointment for you and the patient. Ortho-k
fits many people's lifestyles, and if it fits it can change their lives.
Dr. van der
Worp is a lecturer at the school of optometry of the Hogeschool Utrecht and a
researcher at the University of Maastricht � department of ophthalmology in the
Contact Lens Spectrum, Issue: March 2006