orthokeratology today
How Fit is Your Patient for Orthokeratology?
BY EEF VAN DER WORP, BSC, FAAO, FIACLE

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.

Ametropia

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 limbal) cor-
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.

Pupil

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.

Contraindication?

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 Netherlands.