Article Date: 5/1/2003

orthokeratology
Orthokeratology:The Bare Facts
It's the right time to consider Ortho-K and fully inform patients about this alternative to refractive surgery.
BY KENNETH A. LEBOW, O.D., F.A.A.O., Virginia Beach, Va.

Thanks to new rigid contact lens materials; new, unique lens designs; advances in corneal measurement technology; and revisited contact lens fitting approaches, we now have many more contact lens options to offer our patients.

These contact lens choices are especially significant when you're dealing with a patient who's considering refractive surgery alternatives to more permanently correct his ammetropia.

For the purpose of this article, I'll discuss the finer points of orthokeratology and what you should know about it.

ILLUSTRATION BY MICHAEL LOTENERO

Knowing the basics

Vision care experts have defined contemporary orthokeratology (also referred to as corneal molding) as the temporary reduction in myopia by the programmed application of rigid gas permeable (GP) contact lenses.

Recent contact lens design advancements have accelerated the corneal reshaping process and now often only one or two pairs of lenses are required instead of four to six pairs for the complete process. But how does the process of contact lens induced corneal reshaping compare with the surgical alteration of the corneal tissue?

The following sections, beginning with a topographical viewpoint, will reveal the differences between the two procedures.

Topographically speaking

From a topographic viewpoint, both orthokeratology and refractive surgery change the normal prolate corneal geometry to an oblate shape, thus reducing the eye's axial length and subsequently improving the focus for myopes.

Presumably, corneal reshaping accomplishes this change in corneal geometry by redistributing and thinning the central corneal epithelium while concomitantly thickening the peripheral epithelium (Swarbrick, et. al. 1998). This effect helps explain the relative flattening of the cornea associated with corneal molding. Most refractive surgery procedures actually remove stromal tissue to produce a more permanent effect. So what happens if orthokeratology produces a result with which you or your patient aren't satisfied?

No surgery? No worry.

First off, the main point to keep in mind is that orthokeratology is reversible, regardless of whether we're talking about results or complications.

Making adjustments. Relatively simple adjustments to either the base curve of the contact lens or to the patient's wearing time can rapidly and accurately adjust the refractive outcome for an unsatisfied corneal reshaping patient. Moreover, small adjustments in the refractive outcome are possible with corneal reshaping that may not be possible with refractive surgery simply because of the inherent variability of the surgical procedure itself.

Central corneal scarring that develops post surgically can produce glare and create significant visual problems for patients. Orthokeratology is thought to only affect corneal epithelial thickness and upon discontinuation of the procedure the central corneal thickness returns to normal.

Dealing with complications. The complications experienced with orthokeratology are significantly less severe and frequent than those associated with refractive surgery. Those complications that do arise are completely reversible simply by discontinuing lens wear.

Besides not having to worry about irreversible results and complications, orthokeratology requires less from those considering undergoing the procedure.

Minimal restrictions

Orthokeratology in children as young as eight years is approved and because myopia at this age is still developmental, the effects are more proactive as a mechanism to reduce a patient's overall nearsightedness.

In comparison, refractive surgery patients must be 18 years of age or older and demonstrate refractive stability for at least one year, so the procedure is reactive to myopia progression. There has been no indication that refractive surgery slows the progression of myopia even after the procedure.

The government approves

When the FDA officially approved corneal refractive therapy in June 2002, it stated, "The results of the data provided from this [The FDA's] clinical study revealed no major complications or slit lamp findings and four adverse events, which resolved. Additionally, the results show that 90% of the eyes completing the study achieved visual acuity of 20/40 or better at nine months and 99% demonstrated a reduction in pretreatment myopia.

The FDA concludes that the results of this study are consistent with GP lenses when worn for extended wear and that the benefits of these lenses are greater than the risk that may be associated with wearing GP lenses overnight."

Weighing the options

As an alternative to refractive surgery, orthokeratology has significant advantages including improved corneal shape, reversibil ity and adjustability, avoidance of central corneal tissue involvement and lack of significant complications. Plus patients don't entertain a fear of surgery.

Overall, orthokeratology offers significantly fewer risks and potentially the same reward when compared to refractive surgical procedures.

 

Orthokeratology Research Round Up

Here's more proof of the benefits of this procedure.

  • Several studies (Stone, 1976; Perrigin, et. al., 1990; and Khoo, et. al., 1999) have shown that rigid lenses on average slow the progression of myopia in children by approximately 50%. Most probably, in addition to epithelial thinning, rigid lenses have been shown to slow axial elongation in children that helps reduce myopia (Grosvenor, et. al. 1989; Khoo, et. al. 1999).
  • A pilot study, the Lenses for Overnight Orthokeratology Study (LOOK), Rah, 1999, has demonstrated excellent clinical efficacy to corneal molding with 74% of subjects achieving 20/20 uncorrected vision in the morning and safety as demonstrated by 90% to 95% of the 60 patients with staining showing less than grade 2 corneal staining.
  • The Children's Overnight Orthokeratology Investigation (COOKI), Walline (in progress) pilot study demonstrated excellent efficacy for corneal reshaping in 29 children with an average uncorrected visual acuity of better than 20/25, which was achieved after just two weeks of lens wear. Safety, as measured by corneal staining, was 56% of the subjects and less than that found in the LOOK study.
 

 

Dr. Lebow operates a private practice specializing in contact lenses, clinical research and consultation to the industry. He's a member of the American Optometric Association and a Fellow of the American Academy of Optometry.

 



Optometric Management, Issue: May 2003