Is Orthokeratology OK In the New Millennium?
BY EDWARD S. BENNETT, OD, MSED
Practically on a daily basis, practitioners ask about the status and viability of orthokeratology. Likewise, manufacturers are quite interested in knowing whether they should be pursuing orthokeratology designs. Clinical studies are being performed pertaining to the effect of RGP lenses, both on the progression of myopia in young people and on established myopes in their late teens and older. The million dollar question appears to be: If refractive surgery is "slash for cash," is ortho-k "mold for gold?" I've surveyed several of the leading orthokeratologists for their opinions.
What is the status of ortho-k in the United States?
At this time the Contex OK lens is the only FDA-approved lens. There are several other designs which have initiated the FDA process for approval. It would not be unrealistic to expect approval of these designs by 2001, with some approvals possible this year. Most of the recent interest pertains to overnight wear, in which the patient wears a high Dk RGP lens every night until the desired endpoint has been reached and then moves to an every other night, every third night, or similar schedule for retainer wear. There are 10 to 15 nightwear designs in about four to five different materials at the current time.
According to the FDA, doctors can use currently approved products in an off-label capacity for the patient's benefit, provided doctors can confirm their ability to design the lenses. Any practitioner promoting orthokeratology should read the advertising guidelines that have been established by the National Eye Research Foundation (www.nerf. org) and reviewed by the FTC. These guidelines provide information to help practitioners minimize the risk of violating FTC guidelines.
The ability to wear these lenses overnight only, and be able to promote them accordingly, will allow consumers who are not interested in refractive surgery to have a reasonable opportunity to have visual freedom during the day while wearing contact lenses solely as a retainer at night.
What happens to the cornea during ortho-k?
This answer is currently under debate. According to a recent publication by Swarbrick Wong and O'Leary, the large changes in corneal curvature may result from a redistribution of corneal tissue at the anterior surface rather than overall bending of the cornea. The central cornea thins (primarily epithelial) accompanied by midperipheral corneal thickening (primarily stromal).
How much myopia reduction can occur with ortho-k?
There is much individual variability as to the amount of myopia reduction. The amount of reduction can often vary between 1.00D to 4.00D, although higher amounts of reduction are possible in some individuals. According to Mountford, greater myopia reduction occurs with higher cor-neal eccentricity (e-value), steeper corneal curvatures and larger horizontal visible iris diameters. In fact, he has proposed the following reduction in corneal eccentricity to achieve a certain amount of myopia reduction:
1D = .26e; 2D = .42e; 3D = .58e;
4D = .74e; 5D = .90e.
In my next column (June 2000), I'll discuss fitting the current generation of orthokeratology contact lenses, as well as what the future may hold for this new segment of contact lens fitting and practice.
Acknowledgements: I'd like to thank Drs. Cary Herzberg, John Rinehart, Roger Tabb and John Mountford for their contributions to this column.
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and executive director of the RGP Lens Institute.