point - TOPIC: The Future of Orthokeratology

Ortho-k Provides Many Benefits to Patients and Practitioners

BY JOHN MARK JACKSON, OD, MS, FAAO

Irecently had a great clinic day. I had four long-term orthokeratology patients in for their annual exams on the same day. Each of them had been doing overnight ortho-k for at least five years; had uncorrected acuity of 20/20 or better in each eye; and had corneas that were free of neovascularization, staining, visible edema, clouding, scarring, or any other clinical evidence that they weren't using "normal" contact lenses. None had ever had an infection related to ortho-k. Some of them were able to wear their lenses every other night and maintain good vision the second day.

And all of them, when I asked if they intended to continue with ortho-k or return to "normal" contact lens wear, expressed surprise that I would even suggest discontinuing ortho-k.

A sample size of four patients isn't much, but it generally represents how my ortho-k patients do with the procedure and how they feel about it. A recent study by Hiraoka (2009) as well as earlier studies such as one by Lipson (2005) show a high satisfaction rate with ortho-k correction compared to daily wear soft lenses.

Easier Than Ever

Early ortho-k had a number of issues that made the modality cumbersome. Lenses were worn during the day; it took multiple lenses and months to get full correction; it was difficult to hit the refractive target; and only about –1.00D on average could be corrected (Polse 1983).

Modern reverse geometry (RG) lenses have solved these problems. High-Dk materials make overnight lens wear possible, making ortho-k wear more convenient for patients. Precision manufacturing and the RG lens configuration make it easier to correct higher amounts of myopia with one or two lenses. Results from a study by Tahan (2003) show that most designs are equally able to treat refractive error, and in this study the average treatment was about –2.50D (which reflected the average pre-treatment error).

With the development of toric peripheral systems, larger amounts of astigmatism are now correctable, though we are still learning about their efficacy.

Professionally Fulfilling

Ortho-k can be a refreshing change of pace from routine soft lens fits. Ortho-k fitting is not easy, but it's not especially complex, either. Because ortho-k lenses are different from standard GPs, they really require a deeper understanding of how sagittal depth and other lens parameters affect the fitting characteristics. Learning to fit ortho-k lenses and going through the certification process required for each design will give you a much better understanding of GP lenses in general. Your understanding of corneal topography maps will also improve as you learn to interpret topographical changes caused by the lenses.

Patients get excited about the ortho-k process, and it is great to watch as their acuity improves and they become less dependent on daytime vision correction over the course of several weeks. And, if you make sure to charge appropriately for your services, it can serve as a welcome addition of income to the practice.

Not for Everyone

Ortho-k is not for every low myope out there. It doesn't always result in the desired refractive outcome, and it does increase higher-order aberrations. It takes at least a week or two to achieve full correction.

Most notably, there have been high-profile cases of microbial keratitis that should give all practitioners pause. But what we lack is good data on how ortho-k compares to other lens types in terms of infection risk. Studies are underway to determine this and should give clinicians more information to make an educated decision on the relative clinical safety of this modality. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #167.

Dr. Jackson is an associate professor at Southern College of Optometry where he works in the Cornea and Contact Lens Service, teaches courses in contact lenses, and performs clinical research.

counterpoint - TOPIC: The Future of Orthokeratology

Orthokeratology: Proceed With Caution

BY DANIELLE M. ROBERTSON, OD, PHD, FAAO, FBCLA

Orthokeratology offers a fully reversible means of refractive correction, rendering patients free of contact lenses or spectacles for daytime wear. In recent years interest has surged in the use of ortho-k to slow or inhibit myopia progression, with preliminary reports on the use of this modality suggesting a potential role in slowing axial elongation rates (Walline et al, 2009).

As the target population for this type of lens wear is children, which would mandate extensive lens wear over time, it is imperative that the effects of ortho-k on the biology of the cornea as well as safety profiles are established.

Corneal Epithelial Compression, Biology, and Visual Function

Like other refractive procedures, the basic science explaining the effects of ortho-k on the biology of the cornea lags behind clinical application. At the cellular level, overnight ortho-k lens wear results in significant thinning of the corneal epithelium underneath the area of lens compression, thereby altering the apical corneal curvature (Alharbi and Swarbrick, 2003). While this reduces refractive error and improves uncorrected visual acuity, the overall quality of vision may be affected. Increased higher-order aberrations and glare along with reduced contrast sensitivity persist throughout the treatment period (Kobayashi et al, 2008).

Further, it remains to be established whether the significant thinning in the epithelium compromises the integrity of the tight epithelial barrier or disrupts normal renewal mechanisms. Animal studies of ortho-k lens wear have suggested alterations in the rate of cell division within the basal layer of the epithelium (Matsubara et al, 2004). As basal cells within the corneal epithelium are limited in the number of times they can divide, sustained cell division in the central cornea would require an influx of cells from the limbus. This raises a new concern for long-term ortho-k lens wear and the longevity of the critical limbal stem cell population.

Also, the tear film, which provides nutritional support to the epithelium and tight barrier as well as contributes to antimicrobial defenses, is altered after overnight ortho-k (Choy et al, 2004); however, more studies are needed to investigate these effects.

Safety First

In stark contrast to GP lenses fit on alignment — the lens modality that remains the frontrunner for posing the lowest risk for corneal infection — an alarming increase in the number of contact lens-related microbial infections has been reported following overnight ortho-k. Specifically, both Pseudomonas and Acanthamoeba have been identified as the primary causative agents in ortho-k-related corneal infection (Sun et al, 2006). The majority of these infections have been reported in children and are predominantly confined within specific Asian populations (Watt and Swarbrick, 2007). This geographic distribution likely reflects the high numbers of patients within these areas electing to undergo ortho-k lens wear and may be due in part to inadequate lens care practices, including the use of tap water (Robertson et al, 2007).

Overnight lens wear remains the leading risk factor for lens-related microbial keratitis (Stapleton et al, 2008). Even in a hyper-Dk/t lens material, the compressive effects of the ortho-k lens on the corneal epithelium potentially render the cornea susceptible to an increased risk of infection. To date, the necessary clinical and laboratory-based studies to effectively evaluate the effect of ortho-k lens wear at the cellular level are non-existent.

Until the overall safety profile is established, it is imperative that patients are fully educated about the potential risks associated with ortho-k lens wear along with the importance of proper hygiene and compliance prior to initiating lens fitting. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #167.

Dr. Robertson is a corneal epithelial cell biologist and an assistant professor of Ophthalmology at the University of Texas Southwestern Medical Center at Dallas.