4 Myths of Orthokeratology: Fiction and Fact

4 Myths of Orthokeratology Fiction and Fact

This is the first installment in a series on orthokeratology (ortho-k). The goal is to dispel some of the myths surrounding it as a vision correction technique. Part two will cover some of the obstacles ortho-k needs to overcome to get itself to the next level in the US market. And finally, part three highlights some the “tips and tricks” that take your ortho-k practice to the next level.

From its inception, orthokeratology has always been a “fringe” area of optometry. That is partly due to the fact that it is still relatively young. The modality did not exist its current form until the early 2000’s when the Paragon CRT system gained FDA approval. The concept of ortho-k existed before that, but like many innovations in our modern world, it came into existence purely by accident. Doctors in the 1960s that fit very flat GP lenses noticed that patients claimed their uncorrected vision after removing the lenses was much better than their uncorrected vision prior to application. This was was due to the flattening effect caused by the flat base curve of the lens which in turn corrected some of their myopia. It took those 40 years of trial and error by a small number of people to create the ortho-k industry we think of today.

The relative infancy and spontaneity of its development have both helped and hindered ortho-k as a treatment. Though popular in Asia, it remains largely unknown to patients in North America. If you mentioned it as an option, the next question would likely be, “What is ortho-k?” Because the market is quite small, ortho-k has is covered relatively superficially in the modern optometric curriculum. It’s no surprise that misinformation and myths have developed as a result. Let’s set the record straight on some of the big ones.

Myth One: Ortho-k lens physically compress corneal tissue

The first thing most people, patients and doctors alike, misunderstand about ortho-k is how it works. It’s true that ortho-k lenses are simply gas permeable corneal lenses with a base curve that is flatter than keratometric value of the cornea. The lenses take advantage of reverse geometry designs. The degree to which the lens is flatter is directly related to the amount of myopia one wishes to correct. If a 1.00 D myope has a flat k of 43.00 D, flattening the cornea to a value 42.00 D reduces the refractive power and coincidentally corrects the myopia.

The point that is misunderstood is how that flattening takes place. Many think that the contact lenses physically press on the corneal epithelium and “squish” them or cause cells from the center to migrate to the periphery. Both are incorrect. Ortho-k treatment is achieved as a result of hydraulic forces beneath the contact lenses. A properly fit ortho-k lens forms a semi-closed fluid/tear reservoir inside the alignment zone of the lens.

orthokeratology lens anatomy
Anatomy of an ortho-k lens

At the apex of the cornea, the fluid reservoir thickness is between 5-10 microns. In the periphery, under the reverse curve of the lens, the reservoir thickness is between 30 and 60 microns. As a result, the corneal epithelium at the apex are dehydrated, losing their cytoplasm, and become thin. Corneal epithelium under the reverse curve of the lens take in fluid, increasing the volume of cytoplasm, and become thicker. Essentially, the corneal epithelium are altered to mimic the shape of a minus powered soft contact lens. You do that by using fluid pressure gradients to influence cell hydration, not by mechanically compressing the tissue.

orthokeratology tissue changes
Tissue changes due to hydraulic forces

Interestingly, changes in thickness of the corneal epithelium required to flatten the corneal curvature and provide treatment are relatively low. The average treatment zone size of an ortho-k lens is approximately 3.0 mm. Using the Munnerlyn formula (Treatment Zone Diameter2 X Refractive Error/3 = change in tissue thickness), we find that a 3.0 micron change is all that is needed to correct a -1.00 D myope. That is only a 5% change for a cornea with an epithelial thickness of 55 microns. Not a giant feat, even if we are only using pressure gradients to manipulate tissue. If we are talking about making changes that are on the order of microns (remember, a red blood cell is 5.0 microns wide), how in the world are we going to be precise enough fitting a contact lens to provide an accurate treatment? That brings us to our second myth.

Myth two: Ortho-k fitting is too complicated

It is true, ortho-k fitting in the past was a little complicated. We simply didn’t have tools to precisely measure the corneal surface and manufacture lenses to fit it. Even if we had, our knowledge of what is critical to a successful ortho-k fit was limited. Fortunately, today’s industry is at a point where the success rate with the first lens is quite good (usually 75% or higher). It just depends on which fitting method(s) you choose take advantage of.

Empirical Fitting

This is likely the easiest, most user friendly way to fit ortho-k lenses. Some lens designs simply require K’s, Spec Rx, and HVID measurements. Other systems will require other additional data given by your corneal topographer, but the advantage is that you don’t have to worry about putting lenses on and taking them off on the first visit, or doing any extra work up testing. You may need to simply add one or two components (HVID measurement) to your standard exam, and you could order a set of custom lenses for any patient that walks through the door. This type of fitting tends to be the easiest but also gives you the least control over the lens design. If you don’t nail it on the first try, it can be difficult to troubleshoot issues moving forward.

orthokeratology empirical fitting
Empirically fit lens from K’s, Rx, and HVID

Diagnostic Fitting

Some systems are based on a diagnostic fitting with a fit set. The advantage of having a fit set is that you are able to see the lens on eye and make adjustments instantly. You develop your troubleshooting skills more quickly because you are able to see the differences in fit in real time. You also don’t have to wait days or weeks for new lenses to come in. You can simply dispense a lens out of your fitting set the same day the patient comes in for consult/fitting, then re-order a replacement. That’s a huge advantage when you’re going for the “wow” factor of ortho-k.

Custom Design

There are a number of different tools available to practitioners who want to design their own lenses. While you do have to have a deeper understand of what is going on with the lens in order to custom design them, the software does a significant portion of the work for you (provided the measurement data you provide is accurate—more on this in part 3). The two major advantages to this system are that you are in full control of the lens design and can make any change you would like to any lens parameter. Unfortunately, it’s a blessing and a curse because there is more than one way to fix a low riding lens. You just have to have enough experience to know which way is best. That develops over time. Custom designed ortho-k lenses probably have the steepest learning curve of all the lens designs. However, the other advantage of customizing ortho-k lenses is cost. Proprietary lens designs are marked up significantly. So if you structure your fitting fees to include cost of lenses, custom lenses (often seen as a generic reverse curve lens by the manufacturing laboratory) can cost half as much as proprietary designs.

Bottom line: Ortho-K fitting/design can be as simple or complicated as you choose to make it.

Myth three: Ortho-k is risky

For a lot practitioners, safety of ortho-k is their biggest hang up. The thought of putting a lens on a child and sending them to bed is scary. That is understandable. We’ve had it drilled into us that sleeping in lenses of any kind is dangerous. However, very few adverse events have been the result of ortho-k wear throughout its relatively short history.

Infection

Rates of microbial keratitis have been reported to be approximately 7.7 cases per 10,000 patient years.1 In other words, if you had 100 patients in lenses, you would see, on average, one case every 13 years. Additionally, most of the adverse cases reported resulted from improper care of lenses, including exposure to tap water. When compared with other contact lens modalities, rates of microbial keratitis in ortho-k wearers are similar to those of overnight soft lens wear.2 So if you have any patients on an overnight soft lens wear schedule, they are just as likely to have adverse event as any ortho-k patients you fit.

Hyopixa

Another sticking point for some folks is oxygen transmissibility. Fortunately, this has become a non-factor as a result of an increase in materials with Dk values at or above 100. While there is a slight increase in mid peripheral corneal swelling (2% to 6%) when the lenses are first worn overnight, overall corneal swelling is similar to that of non-lens wearing eyes after 30 days of use.3 Most proprietary lens designs are in high Dk materials by default. But it’s worth investigating before you begin fitting lenses. If you plan on custom designing lenses, make sure to specify the material they are manufactured in.

Long term corneal changes

At this point, we as industry have a good handle on the short term (<1 year) effects of ortho-k, but simply don’t have large amounts of data on those patients wearing ortho-k lenses for >10 years. Some anecdotal evidence shows that, provided a lens is fit properly, there are no detrimental changes, such as permanent corneal warpage, in patients wearing lenses for over a decade. A handful of patients have come through our clinic after wearing ortho-k lenses for 10 to 15 years wanting the be refit. The recovery process took 2 to 6 week and everyone was correctable to 20/20 with no adverse corneal changes. Interestingly, the amount of time it took to recover calls into question the assumption that ortho-k is an epithelial phenomenon. The entire corneal epithelium regenerates in 7-10 days.4 If it were only the epithelium that changed after orth-k wear, the cornea should completely return to its pretreatment shape after those 7-10 days. A possible explanation for this discrepancy in recovery time may be due to changes to bowman’s and the central stroma. There is evidence that both of these layers due change during ortho k wear and their effects can persist long after lens wear has been discontinued. One study even suggests the changes to Bowman’s may be irreversible.5 That said, none of the changes caused a reduction in vision and refractive error does stabilize.

Bottom Line: Provided the patient’s lenses fit properly and they care for them properly, ortho-k is very safe vision correction modality.

Myth Four: Ortho-k is a waste of chair time

This is actually true…. If you don’t invest the time and resources upfront to implement a system to fit the lenses effectively. An average ortho-k fit can take up to six visits (consult, dispense, 1 day, 1 week, 1 month, 6 month), but many of these can be scheduled for 15 minute slots if done correctly. Just like any other specialty you choose to offer, you have to do some work up front to ensure it goes smoothly.

Know what you’re talking about

In the United States, most of the population has never heard of ortho-k. Naturally, it will be on you (and your staff) to educate patients on the benefits, risks, etc. An explanation of the ortho-k should be as natural as an explanation of cataracts. Highlights should include myopia controlling effects (though modality is not technically FDA approved for myopia control so be careful with advertising) and convenience. Nailing your scripts will make the flow during the consult and fitting process much consistent schedule friendly.

Educate your staff

The two edged sword of ortho-k (and most contact lenses in general) is that the success or failure the specialty is often dependent on the staff. The evaluation of a lens on eye or a topography is a very quick process. It is the education, application and removal training, and initial work up that consumes the majority of the visit. So if 90% of the visit is the hands of your staff, your focus should be on developing their skills. They should be just as knowledgeable on the information concerning myopia, how the lenses work, and (especially) care of the lenses. If done correctly, you should be the enforcer of the information presented by the staff, not the primary source.

Conclusions

From the outside looking in, ortho-k can look like a side wise or strange technique. I know because I used to think so. I believed all of these myths at one time or another. It wasn’t until I had the opportunity to fit a number of different ortho-k lens designs that I was convinced of ortho-k’s efficacy as a whole. Now, I have some skin in the game and wear ortho k lenses myself.

That said, there are a number of big hurdles the ortho-k industry must overcome to gain market share. Fortunately, there are things we can do to get it to the next level. That’s the topic of next section in this series on ortho-k. Orthokeratology Part 2: Obstacles. The final section will provide you with some specific and actionable ways to get more comfortable fitting lenses and building your ortho-k practice.

References

References

  1. Bullimore MA, Sinnott LT, Jones-Jordan LA. The risk of microbial keratitis with overnight corneal reshaping lenses. Optom Vis Sci 2013;90:937–44.
  2. Liu YM, Xie P. The Safety of Orthokeratology–A Systematic Review. Eye Contact Lens 2016;42:35–42.
  3. Alharbi A, La Hood D, Swarbrick HA. Overnight orthokeratology lens wear can inhibit the central stromal edema response. Invest Ophthalmol Vis Sci 2005;46:2334–40.
  4. Remington LA. Chapter 2 – Cornea and Sclera. In: Clinical Anatomy and Physiology of the Visual System. Vol ; 2012:10–39.
  5. Nieto-Bona A, González-Mesa A, Nieto-Bona MP, Villa-Collar C, Lorente-Velázquez A. Long-term changes in corneal morphology induced by overnight orthokeratology. Curr Eye Res 2011;36:895–904.

About Steven Turpin

Steven Turpin
Cornea and Contact Lens resident at Pacific University. My interests include practice management and specialty contact lens care. I am fascinated with the use of multifocal soft lenses for myopia control.Currently researching all things specialty contact lens related.

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