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Review of Corneal Reshaping: Orthokeratology
2 CPD in Australia | TBA in New Zealand | 27 February 2017
By Ken KoppThrough all of the new developments and technology in the contact lens industry during the last fifty years, the art and science of reshaping has benefited greatly. It has become more advanced and successful, allowing much faster and greater vision improvements.
Broken down into its Greek origins, ‘orthokeratology’ can be translated as “the science of straight corneas.” A more useful, modern definition would describe orthokeratology (orthoK) or corneal reshaping as a non-surgical contact lens treatment used to temporarily reduce or eliminate myopia and moderate amounts of astigmatism.
OrthoK used to refer to “a series of increasingly flatter lenses” intended to achieve the desired results. Today’s reshaping products can often satisfy those requirements with a single lens in the majority of cases.
The History of Orthokeratology
During the1950s, spherical rigid lenses made of polymethylmethacrylate (PMMA) were fitted to thousands of patients around the world.
These lenses were often fit one to two dioptres flatter than the flattest central keratometer reading with the intention of ensuring a flow of oxygenated tears across the cornea and to flush away any trapped debris.
Some patients, however, weren't able to tolerate their lenses for all or most of their waking hours. Additionally, some patients experienced a noticeable blurring of vision after removing their contact lenses and switching to their eyeglasses. Newton Wesley, O.D., (a founder of the Wesley-Jessen Contact Lens Company and the National Eye Research Foundation) established the term “spectacle blur” to describe this phenomenon.
In many situations involving spectacle blur, the observation of corneal oedema, was accompanied by a flattening of the central cornea.
These patients were the first recipients of “unintentional” orthoK.
A number of astute practitioners theorised that if the cornea could be “unintentionally” reshaped, perhaps it could also be intentionally reshaped, but in a controlled manner. They were correct, and their work led to the development of modern orthokeratology.
These pioneering practitioners, among many others, included optometrists Charles May, Stuart Grant, Newton Wesley, George Jessen, Sanford Ziff, Ned Paige, Donald Harris, Richard Wlodyga, Joseph Nolan, Alfred Fontana, Ron Kearns, Roger Tabb, Roger Freeman, Jerome Garber and Robert Buffington.
In the beginning of the 1960s, these and other practitioners developed their unique techniques for fitting orthoK. In 1962, George Jessen, O.D., (a former student of Dr. Wesley) termed his approach “orthofocus”.1 For many years, the method of orthoK most widely used was the May-Grant method, named after Charles May, O.D., and Stuart Grant, O.D. This method used relatively large, flat lenses with large Optic Zone Diameters (OZDs). For example, a May-Grant lens might be 10.0mm in overall diameter with an OZD of 8.4 to 8.6mm. A series of lenses were needed, each lens successively flattening the cornea in small increments until the desired results were attained, which may take months to years to accomplish.
Along the way, in the mid-sixties, the International Orthokeratology Society was established, which helped to spread the practice of orthoK worldwide.
Then in 1971, Leonard Seidner, O.D., and polymer chemist Norman Gaylord, were instrumental in developing Polycon, the first silicone acrylate rigid gas permeable (GP) lens material, which had a Dk value of 7. The silicone added to the PMMA polymer allowed more oxygen to easily pass through the material, reducing hypoxic stress and increasing wearing times. Gas permeable lenses revolutionised the contact lens industry, and spurned the development of greater and greater permeability in newer materials. These materials were far more physiologically compatible with the cornea's oxygen requirements and the practice of orthoK benefited greatly.
Also, due to enhanced permeability, larger diameter lenses could be used. Larger lenses enhanced centration and provided better corneal reshaping results.
The next major advancement in orthoK came in 1989. Richard Wlodyga, O.D., working in conjunction with contact lens laboratory veteran Nick Stoyan, developed Accelerated Orthokeratology (AOK). Wlodyga’s theory was that corneal changes could be induced much quicker than standard orthoK if the posterior secondary curve could be made steeper than the base curve.
He believed that a steeper secondary curve would enable the steepening of the mid-peripheral cornea to be less impeded and to occur more rapidly than in standard spherical designs. The accelerated method was revolutionary. OrthoK could now be completed in a fraction of the time and the concept of accelerated orthoK with the use of reverse geometry lenses (RGL) was successfully introduced.
Others followed his lead and designed their own RGL for orthoK treatment. Reverse geometry ushered in the second generation of orthoK.
AOK / RGL Designs
AOK was made possible by the development of RGL designs. RGL not only accelerated treatment but provided the capability for systemised approaches and more predictable results.
The standard RGL had three distinct zones, which can be manipulated to achieve an optimal fit.
Unlike a standard multi-curve lens design where the centre is steep and, progressively flattens toward the periphery, a RGL design is the opposite and requires reverse thinking. The base curve is flatter than the flattest central K measurement by an amount that is variable, and dependent on the individual patient's flat K reading and refractive error. The secondary ‘reverse’ curve is steeper and ‘returns’ the lens design to the peripheral cornea. The outer alignment zone of the lens parallels the peripheral cornea, which helps maintain centration and proper alignment of the lens (Figure 1).
The most important factor for a successful fit is good lens centration. The optic zone diameter is typically smaller than that used for standard multi-curve lens designs and generally between 6.0mm and 6.5mm for most RGL designs. Using smaller OZDs than this can induce unequal curvature changes in the visual axis. These changes can cause blurring, ghost images and flare. The back surface curvature of the treatment zone is the base curve.
If the lens does not centre properly, ghost images and flare may be induced. If the lens is decentred, the out-of-alignment flattening of the cornea can lead to induced astigmatism and irregular corneal topography.
In order to safely produce the maximum reduction of myopia and astigmatism, the flattest possible lens that centres well is desired. Sufficient lens movement of 1mm to 2mm in the open eye is also important to prevent lens adhesion while asleep.
The secondary reverse curve allows a tear reservoir and returns the lens to the cornea in the mid-periphery. The cornea’s epithelial tissue in this area is engorged from fluids from the compressed central and peripheral cells to this area of relief and allows the oblate shape of the cornea to take place. The steepness of this secondary curve also provides centration of the lens, which is critical for success. This secondary reverse curve can vary in size and depth from one design to another. The alignment curve controls the lens movement and positioning and parallels the peripheral cornea. Together, the secondary reverse curve and the alignment curve provide centration and proper alignment of the lens to the cornea. They control how the treatment is applied. This zone may be spherical, aspheric or, in some designs, have a cone angle, which is a straight line set at an angle tangent to the portion of the cornea it touches. Subtle changes in this zone can significantly impact the contact lens centration and ultimately treatment results.
The overall diameter is the distance from lens edge to edge and is generally between 10mm to11mm in size. Larger diameter lenses can enhance centration; an important factor in this treatment.
Excessively flat or steep corneas, may not respond as well to this treatment.
The shape value or eccentricity value of the cornea describes the change in curvature between the central and peripheral parts of the cornea. This value may be determined by using a corneal topographer or peripheral K readings. A cornea is described as having a positive shape value if the central cornea is steeper than the peripheral cornea. A negative shape value is assessed when the central cornea is flatter than the peripheral cornea. In addition, a zero shape value describes a spherical shape in which the central and peripheral curves are equal.
Corneas with a positive shape value respond best to reshaping. There is definitely a learning curve to this process for contact lens professionals. When new to the corneal reshaping process, it is recommended that the first five to ten patients fitted are in the moderate myopia range (under -4.00D of myopia with up to -1.00D of astigmatism).
Patients who have been long term gas permeable lens wearers or are current reshaping lens wearers will be much more difficult to fit. Corneas can be difficult to reshape after a GP lens has been worn for a relatively long period because the cornea has already undergone some corneal changes. Corneal rigidity is one of the most important variables in determining how much ametropia may be reduced. The fitter should be aware of the role that corneal rigidity plays in contributing to success or failure. It is assumed that the less rigid the cornea, the greater the magnitude of ametropia reduced and the retention of the results achieved.
21st Century of Corneal Reshaping
OrthoK, AOK, or Corneal Refractive Therapy (CRT); regardless of the terminology used, it describes a non-surgical, reversible, therapeutic procedure that uses specialized gas permeable lenses to gently reduce or increase the radius of curvature of the central cornea.
The lens design generates pressure in the thin layer of tears on the corneal surface and, in the mid-periphery, which is responsible for the change in the corneal shape. This action alters the curvature of the cornea and reduces or eliminates near sightedness, slight farsightedness (not FDA approved), and some astigmatism. The most recent development in this therapeutic treatment is to wear the contact lenses while sleeping and remove them upon waking. If therapy is discontinued for any reason, the cornea and vision return to the pre-treatment state so there is no permanent change in vision or corneal integrity.
This is an elective procedure for those who want an alternative to refractive surgery and do not want to wear glasses or contact lenses during daytime hours. If the patient does choose to discontinue the therapy at some point and opt for refractive surgery, the reversibility of the modality does allow it. The candidates, as well as the eye care professional providing this treatment, must be motivated and patient. There are limits to how much myopia and astigmatism can be effectively reduced. Patients who have mild to moderate amounts of myopia and some astigmatism are good candidates for this treatment, providing they are in good general and ocular health.
The materials used for these specialised contact lenses are of oxygen permeable polymers with Dk values now exceeding 100 making possible the development of night therapy and maintaining corneal health. These lenses can create and maintain a new corneal curvature that will provide improved unaided visual acuity, without added risk. Manufacturers are using computerized state-of-the-art lathes that enable tolerances to the micron level, further revolutionizing the process. These new therapeutic contact lenses allow visual improvement in considerably less time, as when orthoK was first practiced.
Overnight Corneal Reshaping
As we know, orthoK has been around for many years. OrthoK was being practiced with a variety of lens brands and designs but were only approved for daily wear use. Paragon Vision Sciences’ CRT system received the first overnight approval by the FDA on 13 June 2002, for overnight corneal reshaping using its CRT lens design and their HDS 100 material (Dk 100). Since then, there have been several other overnight reshaping designs approved under the B+L Vision Shaping Treatment umbrella.
This procedure is designed for patients who desire to eliminate their dependence upon their eyeglasses or contact lenses with no adverse effects or permanent damage to the eye. Good candidates are those patients who want improved unaided acuity without any of the risks of surgery. Patients with lifestyles that make eyeglasses or contact lenses less than desirable are also good candidates. Many eye care professionals believe that patients who have low amounts of myopia, up to –4.00 dioptre, with astigmatism up to –1.00 dioptre, are ultimately the best candidates. Most patients with myopia fall into these categories, which means that millions of myopic patients are candidates for corneal reshaping. There are no age restrictions for this procedure, unlike refractive surgery, which makes it an excellent modality for children and adolescents who are myopic. Just as there are good candidates for reshaping, there are patients who are not good candidates for this procedure. For example, any patient who does not fall within the prescription range of this treatment should not be fit. Poor candidates also include patients with any eye disease, injury or abnormality that affects the cornea, conjunctiva or eyelid; those who have a severe insufficiency of tears, reduced corneal sensitivity or systemic disease that may affect the eye.
Expected Results and Benefits
It is very important the patient receiving this treatment understands that, even with the most precise eye measurements and the proper contact lenses, it is not always possible to predict precise results. Results depends on several factors including the patient’s pre-treatment myopic prescription and corneal curvature.
Improvement in "functional vision" should be presented as the goal of the therapy. Functional vision means different things to different people, so it's advisable to determine exactly what constitutes the patient’s goals and whether slightly less than '20/20 may be a perfectly acceptable result in exchange for the convenience of not having to wear glasses of contact lenses throughout the day.
The Initial Work-up
A comprehensive vision and ocular health examination is the first step. The patient's clinical data has to fall in the approved and suggested range for corneal refractive therapy and the patient’s lifestyle and needs should then be discussed to confirm them as a good candidate.
A thorough slit lamp exam of the eye and its adnexa should be performed.
A computerised corneal topographer maps the elevations, contour, and shape of the cornea. Topography is the preferred method of analysing the cornea shape and radii. An accurate pre-fitting map is essential for software-based designs and to compare the progress of the treatment
Finally, specific measurements are taken to individually design the lenses for each eye.
From Fitting to Dispensing
A number of different manufacturers provide diagnostic fitting set from for fitting patients with reshaping lenses.
Along with any diagnostic set, training of the basic principles of corneal reshaping should be provided as well as the specifics in the chosen lens design.
After the correct fit of the patient's contact lens has been confirmed, patients must be instructed on application, removal, handling and care of the lenses before beginning the treatment.
Most patients experience rapid improvement in vision during the first few days of treatment and often achieve 90 per cent of the vision changes within the first week, while full treatment typically occurs within two weeks. During this initial treatment phase, patient's may need a series of temporary soft lenses until the desired prescription is achieved.
If the patient has been fitted with a lens system that is approved for overnight wear, the patient should be seen the first morning after sleeping in the lenses (as early as possible). To determine proper centration and how much visual change has occurred.
If possible, instruct the patient to not remove the contact lenses upon waking, but leave them on for this first appointment.
The first follow-up should consist of a refraction over the contact lenses, visual acuity with the contact lenses, an evaluation of the lens fit with and without the use of fluorescein, visual acuity without the lenses in place, an assessment of the corneal integrity, keratometry measurements, and corneal topography. This will all help to determine whether the same lenses are continued or whether the fitting relationship should be modified. Patients may notice a slight difference in vision between morning, afternoon and evening on the first few days, but this difference usually lessens as the cornea develops its new shape over time. Each patient responds differently depending on the amount of pre-treatment refractive correction and K readings. Temporary daily disposable soft lenses may be dispensed to the patient until the necessary correction of the reshaping effect is achieved. Or the patient may wear his gas permeable reshaping lenses during the daytime. This method provides crisp vision, corrects for residual corneal astigmatism and does not require a separate contact lens modality. Usually this is only needed during the first few days of treatment. After the initial first night of wear, corneal reshaping patients should be seen at one week (from the starting date of the procedure), one month, three months, and six months. Patients should be instructed to bring their lenses with them for every follow-up visit in case the need to inspect them for deposit build-up or evaluate them in situ. It is recommended that the patient have an in-office Progent cleaning of the lenses at the six month visit to keep the lens surfaces free of deposits. The patients’ treatment and lens parameters will be re-evaluated at their annual exam. Most manufacturers recommend yearly lens replacements.
Managing Myopia Progression
The progression of myopia in children has been a concern for practitioners over the years.2 Several different modalities, or combinations thereof, have been attempted to slow or retard the progression of myopia in children between the ages of eight and 18. Studies have shown that there are techniques that can be affective between 45 to 80 per cent.3 The use of overnight orthoK lenses and custom made centre distance soft multifocals allow approximately a 40 to 50 per cent success rates of reducing the progression of myopia without harmful side effects. Pharmacological interventions such as low dose (0.10 per cent) Atropine, can achieve a higher success rate but the long term side effects are concerning to most practitioners.
The increase of myopia and the risk of later in life retinopathy has increased to epidemic proportions worldwide. More studies are needed to determine additional modalities or improve on current modalities to determine the corrective measures in slowing or preventing myopia from becoming the risk factor it is today.
|Ken Kopp, FCLSA is Director of Clinical and Professional Services, Paragon Vision Sciences. Mr. Kopp has lectured worldwide on the clinical aspects, modality differences, and modern manufacturing of all types of contact lenses. He has held the position of Director of Clinical and Professional Services at Paragon Vision Sciences in Mesa, AZ, for over twelve years and is responsible for all practitioner/distributor training for Paragon material products and the Paragon CRT Contact Lens.|
1. Jessen, George “Orthofocus Techniques” Contacto,
pp 200 July, 1962
2. Choo J & Holdon B The Prevention of Myopia With Contact Lenses Eye &CL 33(6) :371-372 , 2007
3. Cho P, Cheung SW “Retardation of Myopia in Orthokeratology” (ROMIO) Invest Ophthalmol Vis Sci 2012; 53: 70077-85
OrthoK used to refer to ‘a series of increasingly flatter lenses’ intended to achieve the desired results