Orthokeratology
	About Myopia Myopia (nearsightedness) has been labeled as one of the most common ocular disorders affecting human beings—and is increasing worldwide. The increased incidence is occurring worldwide as countries industrialize and education levels rise. The percentage varies from country to country from as little as 25% in the United States to as much as 90% in some parts of China . This has caused concern among some governments and their health agencies with regard to the ability of citizens to function in times of emergency and natural disasters. This concern has sparked an interest in a variety of methods to attempt to control or reduce myopia including: Contact lens fitting methods (orthokeratology) to temporarily reduce myopic correction requirements-an FDA approved technique. Surgical techniques (RK, PRK, LASIK, etc.) to permanently alter the corneal shape, reducing myopic correction requirements History Orthokeratology is the temporary reduction of myopia achieved by the programmed application of contact lenses to reshape the cornea. Modern orthokeratology achieves this using specially designed reverse geometry gas permeable (GP) ortho-k shaping lenses worn during sleep.This overnight wearing process provides a faster, more predictable result than early ortho-k attempts as practiced in the 1960s using conventional, rigid contact lenses fitted incrementally flatter. Modern 4-, 5-, and 6-zone designs speed corneal reshaping and the myopic reduction process while the wearer sleeps. Using this technique, properly selected patients can go through the day wearing no correction and usually enjoy excellent visual acuity. Orthokeratology, or ortho-k fitting, has been employed since the early 1960s in one form or another in the United States. George Jessen first attempted to deliberately change refractive myopic error using rigid contact lenses using a technique he named “Orthofocus.”  • Orthokeratology has been used in some form since the 1960s in the USA. • Early ortho-k fitting was time consuming and expensive, with unpredictable results. • Early reverse geometry ortho-k shaping lens designs made myopic reduction more predictable and achievable. The reasons for failures of earlier designs were due to lack of appropriate corneal mapping Topography devices, use of PMMA lenses, which were not adequate for overnight wear.  For more than two decades, orthokeratology did not gain widespread acceptance, partly due to resistance from the scientific community who maintained that altering the central cornea would not be safe. Optometry and ophthalmology did not accept the procedure as being sound in the absence of clinical evidence that this procedure would not interfere with the structure and function of the cornea. The fact that only keratometry was available to evaluate, demonstrate, and monitor corneal topographical changes limited its use to a body of fitters who had ample anecdotal evidence, yet little scientific data. For this reason, orthokeratology was classified as a “fringe” science at best. The introduction of corneal mapping instruments allowed a more scientific approach to employing this procedure. Studies were carried out using standard PMMA lens designs to test the theory. These studies showed a certain reduction in myopia during treatment before a “plateau effect” limited further myopic reduction. These reductions in myopia varied from 0.30 to 1.52D in subjects with 2.50 to 4.00D of myopia. The time it took to achieve these changes ranged anywhere from three to ten months, with varied myopia reduction rates reported among individual patients during the treatment time. On average, most myopia reduction occurred during the first six months. The problems with these early methods were that the amount of myopia reduction was difficult to predict and visual acuity often fluctuated greatly during the course of the treatment. Predicting ortho-k success using the early fitting methods was dependent on the initial shape of the cornea even though the method of determining this was based on an inherently inaccurate corneal measurement system (keratometry). Myopia reduction did not last very long when lenses were worn occasionally on a daily wear basis. The lack of high-permeability GP materials did not allow for safe overnight wear of a retainer lens to maintain corneal shape. CORNEAL TOPOGRAPHY MACHINE USED FOR FITTING OF ORTHO K LENSES MODERN ORTHOKERATOLOGY Theory/Mechanisms The new orthokeratology designs have allowed the reshaping process to take place rather quickly. This accelerated form of ortho-k (also known as AOK) offers some immediate change after one-night wear of the shaping lens, with the remainder usually occurring over a treatment period of about 10–30 days. There is debate regarding the actual mechanism by which orthokeratology works. Some believe that the rigid shaping lenses actually bend the cornea to reshape it and thereby reduce myopia. Other studies seem to indicate that the corneal shape changes in orthokeratology are temporary, demonstrating that the cornea is elastic and has a “memory” (the cornea will resume its pre-ortho-k shape, once lens wear has been discontinued). This is contrasted to a “plastic” change (one where the cornea is permanently molded into a different shape by wear of a rigid lens). Polse’s result in this study showed that whatever the mechanism, the changes to the shape of the cornea and resultant myopic reduction were temporary and reversed themselves once rigid contact lens wear was discontinued. The question remained whether this was due to a bending of the corneal surface or by another mechanism.Newer studies suggest that ortho-k shaping lens fitting using reverse geometry GP designs may compress corneal tissue (in some fashion) rather than changing refractive error by bending the cornea, at least after initial adaptation. The hypothesis is that a thin layer of tear film exists between the back of the ortho-k shaping lens and the central cornea. These tear film “shear” forces act hydraulically to force a compression and possibly subsequent redistribution of very anterior epithelial cells under the shaper from the center toward the periphery. It must be remembered that the reduction of myopia, whether done permanently by means of removing tissue by use of a laser (LASIK and PRK) or by changing corneal shape by use of ortho-k shaping lenses, is measured in microns or thousandths of a millimeter. For example, the cornea is estimated to be approximately 540 microns in thickness or about 0.54 millimeter (Figure 1 ).                     Figure 1 Corneal thickness by layer Note that these lenses shape only the epithelium layer (in pink). The epithelium is only 50 microns in thickness i.e. the thickness of a human hair. The amount of compression force of a contact lens to induce change in this epithelium is minimal, yet it brings about a change in power comparable to surgical procedures like LASIK. Moreover the change is reversible. So, the gradual redistribution of corneal mass in orthokeratology that takes place under the shaping lens is what accounts for the reduction in the sagittal depth and thickness of the cornea, and the resultant reduction in myopia. The advent of new high-permeability GP materials (ISO/Fatt Dk of 85 or more) has allowed overnight wear of these ortho-k shaping lenses instead of during the day.* This provides easy and fast lens adaptation for the patient. New innovative four, five, and six curve reverse geometry designs in large diameters have not only allowed for better control of position of the shaping lens, but have also provided ortho-k fitters with a scientific and more accurate means to control and predict myopic reduction. These modern ortho-k shaping lenses allow for rapid myopia reduction as well. What took nine to twelve months to achieve in the ’60s now will occur usually within 30 days. Approximately 70 to 80% of the patients treated with modern ortho-k shaping lenses achieve their desired myopia reduction with only one pair of shapers, as compared to the old process that often took eight or more pairs of conventional rigid contact lenses to achieve myopia reduction. The first approvals for overnight orthokeratology in the U.S. were obtained by Paragon Vision Sciences (CRT®) and Euclid Systems Inc. (Emerald Lens). Orthokeratology Candidate Profile • Age: juvenile to adult myopes • Spherical refractive error: -1.00 D to -6.50 D spherical power correction • Cylindrical refractive error: - 1.50 D or less “with-the-rule” corneal astigmatism - 0.75 D or less “against-the-rule” astigmatism • Recreational and sports activities where periods without wearing visual correction are beneficial • Those whose vocation requires unaided visual acuity for certain periods, such as police, firemen, military, or occupations where refractive surgery may be a cause for exclusion (deep-sea divers, high altitude pilots, etc.) • Free of corneal dystrophies (e.g. keratoconus), ocular diseases, or any condition that may preclude the patient from wearing any type of GP lens • Motivated to undergo full or partial myopia reduction and willing to return to the office for two to three months of active treatment and every six months for passive treatment • Committed to the initial and ongoing cost of ortho-k treatment Risk Analysis There is a small risk involved when any contact lens is worn. It is not expected that the Shaping lens will provide a risk that is greater than other overnight wear rigid gas permeable contact lenses. The most common patient symptoms concerned poor distance vision and flare/ghosting (visual disturbances). The incidence of these symptoms tends to decrease over time in orthokeratology treatment, and they will go away if lens wear is discontinued. The two most common side effects, which occur in general contact lens wearers, are corneal edema and corneal staining. It is anticipated that these two side effects will also occur in some wearers of Orthokeratology Shaping Lenses. Other side effects, which sometimes occur in all hard lens wearers, are pain, redness, tearing, irritation, discharge, or abrasion of the eye. These are usually temporary conditions if the contact lenses are removed promptly and professional care is obtained. When overnight orthokeratology shaping lenses dislocate during sleep, transient distorted vision may occur the following morning after removal of the lenses. This distortion may not be immediately corrected with spectacle lenses. The duration of the distorted vision would rarely be greater than the duration of the daily visual improvement normally achieved with the lenses. In rare instances, there may occur permanent corneal scarring, and resulting permanent decreases in vision may occur. In addition, studies have shown that smoking increases the risk of corneal ulcers, for those who wear lenses overnight. You should remove your lenses if any abnormal signs are present. Maintaining Effects of Orthokeratology Shaping Lenses for Overnight Orthokeratology The long-term wear of Orthokeratology Shaping Lenses Treatment, does not eliminate the need to continue wearing shaping lenses to produce the reduction in myopia. After the cornea has been changed by wearing these shaping lenses, you must continue overnight wear of the lenses to maintain the results. Usually the treatment lenses will continue to be the lenses worn after successful treatment. In cases of low pretreatment myopia, the effect may last for more than one day. Note: To maintain the Shaping Treatment effect of myopia reduction, overnight lens wear must be continued on a prescribed schedule. Failure to do so can affect daily activities (e.g., night driving), visual fluctuations and changes in intended correction. Ortho-k Shaping Lens Care and Handling In order to minimize the potential for wearing complications such as eye irritations or serious infections, patients must be thoroughly trained in the proper way to wear and care for their ortho-k shaping lenses, and using good hygienic methods whenever they handle their ortho-k shapers. Preparing the Lens for Wearing Cleanliness is a very important aspect of proper care of the shaping lenses. Hands should be clean and free of any foreign substances whenever the shaping lenses are handled. • Always wash, rinse, and dry hands thoroughly before handling the shaping lenses. • Avoid soaps containing cold cream, lotions, or oily cosmetics prior to handling shapers. These substances can adhere to the surface of the shaping lens and be difficult to remove. • Handle shaping lenses with the fingertips, avoiding use of fingernails that can scratch or chip them. • Always start with the same shaping lens first to avoid mix-ups. • Remove the shaping lens from its storage case and examine it. Be sure it is clean, moist, and free of any nicks or cracks. Placing the Lens on the Eye After thoroughly washing and rinsing hands, follow these steps to insert the shaping lens on the eye: • Remove shaping lens from case. • Rinse shaping lens with fresh conditioning solution. • Inspect shaping lens for cleanliness, uniform wetness, and unwanted debris. • Rub several drops of fresh conditioning solution over the surface of the shaping lens. • Place shaper on the top of index finger of dominant hand. • Hold down lower lid and lift upper lid up with other hand. • Gently place shaping lens on the center of the eye. It is not necessary to press the shaper on the eye. • Gently release lids and blink. The shaping lens should center automatically. • Use the same technique to insert the other lens. • The wearer should be instructed to place two or three drops of the recommended rewetting solution in each eye prior to wear. Removing the Shaping Lenses Before attempting to remove a shaping lens, it is very important that the wearer verify that it is moving. If the shaping lens is not moving, instill 5 drops of the recommended rewetting solution. Oftentimes an adhered lens will begin to move spontaneously after instillation of drops and a few minutes of blinking. Wait until the shaper begins to move freely with the blink before attempting to remove it. While looking upwards, a finger is placed at the lower eyelid margin at the edge of the shaper to gently but firmly apply pressure. Looking downward, the process is repeated using the fingertip placed on the upper eyelid at the shaper edge. The patient should then look straight ahead and blink several times. Once the shaping lens begins to move, it can be removed using one of the following methods: The shaping lens may be removed manually by using the “blink” or “scissor” method customary with standard GP lenses. Cleaning and Storing the Shaping Lenses The shaping lenses should be rubbed gently for 20 seconds on each side with the recommended cleaner, followed by a thorough rinse in the recommended solution. Care must be taken not to press or squeeze the shapers excessively during handling. Ortho-k shaping lenses are susceptible to distortion and breakage. The cleaned shaping lenses should be placed in the proper well of the case and covered completely with the storage (conditioning) solution. Maintaining the proper orthokeratology effect depends on the patient wearing the prescribed shaping lens on the correct eye. Laboratories manufacturing ortho-k lenses produce them in different colors between right and left to help the patient avoid a mixup. The ortho-k shaping lenses should be allowed to soak for a minimum of four hours or as recommended on solution label. If a multi purpose solution (such as Boston Simplus) is used, all steps (including protein removal) are performed with the one solution only.  KEY POINT SUMMARY… • The combination of modern reverse geometry designs, high Dk GP materials, and corneal topographers make orthokeratology fitting fast, safe, and more predictable. • One of the most critical visits for both the patient and the practitioner is the first morning after the shaping lenses are worn at night. • An advantage of orthokeratology is that it is reversible. • Pre-fitting examination does not vary much from those routine exams done in the office. • It has been suggested that patients who may expect the best chance for success with ortho-k treatment are those candidates who have steep corneas with high eccentricity,