How Common is Myopia?
Myopia is becoming more prevalent - some might even say it has become an epidemic. Myopia (nearsightedness) has increased in the US population by 66% in the last 30 years. The World Health Organization has categorized myopia with cataract, macular degeneration, infectious disease and vitamin A deficiency as among the leading causes of blindness and vision impairment in the world. Myopia is divided into two groups - low and high. The low group is up to -6.00 diopters in correction and the high (or pathological) group is greater than -6.00. The pathological group has a much higher incidence of potentially blinding conditions including macular degeneration, retinal detachment, glaucoma, loss of visual acuity and color sensitivity. The prevalence of myopia varies by ethnic group reaching as high as 70-90% in Singapore. In Japan it is estimated that over a million people suffer from a vision impairment associated with high myopia that cannot be adequately corrected with glasses or contact lenses. The prevalence of pathological myopia in some population based studies is as high as 3% of the population. In addition to the visually disabling effects are the economic costs - not only for the treatment costs but also for the loss of income due to visual disability. Since no universally accepted treatments have been able to reverse the structural changes of pathological myopia (the lengthening of the eyeball and thinning of the retina) it has long been the goal of research scientists in vision and ophthalmologists and optometrists to understand the factors that lead to these devastating changes in the structure of the eyeball and to devise therapeutic strategies. The common solution of wearing glasses or contact lenses is temporary as most children will get worse each year, resulting in more blur and thicker and heavier lenses.
Although most researchers agree that there is a genetic component to the development of myopia there is a growing amount of research implicating visual experiences early in life that affect eyeball growth and the subsequent development of myopia. Studies with animals (chickens, tree shrews and others) show that early visual experience affects the growth of the eye and the eventual myopia that may result. Specifically, the mismatch between the focus of central and peripheral vision can induce myopia. A typical eyeglass or contact lens that gives sharp central focus will overcorrect the peripheral focus. This causes myopia to increase. Some medications have a biochemical effect that will slow down the progression of myopia, but they typically have undesirable side effects. The newest research shows that specially designed bifocal contact lenses can slow down or even stop the progression of myopia. The most exciting studies show that orthokeratology can stop and even reverse (during the treatment period) the myopia that has already occurred, but only up to a certain amount, typically -6.00 diopters.
What Can We Do about Myopia?
Orthokeratology is vision correction without surgery. Orthokeratology, is also known as corneal refractive therapy (CRT), vision shaping treatment (VST), corneal molding or Ortho-K. It is the gentle reshaping of the cornea to correct myopia (nearsightedness). The cornea is the eye's equivalent of a watch crystal. It is a clear, dome shaped structure that overlies the colored iris. Its tissue is very thin (about 1/50th of an inch) and very pliable. Because the cornea separates the eye from air and because it has a curvature that bends light towards the back of the eye, it is responsible for 2/3rd of the eye's corrective power and contributes to various conditions such as nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. We can compensate for the eye's focus defects by reshaping the cornea.
It has been practiced for over 40 years. In the early years a series of lenses were fit on the eye, each with a progressively flatter fit, with the goal of reshaping the curvature of the eye. The techniques and success have greatly improved over the last 10 years. Now orthokeratology is accomplished by using specially designed contact lenses called reverse geometry lenses that gently flatten the cornea by pushing the central epithelial layers directly over the pupil towards the periphery of the cornea. This movement of corneal cells causes the center of the cornea to be thinner and flatter thus focusing the light closer to the retina. Orthokeratology refocuses the images on the retina in the same way as LASIK, but reversibly. Orthokeratology is FDA approved and FDA certified training is required of eye doctors to fit overnight ortho-K lenses. Only a handful of orthokeratology lenses have been approved for overnight orthokeratology by the FDA. A commonly used approved lens is the Paragon CRT (Corneal Refractive Therapy) Lens.
Corneal Molding has evolved into a method where many patients achieve success with the first lens. Good results typically take less than a week. The process is accomplished while you sleep using a computer designed reverse geometry contact lens. The lenses are inserted at bedtime and removed in the morning. The lenses, also known as vision retainers, safely and gently reshape the cornea changing the eye's focus. Most patients will have good vision throughout the day. Some patients may only need to wear their lenses on two or three nights a week to maintain good vision. Ortho-K can produce results in a surprisingly short period of time. The length of treatment to achieve your goals can vary from patient to patient. Factors which can affect the speed of treatment include your initial degree of myopia, the rigidity of your cornea, the exact topography (shape) of your cornea, your tear quality and your expectations. Children are especially good candidates because their corneas are more pliable and because any intervention at an early age will benefit them for the rest of their lives.
Patients interested in orthokeratology start with an eye exam and a free orthokeratology screening. After a comprehensive eye exam, including an orthokeratology consultation, corneal topography is done. These are topographical maps of the cornea. Everyone's topographical map is different, much like our fingerprints. Corneal topography shows irregularities in the cornea and is essential to designing contact lenses that will mold your cornea. Corneal topography also allows us to diagnose corneal diseases such as keratoconus. Specular microscopy is also performed which allows us to see that the endothelial corneal cells are healthy and fulfilling their function of keeping the cornea from becoming waterlogged and from losing its transparency.
Research also shows that the amount of time that children spend outdoors in the daylight also slows down the progression of myopia. There is still much for us to learn in combating nearsightedness, but we now have the tools to at least make a significant impact in controlling myopia.
Dr. David Littlefield
www.littlefieldoptometry.com
Dr. David Littlefield is a 4th generation optometrist and a 2nd generation orthokeratologist. He practices in Leawood, Ks in the Kansas City metro area. He has had experience in slowing down and even reversing myopia with bifocal contact lenses and with orthokeratology lenses. He also believes that nutrition and exposure to outdoor daylight are beneficial influences.
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