Corneal Refractive Therapy (CRT)
What is Orthokeratology/Corneal Refractive Therapy (CRT)?
Orthokeratology (Ortho-K) is a vision correction therapy for patients with moderate myopia (nearsightedness) and low amounts of astigmatism. A retainer, worn at night, manipulates the fluid forces of the tear layer in your eye to reshape your eye's outer surface. (By tear layer, we mean, of course, the layer of clear salty lubricating liquid in your eye, the same liquid that is in tear drops when one cries.) A "contact lens" retainer while you sleep.
Modern Orthokeratology (Ortho-K) is a vision correction therapy for patients with moderate myopia (nearsightedness) and low amounts of astigmatism. It involves wearing a contact lens retainer while you sleep to gently and painlessly reshape the surface of your eye. By controlling the shape change of your epithelium (outer layer of your cornea) we alter the refractive power of your eye to correct the error in your vision. While you sleep, the tiny forces applied by your tears squeezed between your retainer and cornea apply the necessary tension to reshape the surface of your eye.
TheOrtho-K retainer never actually touches the cornea; it sits on a layer of your natural tears. In addition, the forces applied to your epithelium are so minute, it is impossible to feel or sense the effect of the lenses on your eye. But you will see the effects of the therapy when you remove the Ortho-K retainer in the morning. Your myopia has been corrected and you enjoy your day without glasses or contacts! Its reversible and non-surgical
The reversible nature and long term effects of Ortho-K therapy can be understood by comparing it to wearing a ring on your finger. When you remove a ring, the skin has been moulded. The longer you wear that ring, the longer it takes for the skin to return to its normal shape. Ortho-K therapy affects the cornea in a similar nature. After a month of nightly wear, your eye will have an increased retention of the correcting effect. In other words, the cornea holds its altered shape for a longer period. This reduces the number of nights that you are required to wear your retainers.
After a year of therapy, many patients wear their Ortho-K retainers only 1 or 2 nights per week! Wearing Ortho-K retainers only a limited number of times per week, and only while asleep, makes the therapy very attractive to patients looking for an alternative to glasses and conventional contact lenses. The therapy also provides you with the piece of mind that its effect is reversible should you choose to discontinue wearing your Ortho-K retainers. Because it is non-surgical, you can return to your pre-therapy vision and corneal shape by simply not wearing your Ortho-K lenses.Orthokeratology offers many distinct and unique benefits. But clearly, the reasons to choose Ortho-K therapy is for the freedom it offers you from glasses & daily contacts and the sharp vision that results. How does it Work?While sleeping, an Ortho-K retainer, via fluid pressure, gently reshapes the "lens" of your eye improving its focussing power. When you waken and remove the retainer your eye retains this improved shape throughout the day, delivering natural unassisted 20/20 vision.
You can reverse the effects by ceasing to wear the retainer, and your eye will gradually return to its natural shape. What is wrong with my vision?A nearsighted (myopic) patient has little difficulty with near vision but a reduced ability to see in the distance. If light rays entering the eye (through the cornea) are incorrectly focused on the retina then a patient will have blurred vision (worse than 20/20). Imagine the retina as a movie screen, and the cornea as the lens of a projector and everything that we see as the light source. If the lens of the projector is not accurately focused, the image on the screen is blurred. However, if we change the focusing power of the projector lens, we can improve the quality of the image on the screen. Ortho-K fixes the problem.
Orthokeratology improves the focusing power of the lens. By changing the refractive power of the eye, we can accurately focus light rays on the retina providing crisp, clear vision. In fact, very small shape changes in the cornea can improve a patients' vision dramatically. The part of the cornea most affected by Ortho-K is the epithelium or outer "skin" of the eye. The epithelium is made up of layers of cells which behave in a very fluid-like nature. In fact, the epithelium is 400 times more sensitive to pressure than the surface below (the stroma).
Ortho-K manipulates the fluid nature of the epithelium to change the focusing power of the eye. By "pulling" central cells towards the periphery of the cornea, a "flattening" effect is created which improves the patients' ability to see in the distance. What exactly happens? Moving cells is easily understood. You can press your thumb into your leg and see the skin move. If you hold your thumb there long enough, you will see the impression in your skin. The magic of Ortho-K is controlling the shifting of epithelial cells to achieve the required refractive change.
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