However, since contact lenses are worn directly on the eyes, they require proper evaluation and care to safeguard eye health. Ortho-k or CRT. Another option for treating myopia is orthokeratology ortho-k , also known as corneal refractive therapy CRT. In this nonsurgical procedure, you wear a series of specially designed rigid contact lenses to gradually reshape the curvature of your cornea, the front outer surface of the eye. The lenses place pressure on the cornea to flatten it.
This changes how light entering the eye is focused. You wear the contact lenses for limited periods, such as overnight, and then remove them. People with mild myopia may be able to temporarily obtain clear vision for most of their daily activities. Laser procedures. Laser procedures such as LASIK laser in situ keratomileusis or PRK photorefractive keratectomy are also possible treatment options for myopia in adults.
A laser beam of light reshapes the cornea by removing a small amount of corneal tissue. In PRK, a laser removes a thin layer of tissue from the surface of the cornea in order to change its shape and refocus light entering the eye. LASIK removes tissue from the inner layers, but not from the surface, of the cornea. To do this, a section of the outer corneal surface is lifted and folded back to expose the inner tissue. A laser then removes the precise amount of corneal tissue needed to reshape the eye.
Then, the flap of outer tissue is placed back in position to heal. Other refractive surgery procedures. People who are highly nearsighted or whose corneas are too thin for laser procedures may be able to have their myopia surgically corrected. A doctor may be able to implant small lenses with the desired optical correction in their eyes. The implant can be placed just in front of the natural lens phakic intraocular lens implant , or the implant can replace the natural lens clear lens extraction with intraocular lens implantation.
This clear lens extraction procedure is similar to cataract surgery but occurs before a cataract is present. Vision therapy for people with stress-related myopia. Vision therapy is an option for people whose blurred distance vision is caused by a spasm of the muscles that control eye focusing. Vision tests and eye examinations determine the prescription for your lenses just as they do for glasses, and the contact lenses correct your vision in the same way, by changing the direction in which light enters the eye.
The lenses can be vastly thinner than eyeglass lenses because of their proximity to the cornea. There are different types of contact lenses:. Both eyeglasses and contact lenses correct your vision on a daily, temporary basis. For permanent correction of myopia, you will want to consider refractive surgery, which changes the eye permanently and usually requires no daily correction afterward. Options include:. Patient Login Referring Doctors. The image distance is negative, because it is on the same side of the spectacle as the object.
The negative power indicates a diverging or concave lens, as expected. The spectacle produces a case 3 image closer to the eye, where the person can see it. If you examine eyeglasses for nearsighted people, you will find the lenses are thinnest in the center. Additionally, if you examine a prescription for eyeglasses for nearsighted people, you will find that the prescribed power is negative and given in units of diopters.
Since the farsighted eye under converges light rays, the correction for farsightedness is to place a converging spectacle lens in front of the eye. This increases the power of an eye that is too weak.
Another way of thinking about this is that a converging spectacle lens produces a case 2 image, which is farther from the eye than the object see Figure 3.
Then the image produced by a spectacle lens must be at this distance or farther for the farsighted person to be able to see it clearly. Figure 3. Correction of farsightedness uses a converging lens that compensates for the under convergence by the eye. The converging lens produces an image farther from the eye than the object, so that the farsighted person can see it clearly.
What power of spectacle lens is needed to allow a farsighted person, whose near point is 1. When an object is held An image 1. The object is The positive power indicates a converging convex lens, as expected. The convex spectacle produces a case 2 image farther from the eye, where the person can see it. If you examine eyeglasses of farsighted people, you will find the lenses to be thickest in the center. In addition, a prescription of eyeglasses for farsighted people has a prescribed power that is positive.
Figure 4. This chart can detect astigmatism, unevenness in the focus of the eye. Check each of your eyes separately by looking at the center cross without spectacles if you wear them.
If lines along some axes appear darker or clearer than others, you have an astigmatism. Another common vision defect is astigmatism , an unevenness or asymmetry in the focus of the eye. For example, rays passing through a vertical region of the eye may focus closer than rays passing through a horizontal region, resulting in the image appearing elongated.
This is mostly due to irregularities in the shape of the cornea but can also be due to lens irregularities or unevenness in the retina. Because of these irregularities, different parts of the lens system produce images at different locations. The eye-brain system can compensate for some of these irregularities, but they generally manifest themselves as less distinct vision or sharper images along certain axes. Figure 4 shows a chart used to detect astigmatism. Astigmatism can be at least partially corrected with a spectacle having the opposite irregularity of the eye.
If an eyeglass prescription has a cylindrical correction, it is there to correct astigmatism. The normal corrections for short- or farsightedness are spherical corrections, uniform along all axes.
These lenses are thinner and lighter than regular plastic lenses, making them more attractive and comfortable. Also, anti-reflective coating is highly recommended for lenses that correct nearsightedness. AR coating eliminates distracting reflections in the lenses, making them appear thinner and more attractive. Eliminating reflections also improves vision and comfort.
Ortho-k contact lenses are another choice for the correction of nearsightedness. These are specially designed rigid gas permeable GP contact lenses that not only correct existing myopia — they may actually help control myopia progression in children. Finally, people with moderate to severe myopia may benefit from implantable lenses.
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