Normally, the rays of light entering the eye are brought to a precise focus on the retina – the light sensitive layer lining the back of the eye. When such a focus is not achieved, a refractive error results and vision is not clear. These imperfections in the focusing power of the eye are called refractive errors.
A myopic eye is longer than normal or has a cornea that is too steep, as a result of which the light rays focus in front of the retina. Close objects look clear, but distant objects appear blurred.
Hyperopia is a term used to describe the condition of farsightedness. The causes of hyperopia are typically genetic and involve an eye that is too short or a cornea that is too flat, as a result of which images focus at a point behind the Retina. People with hyperopia can usually see distant objects well, but have trouble focusing on nearby objects.
ASTIGMATISM (cylindrical error) occurs when the incoming light rays are unable to reach a common focus within the eye. Astigmatism distorts or blurs vision for both near and far objects. The cornea is the clear front window of the eye. A normal cornea is round and smooth, like a basketball. When you have astigmatism, the cornea curves more in one direction than in the other, like a football. It is possible to have astigmatism in combination with myopia or hyperopia.
Glasses are time proven and have been in existence for a thousand years. They are affordable (unless you buy multiple pairs of designer frames), easy to maintain, and versatile. They may, however, restrict peripheral vision, be difficult to wear in certain weather conditions, cause magnification of images, cause a number of visual aberrations (including halos around lights), and have a limited usage life. They may interfere with certain occupations and recreational activities, and some people don’t like the impact glasses have on their appearance.
Contact lenses are another common solution for the correction of refractive visual problems. Advantages include more natural vision, no change in cosmetic appearance, improved visibility, more freedom in recreational activities, and better peripheral vision. On the other hand, contacts are high maintenance, may get lost, are less comfortable for patients with dry eyes, may cause visual aberrations (including halos and fluctuating vision), and always carry an increased risk of infection and possible corneal scarring. In higher altitudes many adults become intolerant of contact lenses over time because of dry climate and decreased oxygen in the air.
There are so many types of contact lenses available today – soft, rigid, gas permeable, toric for astigmatism, etc. – to suit people with nearsightedness, farsightedness, or astigmatism, For people who are presbyopic and over thirty-five, contact lenses can be fit asymmetrically to obtain monovison for reading. Ophthalmologist and optometrists recommend not sleeping with any contact lens in because this increases the chance of corneal infection.
Refractive Surgical Procedures:
Refractive surgical procedure intended to reduce a person’s dependency on glasses or contact lenses. The most common refractive surgical procedures performed today are:
LASIK (Laser In-Situ Keratomileusis):
It is a surgical procedure intended to reduce a person’s dependency on glasses or contact lenses. In this procedure a thin hinged flap of cornea (the cornea is the transparent, dome-shaped window covering the front of the eye) is created and lifted to one side in order to allow laser treatment to the deeper part of the cornea. The flap is then repositioned in its original position.
EpiLASIK ( Epithelial Laser-Assisted In-Situ Keratomileusis: EPI LASIK) – it is a procedure, which combines the advantages of PRK and LASIK, Epi lasik involves the use of a microkeratome, similar to LASIK, however only the superficial epithelial layer of cornea is separated as in PRK and this flap is replaced following the reshaping of the cornea using the Excimer Laser.
PRK ( Photorefractive Keratectomy ), which was the original kind and is still sometimes used. It involves gently scraping some surface cells off the cornea and then using a laser beam to re-shape it.
Refractive Surgery (LASIK) Procedure:
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