Refractive error is the inability of the eye to accurately focus rays of light coming from a distance on the retina. It is a refractive surgery that adjusts the eye to view the image properly, which depends entirely upon the state of the eye.
It is a non-surgical treatment that gently reshapes your cornea during the night using a therapeutic lens, which results in the temporary correction of near-sightedness (with or without moderate astigmatism). The CRT lenses are similar in appearance to standard contact lenses. In most cases, they are removed upon waking, allowing freedom from glasses and contact lenses during the day.
The surgical correction of refractive errors of the eye is a subfield of ophthalmology called refractive surgery. In recent years, this subfield has become increasingly specialized. Ophthalmologists now have a variety of refractive surgical methods at their disposal for the individualized correction of refractive errors. Today, there are refractive surgery techniques for the cornea and lens that reliably meet the standard criteria of safety, efficacy, cost-effectiveness, and predictability of the refractive outcome.
An excimer ("excited dimer") laser has a wavelength of 193 nanometers and operates with argon fluoride. By using laser ablation, the cornea is remodelled so that light rays falling upon the eye will point precisely at the place on the retina with the sharpest vision (macula). The procedures employing excimer lasers to correct refractive errors are of two types:
Surface treatment techniques
Lamellar treatment techniques.
The surface treatment techniques include photorefractive keratectomy (PRK), laser-subepithelial keratomileusis (LASEK), and epi-LASIK. In these three types of procedure, corneal tissue is ablated with an excimer laser just below the corneal epithelium, which is the outermost of the five layers of the cornea. Before ablation, the corneal epithelium is removed by a mechanical or chemical method or with a laser (as in PRK), with an alcohol solution (as in LASEK), or else it is separated from the underlying tissue with a microkeratome (as in epi-LASIK). After ablation, the corneal epithelium is put back in place.
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