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LASIK
Eye Surgery Information to help the
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Laser refractive surgery has gone through an evolution beginning in the early 1990s with PRK. PRK uses an excimer laser was fired directly through the Bowman's layer and into the stromal layer of the cornea to reshape its curvature effecting the refraction of the patient. PRK tended to be very uncomfortable because of the eye's wound response. Discomfort continues until the epithelium grew back over the ablated area. Newer techniques limit patient discomfort, but rarely eliminate discomfort completely.
Additionally, because of corneal haze due to wound response, the safe refractive change with PRK was limited to approximately + 3 D to -6 D correction. Newer techniques have expanded that range, but corneal haze is still an issue that needs to be accommodated.
Lasik was the next evolution in laser refractive surgery. Lasik involves a precise incision into the stromal layer of the cornea, creating a flap. The flap is lifted exposing the stroma, where the excimer laser ablates the tissue, reshaping the curvature from within. Lasik effectively fools the cornea into not knowing that it has surgery, so the procedure is virtually painless and given the control of the depth of flap, Lasik has the ability to correct a much wider range of correction (+5D to -15D). While Lasik solved many of the issues surrounding PRK and widened the range of correction, it has its own set of complications and refractive issues. The majority of the complications relate to the flap itself and the optical aberrations, which are attributed to it.
Ever in search of a better procedure, ophthalmology returned to
surface ablation solutions, primarily LASEK. The primary methodology
around this procedure was to attempt to separate the epithelial
layer from the top of the cornea, ablate the underlying tissue with
the excimer laser and replace the epithelium on top of the cornea
making it act as a biological bandage contact lens. This greatly
reduced the pain seen in PRK and eliminated the flap-related issues
plaguing Lasik. Although LASEK reportedly improved patient comfort
and reduced the probability of corneal haze, the alcohol solution
required to release the epithelial cells from the underlying cornea
mortally wounds all cells, delaying vision recovery and creating an
unstable epithelial layer until the cells are replaced.
Epi-Lasik attempts to provide the best of both Lasik and PRK/LASEK.
By using a blunt blade to lift the epithelium in a single sheet, the
epithelium is a much more viable entity. The repositioned epithelium
acts as a bandage while the underlying cornea heals. Although
current studies are inconclusive if patient outcomes are better with
Epi-Lasik when compared to PRK or LASEK, many studies have shown
that the surface ablation class of Epi-Lasik, LASEK, and PRK
provides better outcomes than Lasik and All-Laser Lasik.
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Epi-Lasik
uses a blunt microkeratome blade to lift the epithelium in one sheet
of cells.
