Photorefractive keratectomy

Photorefractive keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (LASEK) are laser eye surgery procedures intended to correct a person's vision and reduce his dependency on glasses or contact lenses. The first LASEK procedure was performed at Massachusetts Eye and Ear Infirmary in 1996 by ophthalmologist, refractive surgeon, Dimitri Azar.[1] The procedure was later popularized by Camellin, who coined the term LASEK for laser epithelial keratomileusis. LASEK and PRK permanently change the shape of the anterior central cornea using an excimer laser to ablate (burn off) a small amount of tissue from the corneal stroma at the front of the eye, just under the corneal epithelium. The outer layer of the cornea is removed prior to the ablation. A computer system tracks the patient's eye position 60 to 4,000 times per second, depending on the brand of laser used, redirecting laser pulses for precise placement. Most modern lasers will automatically center on the patient's visual axis and will pause if the eye moves out of range and then resume ablating at that point after the patient's eye is re-centered.

The outer layer of the cornea, or epithelium, is a soft, rapidly regrowing layer in contact with the tear film that can completely replace itself from limbal stem cells within a few days with no loss of clarity. The deeper layers of the cornea, as opposed to the outer epithelium, are laid down early in life and have very limited regenerative capacity. The deeper layers, if reshaped by a laser or cut by a microkeratome, will remain that way permanently with only limited healing or remodelling. In LASEK the corneal epithelium is preserved with a chemical solution, peeled off, and replaced after the laser ablation is complete. In PRK the epithelium removed is discarded and allowed to regenerate. Both procedures are distinct from LASIK (Laser-Assisted in-SItu Keratomileusis), a form of laser eye surgery where the epithelium is not removed.

Photorefractive keratectomy

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