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Photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (or laser epithelial keratomileusis〔("Laser epithelial keratomileusis (LASEK)" ) Accessed June 30, 2008.〕) (LASEK) are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses. LASEK and PRK permanently change the shape of the anterior central cornea using an excimer laser to ablate (remove by vaporization) 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 microtome, will remain that way permanently with only limited healing or remodelling. With PRK, the corneal epithelium is removed and discarded, allowing the cells to regenerate after the surgery. The procedure is distinct from LASIK (laser-assisted in-situ keratomileusis), a form of laser eye surgery where a permanent flap is created in the deeper layers of the cornea. ==Eligibility== Up to 80% of the myopic population may physically qualify for PRK. There are a number of basic criteria which a person should satisfy: * Normal ocular health * Age 18 years or older * Stable refraction error (no noticeable change in the last year) correctable to 20/40 or better * Between −1.00 to −12.00 diopters of Myopia * Not pregnant at the time of surgery * Realistic expectations of the final results (with a complete understanding of the benefits, as well as the possible risks) * Pupil size 6 mm or less in a dark room is ideal (but some newer lasers may be acceptable for larger pupils) * Assessment of allergies, (e.g., pollen) where allergy may complicate the eyelid margins following surgery leading to dry eye. There are also some pre-existing conditions that may complicate or preclude the treatment. * Collagen vascular disease (e.g., corneal ulceration or melting) * Ocular disease (e.g., dry eye, keratoconus, glaucoma) * Systemic disorders (e.g., diabetes, rheumatoid arthritis) * History of side effects from steroids *Granular corneal dystrophy type II 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (or laser epithelial keratomileusis("Laser epithelial keratomileusis (LASEK)" ) Accessed June 30, 2008.) (LASEK) are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses. LASEK and PRK permanently change the shape of the anterior central cornea using an excimer laser to ablate (remove by vaporization) 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 microtome, will remain that way permanently with only limited healing or remodelling. With PRK, the corneal epithelium is removed and discarded, allowing the cells to regenerate after the surgery. The procedure is distinct from LASIK (laser-assisted in-situ keratomileusis), a form of laser eye surgery where a permanent flap is created in the deeper layers of the cornea.==Eligibility==Up to 80% of the myopic population may physically qualify for PRK. There are a number of basic criteria which a person should satisfy:* Normal ocular health* Age 18 years or older* Stable refraction error (no noticeable change in the last year) correctable to 20/40 or better* Between −1.00 to −12.00 diopters of Myopia* Not pregnant at the time of surgery* Realistic expectations of the final results (with a complete understanding of the benefits, as well as the possible risks)* Pupil size 6 mm or less in a dark room is ideal (but some newer lasers may be acceptable for larger pupils)* Assessment of allergies, (e.g., pollen) where allergy may complicate the eyelid margins following surgery leading to dry eye.There are also some pre-existing conditions that may complicate or preclude the treatment.* Collagen vascular disease (e.g., corneal ulceration or melting)* Ocular disease (e.g., dry eye, keratoconus, glaucoma)* Systemic disorders (e.g., diabetes, rheumatoid arthritis)* History of side effects from steroids*Granular corneal dystrophy type II」の詳細全文を読む スポンサード リンク
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