LASEK

Photorefractive keratectomy
Intervention
Photorefractive keratectomy at U.S. Naval Medical Center San Diego.
ICD-9-CM	11
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Photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (or laser epithelial keratomileusis) (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.

Up to 80% of the myopic population may physically qualify for PRK. There are a number of basic criteria which a person should satisfy:

There are also some pre-existing conditions that may complicate or preclude the treatment.

Some complications that can be temporary or permanent include:

As with other forms of refractive surgery, , colloquially referred to as 'dry eye,' is the most common complication of PRK, and can be permanent. In more advanced cases, recurrent erosions occur during sleeping from adherence of the corneal epithelium to the upper eyelid with rapid eye movement. Adjuvant polyunsaturated fatty acids (PUFAs) with high Omega-3 content before and after surgery improves sicca, possibly due to their anti-inflammatory effects. Foods containing PUFAs include flax and fish oil. Brush PRK to denude the epithelium, instead of alcohol based techniques, also result in quantitatively lower ocular dryness after surgery. The amount of corneal hazing after surgery is also decreased with brush technique. The platelet activating factor LAU-0901 has shown effect in mitigating dry eye in mouse models. Rabbit models have also shown improvement with topical nerve growth factor (NGF) in combination with docosahexaenoic acid (DHA).Mitomycin C worsens post-surgical dry eye.