Excimer Photorefractive Keratectomy

What is myopia?

Myopia or short-sightedness is a condition in which the rays of light reaching the cornea (the clear front portion of the eye) are focused in front of the retina (the light sensitive portion of the eye). The resulting vision is thus, not clear and close objects are seen well than those at a distance.

How is Myopia Corrected?

Corrective Lenses: Contact lens and spectacles alter the path of the light rays to achieve precise retinal focus.

Surgical Options

Radial Keratotomy- 4 to 8 corneal incisions are made involving 95 to 99% of corneal thickness, to flatten the central cornea. Excimer laser photorefractive keratectomy (PRK) - removes 10-20% of the superficial corneal tissue, centrally. It thus weakens the cornea less than radial keratotomy.

The Excimer Laser

The word "Excimer" is a contraction of "excited" and "dimer". Dimer merely refers to the combination of atoms of argon and fluorine gases, to form an unstable molecule. When this unstable molecule breaks down, it emits photons of ultra-violet light, which are used in the laser. The excimer laser is a "cool" laser, which does not generate heat in the cornea. The laser photons destroy intermolecular bonds in the corneal tissue resulting in tissue removal by a process called photoablative decomposition. The absence of damage to the cells surrounding the ablated tissue renders this laser particularly suitable for delicate eye procedures. Removal of corneal tissue centrally flattens the corneal curvature. This alters the path of the light rays entering the eye, and allows precise retinal focusing in myopia. The laser is used to perform photorefractive keratectomy (PRK) for correction of myopia and phototherapeutic keratectomy (PTK) for removal of corneal scars. The Summit Excimer laser has been used to perform almost 50,000 PRK procedures till date, with extremely encouraging results.

The Treatment

Both PRK and PTK are performed on an outpatient basis with the use of topical anesthetic drops. You will thus, be awake during the procedure. A miotic drop is instilled in the eye to be treated, 30 minutes prior to the PRK procedure, to constrict the pupil. You will lie face up under the laser. The surgeon will key your refractive correction into the laser's computer. He will then ask you to fix your gaze on a target in the laser. The surgeon will then perform one or two familiarization sessions to help you get used to the laser target. He will then gently remove the thin outer layer of the cornea, called epithelium, after inserting a speculum to separate your lids.

He will activate the system to perform the corneal sculpting. This takes 15 to 30 seconds. The total time taken including positioning your eye under the laser is about 15 minutes. There is no pain during the procedure. The surgeon will then patch your eye. You should make arrangements for a relative or friend to take you home after the procedure, as no hospitalization is required.