الفهرس 
Anatomy of The CorneaOnly 14 pages are availabe for public view
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Abstract
The excimer laser has been used since the late 1980s to reshape the anterior corneal curvature in a procedure known as photorefractive keratectomy (PRK), initially for myopia and later for astigmatism and hyperopia. In this surgery, the epithelium is removed and the laser is applied to ablate a specific amount of Bowman’s membrane and stroma. The excimer laser can also be used to remove superficial corneal pathology in a procedure termed phototherapeutic keratectomy (PTK).
Corneal diseases such as scars, degenerations, dystrophies, bullous keratopathy, and band-shaped keratopathy (BSK) are important causes of visual blindness; anterior stromal disease being superficial can be treated using various minimally invasive surgical procedures like lamellar keratoplasty (LKP) or superficial keratectomy or by excimer lasers, that is, phototherapeutic keratectomy (PTK). PTK can be considered to be a bridge between medical and surgical management of corneal diseases.
PTK allows the removal of superficial corneal opacities and surface irregularities. It is similar to photorefractive keratectomy which is used for the treatment of refractive conditions.
Wound healing and re-epithelialization proceeds smoothly and shortly after the procedure with minimal tissue reorganization, this is in contrast to the incision made with diamond or steel blades that produce more irregular and diffuse tissue damage. Uses of PTK include treatment of corneal opacities resulting from the trauma (surgical and non-surgical), inflammations, dystrophies, and degeneration limited of the anterior corneal layers.
The procedure is generally done under topical anesthesia, unless some additional surgical procedure is combined with PTK (local anesthesia) or when the procedure is done in pediatric patients, general anesthesia may be required.
After debriding the epithelium, ablation is performed, In an eccentric or peripheral lesion, the surgeon needs to manually rotate the patient’s head or eye for ablation.
The best results of PTK have been observed in some types of corneal dystrophies, e.g. Reis-Buckler’s, lattice and granular dystrophies, as well as postpterygium scar. Less successful results have been recorded in the degenerative, post-infectious and traumatic conditions. Flattening of the central cornea with hyperopic shift is considered the principal side effect of PTK
Other minor complications include delayed wound healing, postoperative pain, sub-epithelial haze, and reactivation of herpetic lesions. Many patients are currently treated with PTK to reduce the chance of needing penetrating keratoplasty (PK). With further advances in this technique and refinement of PTK, the need for PK will be minimized.
The use of MMC has revitalized the application of surface ablation procedures such as photorefractive keratectomy or phototherapeutic keratectomy for refractive and therapeutic treatments.