A Comparative Study Between Laser and Manual Removal of Corneal Epithelium for Photorefractive Keratectomy

Photorefractive keratectomy (PRK) is a laser eye surgery used to ablate the corneal stroma to correct visual refractive errors . PRK was developed in 1983 by Dr. Steven Trokel and colleagues and first performed in 1987 by Dr. Theo Seiler in Berlin. After receiving approval by the US Food and Drug Administration (FDA) in 1996, PRK was briefly the preferred surgical treatment of ametropia as it provided more predictable and stable results than incisional keratotomy. However, the number of PRK procedures fell in the late 1990s with the growing popularity of laser in situ keratomileusis (LASIK).

The study aims to compare the visual and refractive outcomes along with the pain score and patient satisfaction after photorefractive keratectomy in patients who underwent transepithelial or mechanical removal technique

Today, LASIK remains the most commonly performed visual refractive surgery; nonetheless, there remain select situations in which PRK may be preferable, such as post penetrating keratoplasty , in thin corneas , irregular topographies , treatment of some LASIK flap complications or residual refractive errors after LASIK, It is also indicated in patients that have a high risk for traumatic postoperative flap dislocation as athletes .Several modifications of the traditional PRK have been introduced in an attempt to overcome drawbacks of postoperative pain and corneal haze and irregular epithelial healing associated with the procedure .PRK employs an excimer laser ablation of the anterior corneal stroma beneath the epithelium .The first step of PRK is the removal of the superficial epithelial cells, which may be through a variety of techniques such as mechanical removal with spatula , application of a diluted alcohol solution , use a rotatory brush or transepithelial laser . Each of these techniques should be performed quickly to avoid desiccation and skillfully to avoid nicking Bowman's layer.

The first technique, Mechanical debridement, involves using a blunt spatula to scrape off epithelium from the periphery toward the center. The next step is wiping a sponge hydrated with balanced salt solution (BSS) or carboxymethylcellulose 0.5% across the cornea. This technique benefits from not depending on laser optics; however, mechanical debridement tends to be a lengthy process in inexperienced surgeons, which subsequently increases patient anxiety and reduces stromal hydration .

In the late 1990s, Transepithelial PRK was introduced as an alternative laser-assisted method for epithelial removal . The advantages of this method have been cited as minimum surgical time, zero contact of laser machine with corneal surface, shorter time for surface healing and visual correction, and decreased post-operative discomfort and dry eyes,this technique is popular among patients but requires a longer time for mastery.

Eligibility Criteria:
Inclusion Criteria:

* • Age : older than 18 years old .

  * Gender: Include both males and females.
  * Stable refraction for at least 12 months .
  * Intraocular pressure less than 21mmHg.
  * A period without wearing contact lenses (more than 4 days for soft , more than 2 weeks for rigid contact lenses )
  * No history of any Autoimmune disease .
  * The refractive error must be one that can be treated by PRK

Exclusion Criteria:

* _ patients with any eye disease (significant cataract or unstable glaucoma )

  * uncontrolled external disease such as blepharitis, dry eye syndrome, and atopy/allergy.
  * patients with Keratoconus and other abnormalities of the cornea such as corneal ectasias , thinning , edema , interstitial or neurotrophic keratitis and extensive vascularisation .
  * Patients with active systemic connective tissue disease such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA)
  * Ineligibility for Surgery: Exclude patients who are not suitable candidates for surgery .
  * Consider excluding pregnant or lactating women .
  * Patients unwilling to participate in the study .