PRK – Photo-Refractive Keratectomy differs from LASIK in that the Excimer laser is applied directly to the corneal surface to smoothly reshape this surface and correct the refractive error.
PRK involves the manual removal of the most superficial layer of the cornea (the epithelium) or using the laser to directly remove the epithelium (TEMLA), before the laser correction begins. The underlying corneal tissue surface is then re-shaped with the Excimer laser. After the surgery, a contact lens is placed over the eye to assist with healing and comfort.
The surface epithelial layer heals over several days to cover the treated area and grows to the new shape. Some discomfort can occur during this healing process. Vision may be blurred until the epithelium has regrown, usually within 4 to 7 days. Further improvement typically continues over several weeks.
Corneal haze (scarring) is a significant side effect with PRK as the eye heals; haze can cause or exacerbate symptoms such as regression, glare and haloes. However, PRK continues to be an effective, safe treatment for low refractive errors. The higher the refractive error, the greater the potential for scarring with PRK.
LASEK – Laser Assisted Epithelial Keratomileusis LASEK is a slight modification to the PRK procedure. After the Excimer laser treatment, the thin layer of epithelium is placed back into position and a contact lens applied to assist with healing and comfort levels. This treatment has slightly longer healing times than PRK and is now rarely performed. Results were identical to PRK.
TEMLA – Trans-Epithelial Minimal Laser Ablation is a further modification to PRK. The Excimer laser is applied directly to “vaporise” the surface epithelium before the laser reaches the permanent layer of the cornea (the stroma). Unfortunately, the epithelium is not of uniform thickness and visual results are more variable due to the less precise stromal ablation. Although still occasionally used, this technique has largely been abandoned except for damaged, scarred corneas.
ASLA – Advanced Surface Laser Ablation is another word for standard PRK. In the 1990’s, the original broad beam lasers were replaced by “new technology” flying spot lasers. All modern excimer lasers now use flying spot techniques.