PRK Vs Lasik
PRK and Lasik both use an excimer laser begins to reshape the cornea. Although before using the laser to reshape the cornea a part of the outer layer must be removed. Your cornea is made up of epithelium and stroma. Epithelium is on the outer layer of the cornea, and is able to replace itself overtime. The stroma is located beneath the epithelium and is permanent corneal tissue with very limited regenerating properties.
The main difference between the two surgeries is due how much epithelium and stroma is removed before the excimer laser begins to reshape the cornea.
Lasik creates a flap to remove both epithelium and stroma from the cornea, before the excimer laser can begin. While PRK no flap is created, but the epithelial cells are completely removed.
In other words, Lasik requires more of the cornea to be used during surgery, while PRK uses less of the cornea, but the part is does use is completely removed.