PRK versus LASIK

There have been a number of studies comparing LASIK to PRK. LASIK is associated with decreased inflammation and quicker recovery, but at the cost of decreased expression of Nerve Growth Factor (NGF) at the surgical bed. PRK, on the other hand, has longer recovery time with more postoperative discomfort and irritation, but rates of ocular dryness are less, as only the epithelium is denuded in this approach. LASIK, on the other hand, involves creation of a corneal flap. The medical literature is not uniform, however, regarding comparative effects on ocular dryness, although the majority of research supports PRK as causing less reduction in tear film. Surgical technique has improved with time, and a more recent study has shown no difference in ocular dryness in LASIK or PRK at 12 months, as compared to pre-operative baseline, although interval assessments at months 1, 3 and 6 did show dryness in both groups. Quantitative changes occurring at the eye surface are more pronounced with LASIK, but more irritation, pain and eyelid sticking are felt with PRK, which could be related to increased denervation with LASIK. A Cochrane Systematic review compared PRK and Lasik; it concludes that LASIK may be better in terms of recovery time and pain.

PRK does not create a permanent flap in the deeper corneal layers, while LASIK involves a mechanical microtome using a metal blade or a femtosecond laser microtome to create a 'flap' out of the outer cornea. As such, the cornea's structural integrity is less altered by PRK. The LASIK process covers the laser treated area with the flap of tissue which is from 100 to 180 micrometres thick. This flap can mute the nuances of the laser ablation, whereas PRK performs the laser ablation at the outer surface of the cornea. The use of the anti-metabolite mitomycin, which is referred as M-LASEK, can minimize the risk of post-operative haze in persons requiring larger PRK corrections, although the medication can worsen the dry eye that occurs after surgery in some patients.Unlike LASIK, PRK does not involve a knife, microtome, or cutting laser, but there may be more pain and slower visual recovery. Unlike LASIK, PRK does not have an increased risk of dislocated corneal flap, which may occur with trauma after LASIK.