Most people who are considering a procedure to reduce or eliminate their dependence on glasses or contact lenses are familiar with the term “LASIK”. This procedure involves reshaping the cornea using an excimer laser. The reshaping is done under a “flap” of cornea tissue which is cut and lifted and then put back in place after the laser treatment is performed.. There is however another procedure that uses the same excimer laser to reshape the cornea however, instead of doing the procedure under a flap it does it right on the surface of the eye. This procedure is called PRK (photorefractive keratectomy) although it has also been referred to as LASEK, epi LASIK, and Advanced Surface Ablation (ASA). In my practice we just refer to it as PRK and it is the procedure we recommend to most patients for its safety and excellent outcomes. We like PRK because we get the same reshaping of the cornea as Lasik does without the risk inherent in having a flap. Many of the risks of Lasik are related to the flap itself and by eliminating the flap portion of the procedure you eliminate most of the risk of the procedure What are some of these risks that can be avoided by doing PRK vs Lasik?

First of all there is risk in making or cutting the flap and lifting it. There have been many cases of damage to the cornea during this portion of the surgery and the flap itself can be torn or improperly made leading to problems. Avoiding a flap avoids these issues.

The flap can develop wrinkles (called striae) which can be extremely difficult to remove once they form and these can definitely degrade the quality of vision. I believe that micro striae or very fine wrinkles in the flap are extremely common and probably seen in the majority of Lasik flaps to some small degree. These may or may not affect vision depending on various factors but in some cases there is no doubt that they definitely do degrade the quality of vision and are extremely difficult or impossible to completely eliminate..

Epithelium can grow under the flap a condition referred to as epithelial ingrowth and this can lead to loss of vision with the need to relift, suture or even remove the flap. Normally epithelium covers the surface of the eye like wallpaper but when the flap is lifted epithelium can get under the flap and grow in the interspace leading to loss of supply of nutrients to the flap and damage or “melting” of the flap. This may be an urgent condition. Avoiding a flap avoids this potential risk.

When a flap is cut it cuts cornea nerves and leads to decreased sensation in the cornea which can lead to development or worsening of dry eye. PRK does not involve cutting the cornea so it spares more nerves and leads to less risk of decreased cornea sensation and resultant dry eye problems.

In some cases cutting a Lasik flap can weaken and destabilize the cornea leading to further shape changes that are progressive and lead to loss of vision. This condition is called “post Lasik Ectasia”. Our understanding of which corneas are at risk to develop this problem is still growing but the fact remains that we don’t always know beforehand which corneas are absolutely safe to cut a flap on. By doing PRK you avoid cutting a flap and by sparing this tissue you greatly reduce or even eliminate the risk of weakening the cornea and destabilizing it which can lead to ectasia. This is why PRK is the procedure of choice for patients with thinner corneas or unusual cornea shapes. Since we can’t predict with complete certainly who will develop ectasia after cutting a flap we can simply avoid this risk by doing PRK and avoiding the flap altogether.

The flap once it’s cut it never completely heals, it only seals at the edges like a manila envelope. An injury to the eye down the road can lead to the flap being lifted, elevated, damaged or lost. I’ve seen patients with damage to their cornea flaps due to airbag deployment years after Lasik and this is why for years the military has preferred PRK to Lasik, to reduce the risk of injury in the field. I always prefer PRK to Lasik in fighters (boxers/Karate etc.) basketball players who might get poked in the eye, and other various professions like dog groomers where an eye might accidently get a finger (or paw) in it. The risk of injury is less because there is no flap to disturb.

Because the flap never heals there is potential space there and this space can become a collection site for fluid or even inflammatory cells. We have seen patients years after Lasik with marked decrease in vision due to fluid in the interface caused by elevated pressure or inflammation. This fluid can degrade vision significantly and take a long time to completely reabsorb.

From reading the above most people would wonder why anyone would choose to have Lasik and the reason is simple. Lasik provides a quicker and more comfortable post operative recovery period than does PRK. In performing PRK we remove the epithelium on the surface of the cornea and then do the laser reshaping. The epithelium takes a few days to heal and usually does so under a clear bandage contact lens which is removed after 3 or 4 days when the epithelium has healed. Usually during this time vision is not very good and the eyes can feel somewhat irritated (although this is usually well controlled by medication). Although PRK ultimately provides a visual outcome which is as good or better than Lasik it takes a few weeks for the vision to “crisp up” so that after a week or two the vision may be good but not great whereas Lasik has much more of an immediate “wow” factor. Another issue with PRK is that the eyes will need to be protected from strong sun exposure with sunglasses for the first few months after the procedure to protect the corneas from developing haze. This risk is significantly reduced with the use of medication applied to the cornea during the procedure (a step I take routinely) but it is still advised to protect the eyes from strong sun exposure during the first few months after PRK .

Some patients don’t have a choice between PRK or Lasik. Many patients can only have PRK because the cornea is too thin or has a “funny shape” making Lasik too risky. In these cases we only offer PRK. The rest of patients may choose between these two and they must decide if they are more interested in a faster recovery or avoiding risk. We usually implore patients to consider and undertake the safest procedure and in my mind this is clearly PRK because by eliminating the flap you eliminate much of the risk inherent in Lasik.

Steven G. Safran, MD, PA