During the past 20 years, the use of the excimer laser has proven to be an effective and safe method to correct nearsightedness, farsightedness and astigmatism. The most commonly used vision correction techniques are PRK and LASIK. PRK was performed before LASIK was developed as a technique, but PRK remains a popular, proven, safe and very reliable method to correct the vision. When LASIK was first developed, it was thought that it may replace PRK for most patients due to the lower risk of corneal haze with LASIK when using the first generation lasers in the 1990s. However, the risk of corneal haze has dramatically decreased with PRK due to improved laser ablation patterns and the use of intraoperative medication that reduces the risk of haze. For this reason, PRK has experienced a resurgence in popularity in recent years and in many cases, it is viewed as the superior method of vision correction.
LASIK has limitations, primarily due to the need for additional corneal tissue to create a corneal LASIK flap. Even when the flap is created with a laser, the thin flap is comprised of tissue that would otherwise remain intact in the cornea. PRK is usually advised when corneas are too thin for LASIK to be performed safely. However, some surgeons believe that for any given level of correction, after excimer laser treatment, PRK may be a safer proc
edure than LASIK because leaving more corneal tissue intact may result in a stronger post operative cornea and this may translate to less risk of postoperative complications such as corneal ectasia (thinning of the cornea). In addition, there is zero risk of any flap complication such as a wrinkled or displaced corneal flap.
The characteristics of corneal healing after excimer laser surgery vary with the procedure.
During PRK, the corneal epithelium, or skin is removed from the corneal surface, using any of a number of techniques: laser ablation, mechanical debridement, or alcohol assisted debridement. Within 24 hours after PRK, the corneal epithelium has begun to heal. A layer of fibrinogen, a protein involved in clotting may appear on the corneal surface as the first step in healing. During the next 2-3 days the corneal skin cells multiply and cover the treated area. Healing times may vary and in some patients, it may take 3-4 days, or longer for the epithelium to cover the treated surface. However, it may take several weeks for the new corneal epithelial cells to adhere normally to the underlying surface and for this reason, frequent artificial tears can be helpful in the immediate days and weeks following PRK.
Corneal haze was formerly a common complication or side effect of PRK, however the incidence of haze is now very low, especially when new lasers are used. Differences in techniques during PRK may affect the development of haze which is due to the deposition of collagen in the cornea. At King LASIK, we rarely see significant corneal haze any longer, due in part to newer lasers, surgical techniques and the use of mitomycin, a medication that is applied during PRK to reduce the risk of corneal haze. Now, the risk of corneal haze with PRK and LASIK are similarly very low with either technique.
When LASIK was first developed as a surgical technique, it became more popular than PRK due to the relatively rapid recovery of vision, minimal risk of corneal haze, and early refractive predictability. Because corneal epithelial cells and corneal keratocytes are minimally activated with LASIK, even very mild haze is only very rarely seen after LASIK. The wound healing with LASIK tends to occur at the flap margin, where the corneal epithelium covers the incision and there may be some collagen deposition at the flap edge. However, the flap bed (otherwise known as the intrastromal lamella) heals only very weakly. Animal studies have shown that even months after LASIK, the healing is not complete. In our experience, it is possible to easily lift a LASIK flap many years after a LASIK procedure, suggesting that LASIK wounds never fully heal, and this may increase the susceptibility of the cornea to trauma from sports or accidents. The flap is believed to adhere to the underlying cornea due to a variety of factors, such as the pumping action of corneal endothelial cells, creating a suction effect on the flap, the overlying layer of corneal epithelial cells and perhaps some collagen deposition in the flap interface.
It is believed that dry eye may be more common after LASIK due to the effect of severing the corneal nerves. Corneal sensitivity has been shown to be decreased to a greater extent following LASIK compared to following PRK.
A technique called LASEK was popularized in the early 2000′s as an ‘alternative’ to LASIK and PRK. The idea is that a corneal epithelial flap is created and this covers the area of ablation after the excimer laser treatment. However, this technique did not prove to be any more effective or safer than PRK, which was already highly effective and safe. Most surgeons consider LASEK to be a variant of PRK with similar wound healing characteristics.
Typically, after PRK, most patients will be able to drive and resume normal activities within 3-5 days. After LASIK, most patients see well enough to drive within 1 day. After PRK, the vision can be very good on the first postoperative day (similar to LASIK in many cases), but due to the corneal healing and possible use of Tylenol #3, we do not advise that patients drive until the contact lens is removed and the vision is tested.
Both LASIK and PRK have been performed on millions of eyes around the world over the past 20 years. Dr. King has performed tens of thousands of each of these procedures. Dr. King and his experienced team of professionals look forward to answering any questions that you might have about the options to correct your vision.