Photorefractive Keratectomy (PRK) and Laser-Assisted In Situ Keratomileusis (LASIK) are the two most common laser vision correction procedures, both using an excimer laser to reshape the cornea. LASIK involves creating a thin flap to access the underlying tissue, allowing for rapid visual recovery. PRK corrects vision by removing the outer layer (epithelium) before applying the laser directly to the surface. It is possible to have PRK as a secondary procedure, known as an enhancement, after initial LASIK surgery. This approach is often considered the safer and preferred method for fine-tuning vision years after the original procedure.
Why Enhancements Are Necessary After LASIK
Even after successful LASIK, patients may experience a slight reduction in visual clarity over time, making an enhancement necessary. The most common reason is a residual refractive error, which is a small amount of nearsightedness, farsightedness, or astigmatism that remains or develops. This can be due to the eye’s natural healing response, sometimes resulting in a slight under- or over-correction.
Another factor is refractive regression, where the eye gradually shifts back toward the original prescription over many years. Subtle remodeling of the corneal tissue or changes in the natural lens due to aging can contribute to this shift. Enhancements are sought when the quality of vision no longer meets the patient’s daily needs.
Technical Rationale for Choosing PRK
When an enhancement is needed after LASIK, the surgeon decides between re-lifting the original flap or performing surface ablation like PRK. PRK is frequently chosen because it offers greater structural safety for the cornea. Re-lifting a long-established flap increases the risk of flap-related complications, such as epithelial ingrowth, where surface cells grow underneath the flap.
Every laser correction removes corneal tissue from the residual stromal bed (RSB) beneath the flap. Maintaining sufficient RSB thickness is necessary to ensure the structural integrity of the cornea. PRK is considered a tissue-sparing procedure because it avoids re-lifting the thicker LASIK flap. Performing the ablation on the surface minimizes disruption to the underlying structure, which helps mitigate the long-term risk of ectasia. Ectasia is a serious condition involving the progressive thinning and bulging of the cornea.
The PRK Enhancement Procedure and Recovery Experience
The PRK enhancement procedure is fundamentally the same as a primary PRK, but it is performed on an altered cornea. The surgeon begins by gently removing the epithelial layer, typically using a soft brush or diluted alcohol solution. The excimer laser is then applied directly to the surface to perform the precise refractive correction.
Unlike a LASIK enhancement, PRK requires the eye to regrow the epithelial layer. A soft bandage contact lens is placed on the eye immediately after the procedure to minimize discomfort and protect the area. This lens remains in place for three to seven days until the new epithelial cells have fully covered the treatment area.
The recovery period for a PRK enhancement is notably longer than with LASIK. Patients should expect moderate discomfort or a gritty sensation for the first few days while the epithelium regenerates. Initial vision is often blurry, and it can take four to six weeks for functional vision to return and several months for final clarity to stabilize. To prevent corneal haze, surgeons often use topical medication like Mitomycin-C during the procedure and prescribe a regimen of steroid eye drops post-operatively.
Other Options for Residual Refractive Error
While PRK is a common choice for a LASIK enhancement, it is not the only option for addressing residual refractive error. For patients needing minimal correction, wearing glasses or specialized contact lenses is the safest, non-invasive solution. This approach avoids additional surgical risk and is preferred if the error is small.
In rare cases, if the residual error is too large for safe laser ablation, or if the cornea is too thin, an intraocular solution may be considered. This involves the implantation of a phakic intraocular lens (ICL), a small, permanent lens placed inside the eye, or a refractive lens exchange, which replaces the eye’s natural lens entirely. These internal lens procedures are reserved for patients with higher degrees of refractive error or when age-related changes, such as early cataract formation, are present.