Photorefractive Keratectomy (PRK) is a widely performed laser eye surgery correcting refractive errors like nearsightedness, farsightedness, and astigmatism. This procedure reshapes the cornea to improve vision, offering an alternative to glasses or contact lenses. While generally safe and effective, PRK can lead to corneal scars, often called PRK scars. This article explores these corneal changes and their management.
Understanding PRK Scars
PRK scars are corneal haze or subepithelial fibrosis, a corneal tissue response to laser treatment. These scars appear as cloudiness or opacity within the normally clear corneal stroma, just beneath the surface. Their appearance ranges from a faint film to a denser, noticeable milky white or grayish discoloration.
Corneal haze develops weeks to months after PRK surgery, often peaking around three to six months before gradually regressing. Haze varies significantly among individuals; some experience mild, clinically insignificant clouding that does not affect vision. Others develop denser haze that can interfere with optical clarity. Haze classification ranges from grade 0 (clear cornea) to grade 4 (dense opacity).
Why PRK Scars Form
PRK scar formation is a biological healing response triggered by corneal epithelium removal during the procedure. This injury activates specialized keratocytes within the corneal stroma. These quiescent keratocytes transform into active myofibroblasts.
Myofibroblasts produce and deposit disorganized collagen fibers and other extracellular matrix components in the anterior stroma. This irregular deposition, unlike organized collagen in a healthy cornea, scatters light, causing haze. Factors contributing to scarring include individual healing variations, laser ablation depth, and post-operative inflammation. Prolonged UV light exposure after surgery can also increase haze likelihood and density.
Impact on Vision
PRK scars, or corneal haze, affect visual quality based on opacity density and location. Mild haze (grade 0.5 or 1) has no noticeable impact on best-corrected visual acuity or daily vision. These subtle changes may only be detectable upon microscopic examination.
Denser haze (grade 2 or higher) can lead to noticeable visual symptoms. Patients may experience increased glare and halos around lights, especially in low-light conditions, due to light scattering by disorganized collagen. Reduced contrast sensitivity is another common complaint. In severe cases, dense, centrally located haze can significantly decrease best-corrected visual acuity, requiring further intervention.
Managing PRK Scars
When PRK scars or corneal haze compromise vision, several management strategies exist. The initial and most common treatment involves topical corticosteroids. These anti-inflammatory eye drops suppress myofibroblast activity and reduce inflammation, minimizing further collagen deposition and promoting haze regression. The regimen involves a tapering dose over several months.
For significant or persistent haze unresponsive to corticosteroids, other interventions may be considered. Phototherapeutic Keratectomy (PTK) is an excimer laser procedure that precisely removes scarred corneal tissue to restore optical clarity. This procedure is reserved for visually significant and stable haze. In rare, severe instances where extensive scarring causes profound vision loss and is unresponsive to other treatments, a corneal transplant may be considered.
Preventing PRK Scars
Preventing significant PRK scars involves a multi-faceted approach, starting before surgery. Careful pre-operative patient selection is important, as individuals with higher refractive errors or a history of abnormal wound healing may be at increased risk. Surgeons consider these factors when determining suitability for PRK.
During surgery, intra-operative techniques minimize scarring. Applying Mitomycin-C (MMC), an anti-metabolite, to the corneal surface after laser ablation is common. MMC inhibits keratocyte and myofibroblast activity, reducing the fibrotic response.
Post-operative care is also important, emphasizing adherence to prescribed corticosteroid eye drops to modulate healing and reduce inflammation. Protecting eyes from harmful UV light with sunglasses for several months after surgery is recommended, as UV radiation can stimulate scar formation. Regular follow-up appointments allow monitoring and treatment adjustment.