LASIK (Laser-Assisted In Situ Keratomileusis) reshapes the cornea to correct common vision problems. While initial surgery provides excellent results for most patients, a small percentage may experience decreased vision quality over time or retain a minor refractive error. The procedure can often be performed a second time through a process known as a LASIK enhancement or retreatment. This follow-up surgery corrects residual refractive errors and fine-tunes the initial outcome.
Reasons Why Vision May Change After LASIK
Patients may seek retreatment if the initial laser correction resulted in a residual refractive error. This error occurs when the correction was not perfectly calibrated, leading to undercorrection (retaining some original error) or, less commonly, overcorrection. These minor errors often become noticeable only after the eye has fully healed and stabilized in the months following the first surgery.
Vision changes can also result from biological regression, which is the eye’s natural healing response causing a gradual shift back toward the original prescription. This slow return of refractive error is more common in patients who started with a high prescription. The remodeling of the cornea’s epithelial layer, the outermost surface, causes this refractive shift over time. Astigmatism may also be present as a residual error that can be addressed with an enhancement procedure.
Changes unrelated to the initial surgery can also affect vision over many years. Examples include the natural development of cataracts or presbyopia. Presbyopia is an age-related stiffening of the natural lens that makes near focus difficult, which LASIK does not prevent. These conditions are distinct from a true LASIK regression and require different treatments than a simple enhancement.
Essential Criteria for LASIK Retreatment Eligibility
The most important factor for eligibility is the amount of corneal tissue remaining after the initial surgery. The cornea must be thick enough to ensure the procedure can be performed safely without compromising the eye’s structural integrity. Preserving a specific safety margin of tissue prevents corneal ectasia, a serious complication where the cornea bulges outward due to weakness.
The untouched tissue underlying the initial flap, called the residual stromal bed, must maintain a minimum thickness. The FDA recommends this bed be at least 250 micrometers thick, but many surgeons prefer a greater margin (often 270 to 300 micrometers) for additional safety and to allow for potential future enhancements. This measurement is determined through diagnostic tests like corneal pachymetry and topography, which map the corneal surface and measure its thickness.
A patient’s prescription must also be stable for a defined period before an enhancement is considered. The refractive error should not have changed for at least six months to one year after the initial LASIK procedure. This stability ensures the surgeon corrects a final, settled error, not a temporary fluctuation. The patient must also have good overall eye health, free from conditions like uncontrolled dry eye, cataracts, or glaucoma, which could interfere with the enhancement’s outcome.
The Retreatment Procedure Explained
If an enhancement is safe, the surgeon uses one of two primary methods to deliver the laser correction. The preferred technique, especially soon after the original surgery, is to simply lift the existing corneal flap. The original flap never completely seals and can be gently separated from the underlying corneal tissue using a fine instrument.
Once the flap is lifted, the excimer laser precisely reshapes the exposed stromal bed to correct the residual refractive error. The flap is then repositioned, where it adheres without the need for stitches. This flap-lifting method is favored because the visual recovery time is rapid, similar to the original LASIK procedure.
If lifting the flap carries too high a risk, perhaps due to the time passed since the original surgery or concerns about epithelial ingrowth, an alternative procedure is used. This alternative is a surface ablation technique, such as Photorefractive Keratectomy (PRK). In PRK, the laser treatment is applied directly to the surface of the original flap after the outer epithelial layer is removed. While PRK is effective, recovery is generally longer and involves more initial discomfort than the flap-lift method.