LASIK, or Laser-Assisted In Situ Keratomileusis, is a well-established refractive procedure designed to correct common vision impairments. Astigmatism occurs when the eye’s front surface, the cornea, or the lens has an irregular, football-like curvature instead of a smooth, spherical shape. This uneven surface causes light to focus incorrectly on the retina, resulting in blurred or distorted vision. LASIK is generally considered a secure and successful option for individuals who meet the necessary health criteria.
How LASIK Corrects the Astigmatic Cornea
Correcting astigmatism with LASIK requires a significantly more complex approach than treating simple nearsightedness or farsightedness. For those conditions, the laser removes tissue in a uniform, spherical pattern. Astigmatism, however, demands a targeted, non-uniform removal of tissue, a process often referred to as toric ablation. The laser must selectively reshape the steeper meridian of the cornea without significantly altering the flatter axis.
Modern LASIK technology achieves this precision through highly sophisticated preoperative mapping and intraoperative guidance systems. Diagnostic tools, such as wavefront aberrometry and topography, create a detailed, three-dimensional map of the cornea’s surface, identifying all irregularities beyond the basic prescription. This map acts as a blueprint, guiding the excimer laser to apply a customized ablation profile. The laser tracks the eye’s movements in real-time, ensuring the focused energy pulse is delivered precisely to the designated area on the cornea to smooth the irregular curvature.
This customized approach is necessary because astigmatism involves two different curvatures, requiring the laser to balance the power across the two principal meridians. By utilizing this detailed data, the surgeon can ensure the laser sculpts the cornea into a more symmetrical shape, allowing light to focus correctly on a single point on the retina.
Safety Profile and Success Rates for Astigmatism Correction
Clinical data repeatedly confirm the high safety profile and effectiveness of LASIK for correcting astigmatism, often achieving visual outcomes comparable to those seen in eyes without cylinder correction. The general safety profile remains high, with serious complications like infection or flap issues occurring very rarely.
Success rates are measured by the patient’s uncorrected visual acuity after the procedure. Studies evaluating outcomes for myopic astigmatism correction show that a large percentage of eyes achieve excellent vision. Specifically, one study found that approximately 89.0% of eyes achieved uncorrected visual acuity of 20/20 or better one year after the procedure. Furthermore, over 98.7% of eyes were able to see 20/40 or better without corrective lenses.
These results indicate that modern laser systems are highly predictable when correcting the irregular curvature of an astigmatic eye. The high rate of achieving 20/40 vision or better is the standard used for meeting the requirement to drive without glasses in most jurisdictions.
Specific Risks and Potential Complications
While the procedure is generally successful, correcting an irregular cornea introduces certain specific risks. One of the primary concerns is residual astigmatism, which occurs when the correction is incomplete, leaving a small amount of cylinder power still present. This can sometimes necessitate an enhancement procedure, or touch-up, to fully correct the remaining error.
A more complex complication relates to induced higher-order aberrations (HOAs), which are subtle irregularities in the eye’s optical system that glasses cannot correct. These HOAs can manifest as visual disturbances like glare, halos, or starbursts, particularly noticeable at night. Treating a high degree of astigmatism may increase the likelihood of inducing these aberrations if the ablation zone is too small or slightly decentralized.
The careful planning provided by modern wavefront and topography-guided systems aims to minimize the induction of these visual artifacts. However, any procedure that reshapes the cornea carries a risk of altering the optical quality in ways that affect contrast sensitivity. Patients with larger pupils may also be more susceptible to experiencing HOAs, as the uncorrected peripheral cornea is exposed when the pupil dilates in the dark.
Determining Patient Suitability
The safety of LASIK for astigmatism relies heavily on a thorough preoperative screening to ensure the patient is a suitable candidate. A fundamental requirement is demonstrating a stable astigmatism prescription for at least one year before the procedure, as instability suggests an underlying issue that could compromise the long-term outcome. The surgeon must confirm the eye’s refractive error is no longer progressing.
Corneal thickness is another important factor, especially when dealing with the non-uniform tissue removal required for astigmatism. A general guideline suggests a minimum corneal thickness of at least 500 micrometers (µm) to safely create the flap and perform the ablation. The final residual stromal bed, the tissue remaining under the flap, must meet a minimum thickness of 250 to 270 µm to maintain the structural integrity of the cornea.
The severity of the astigmatism also plays a role in candidacy. Patients with very high levels of astigmatism may require a greater amount of tissue removal, potentially making them unsuitable for LASIK due to the risk of leaving an inadequate residual stromal bed. In such cases, alternative procedures like Photorefractive Keratectomy (PRK) or implantable lenses may be recommended as safer options.