LASIK (Laser-Assisted In Situ Keratomileusis) is a widely performed procedure designed to correct common vision issues like nearsightedness, farsightedness, and astigmatism. It works by precisely reshaping the cornea, the clear front surface of the eye, to improve how light focuses on the retina. While the procedure is highly effective for improving daytime visual acuity, a common concern among potential patients is the quality of their vision under low-light conditions. These post-operative visual disturbances at night are a recognized phenomenon, prompting a closer look at the changes the procedure introduces to the eye’s optical system.
Specific Visual Disturbances in Low Light
The visual symptoms patients report after LASIK primarily involve lights appearing distorted when the environment is dim, often referred to collectively as night glare. These distortions manifest in distinct ways, with the three most common being halos, glare, and starbursts. Halos appear as luminous rings encircling a light source, such as a streetlight or headlight. This effect causes a distracting glow around the object and results from light scattering within the eye.
Glare is often described as an overall excessive brightness or glow emanating from a light source, which can feel dazzling or uncomfortable and reduce contrast. Starbursts appear as streaks or spikes radiating outwards from a central point of light, giving the appearance of a star-like pattern spreading across the field of vision. While these phenomena are often temporary, lasting weeks or months as the eye heals, they can occasionally persist and interfere with activities like driving at night.
The Mechanisms Behind Reduced Night Vision Quality
The decrease in night vision quality following LASIK stems from alterations to the corneal surface that affect how light is processed, particularly when the pupil is dilated. One primary cause is the induction of microscopic imperfections in the corneal shape, known as higher-order aberrations (HOAs). These HOAs are optical errors beyond the typical refractive errors that LASIK aims to correct. The laser reshaping process can introduce these subtle distortions, which scatter light and reduce the overall quality of the image perceived by the retina.
Specifically, aberrations like spherical aberration, coma, and secondary astigmatism are strongly correlated with post-LASIK halos and night vision disturbance. Spherical aberration occurs when light rays passing through the periphery of the lens or cornea focus at a different point than those passing through the center. This is exacerbated when the eye’s natural curvature is altered to be flatter, a common outcome of myopia correction.
A second factor is the relationship between the treated corneal area and the eye’s pupil size in darkness. In low-light environments, the pupil naturally dilates to let in maximum light, sometimes reaching a diameter of 6 millimeters or more. If the laser’s treatment zone (ablation zone) is smaller than the widely dilated pupil, the edges of the pupil allow light to pass through the untreated peripheral cornea.
This light then hits the retina without being properly refracted, mixing with the corrected light and causing scattering and distortion. The presence of HOAs combined with a dilated pupil that extends beyond the treatment zone is a powerful mechanism for night vision issues.
Modern Technologies to Minimize Risk
Current LASIK technologies have made significant advancements to minimize the risk of poor night vision quality. The primary tool for this mitigation is Wavefront-Guided LASIK, also known as Custom LASIK. This specialized procedure uses an aberrometer to create a highly detailed, three-dimensional map of the eye’s unique optical imperfections, including higher-order aberrations.
The excimer laser treatment is then customized based on this map, allowing the surgeon to correct the basic refractive error and many of the subtle HOAs that contribute to night vision problems. This personalized approach significantly reduces the chance of post-operative night-vision disturbances, such as glare and halos, compared to conventional LASIK procedures.
Another crucial advancement is the routine use of larger optical treatment zones during the procedure. Surgeons now aim to create an ablation zone large enough to accommodate the patient’s maximum pupil dilation in the dark. By treating a broader area of the cornea, the risk of light passing through the untreated peripheral tissue when the pupil is wide open is substantially reduced.
Pre-operative screening and patient selection also play a role in risk mitigation. Careful measurement of the pupil’s size under scotopic (dark) conditions helps surgeons identify patients who may be at a higher risk of night vision issues. For those with very large scotopic pupils or high prescriptions, a customized treatment plan or a larger optical zone is advised to ensure the best possible visual outcome both day and night.