Glare and Halos
See also: LASIK Risks & Complications
Most of us have some dissatisfaction with our vision when driving at night. This is due in part to our pupils dilating (getting larger) in the dark. As the pupil dilates, the optical quality of the eye worsens. A large pupil makes any uncorrected refractive error more apparent and introduces a vision-degrading effect called spherical aberration. This leads to the perception of glare and halos around headlights and streetlights — even if you haven't had refractive surgery.
Many LASIK patients experience at least some temporary glare and halos in the weeks after surgery. This is usually due to corneal swelling and/or dry eye. This temporary problem is common and different from the persistent variety of night vision problems.
Persistent glare and halos after LASIK have several possible causes. The most common is residual refractive error: Remaining myopia, hyperopia, or astigmatism from an over-response or under-response of your cornea to the treatment (causing an unwanted under-correction or over-correction of your refractive error). In these cases, a pair of prescription eyeglasses or a LASIK enhancement procedure can solve the problem.
Nighttime glare and halos may also occur if your pupils dilate beyond the area of laser treatment in low light conditions, or if the laser ablation (treatment) is not centered properly on your eye. When either of these exists, light can bend irregularly at the junction between the treated and untreated cornea. In many cases, a surgical enhancement or medicated eye drops to reduce pupil diameter when driving at night can solve these problems.
Reducing Glare and Halo Risk
To reduce your risk of glare and halos at night, measurements of the size of your pupils will be taken during your preoperative exam. In general, patients with large pupils and high corrections are at greater risk. Based on these measurements, your eye doctor will be able to advise you of your risk for glare or halos after refractive surgery.
Other causes of glare and halos include postoperative corneal haze and irregular astigmatism caused by corneal surface irregularities.