Night Glare and Halos
All people, whether or not they have had LASIK, experience some glare or halos at night. These night-vision disturbances occur when you are in a dark environment and look at a small bright light, such as a headlight or streetlight. Halo is the glow that surrounds the light source, and glare is little spikes of light that appear to emanate from the light source like the rays around a light. Glare and halos occur because the pupil dilates in low-light conditions. The dilated pupil allows more peripheral light rays (rays coming in from the sides) to enter the eye. These rays are more likely to scatter, instead of coming to a precise focus. You perceive the scattered light as glare or halos. Incidentally, this scattering of light from proper focus is why everyone notices that his or her night vision is not as good as their daytime vision.
Some patient experience an increase in these symptoms after LASIK. Although these symptoms do not necessarily interfere with visual sharpness as measured on the Snellen eye chart, they can be bothersome in dim-light conditions, such as driving at night. Some patients may see glare or halos at night during the first month after treatment; however, it is quite uncommon for these side effects to interfere with patients’ activities. The effects usually improve in the first 3 months, and the overwhelming majority of significant glare problems disappear on their own by 6 months. There are treatment options for patients who experience persistent glare or halos. Weak prescription night glasses can help. Wavefront-guided retreatment is also a promising approach.
It’s difficult to predict one patient’s chances of having these symptoms after LASIK. Patients with more severe refractive errors and astigmatism may be more prone to glare and halo effects. Many eye doctors used to believe that patients with larger pupils had a greater chance of developing glare or halos at night, although a number of major studies have now shown that this is not true. Special programs for the laser that allow for larger treatment zones can help reduce the chance of these problems.
The newer wavefront-guided laser treatments has been shown to significantly reduce the night-vision disturbances compared with conventional laser treatment, which is another reason many surgeons recommend it to all eligible patients.