Glare and halos are common complications which can occur after surgery. They are more likely to occur in people who are highly myopic or those who have recently undergone LASIK. Even so, with newer lasers, very few patients complain about severe disabling glare.
Many patients often use the 2 terms – glare and halos interchangeably, which can lead to much confusion. The distinction between these 2 side effects is difficult since it is dependent on the patient’s description of the problem. Glare is caused by light being scattered by any loss of media transparency through things like haze in the cornea. Halos on the other hand are caused by residual refractive power after laser correction, or if the pupil dilates beyond the optical zone of treatment. In this instance, light is allowed to pass around the treated area of the cornea and this leads to a defocused ring of light being seen.
Many times, glare and halos result from poor centration of the laser treatment and small treatment zones. Severe glare is usually temporary and occurs early in the healing phase. In some instances, patients may have problems with dim lighting and night vision. This is due to a combination of slight undercorrection and stray light entering the pupil at night. Fortunately for many patients, the problem eventually solves itself because there is less pupil dilation as one ages.
Some studies have indicated that night-vision disturbance occurs in 25 to 35 per cent of patients treated by LASIK with a 6.00 millimetre optical zone. The incidence of night vision problems has been found to be more frequent in patients who have large pupils, small ablation zones and high attempted corrections.
However studies have also shown that 25 per cent of patients who have undergone LASIK have had night-vision problems prior to their refractive surgery. This has been attributed to uncorrected refractive error, large pupils and irregular astigmatism. A few of the newer lasers like the Allegretto Eye-Q laser have improved optical zone size and improved corneal profiles, reducing the incidence of glare and halos significantly.