Halos and Glare

Recently, the media has placed significant attention on night vision disturbances like halo and glare (halos and glares) following refractive surgery.  In some cases, this problem has been blown out of proportion.  Most patients, including those that have not undergone refractive surgery, experience greater vision difficulty at night than during daylight hours.  This has to do with the pupil getting larger in the dark.  As the pupil gets larger, the optical quality of every eye worsens.  A large pupil makes any uncorrected refractive error more apparent while also introducing the vision-degrading effects called spherical aberration and coma.  This leads to the perception of “glare and halos” even in patients that have not had refractive surgery.  Patients wearing contact lenses and glasses may also note additional “glare and halos” from the extra reflecting surfaces introduced by these corrective lenses.

The vast majority of LASIK patients experience at least some temporary glare and halos during the immediate recovery.  This can last for weeks and is due to corneal swelling and reorganization of the corneal architecture.  Patients in the healing phase need to understand this is normal and different from the persistent variety of night vision problems.

Persisting glare and haloes after LASIK have several possible causes.  The most common is “residual refractive error”, which refers to remaining myopia, hyperopia, or astigmatism from under- or over-response to the treatment.  In these cases, a pair of prescription glasses or a surgical enhancement can solve the problem.  Glare and halos may also occur if the pupil enlarges beyond the area of laser treatment or when there is a decentered ablation.  When either of these exist, light can bend irregularly at the junction between the treated and untreated cornea.  If the pupil is large enough, the irregularly bent light passes into the eye, causing glare and haloes.  Since the pupil gets larger in the dark, glare and haloes are usually most noticeable at nighttime.

There are several treatments for pupil-related night vision problems although none are perfect.  Driving at night with the dome light on can help constrict the pupils although this practice is not legal in certain states.  Alternatively, your doctor can prescribe an eye drop called pilocarpine to shrink the pupil.  In certain patients, this drop may cause focusing spasm and increase the risk of retinal detachment.  Another eye drop for shrinking the pupil is called dapiprazole.  This drop makes the eyes appear red and stings on instillation.  Other drops are under investigation.  Eye color-changing soft contact lenses (with an annular ring of color) may reduce glare and halos by making the functional pupil smaller.  "Over-minused" or over-powered corrective lenses may also cause the pupil to reduce in size.  Some surgeons have suggested performing an enhancement procedure using a laser to enlarge the original treatment zone.  Rigid gas permeable lenses can also help in establishing a larger functional optical zone.

If you have not yet had refractive surgery, the best way to minimize the likelihood of persistent glare and halos related to pupil size is to make sure your doctor carefully measures your pupil size.  In general, patients with large pupils and high corrections are at greater risk.  High degrees of myopia and/or astigmatism can create a sharper junction zone between treated and untreated cornea to potentially scatter light.  Hence, when the pupil size and prescription are considered together – not separately – your doctor should be able to tell you whether your are at low, medium, or high risk for developing this type of glare and halos.  High risk patients may benefit from lasers using a larger treatment size and from upcoming technology.

One suggested treatment for night glare and halos from large pupils has been using anti-reflective coated lenses.  While this type of coating reduces the magnitude of reflections introduced by the spectacle lens itself, it is theoretically useless in removing light scatter derived from the pupil / corneal-treatment size issue.  Nevertheless, some refractive surgeons advocate it as a treatment.

Other causes of glare and halos include haze or scarring of the normally transparent eye tissues, including the cornea and crystalline lens, and also irregular astigmatism caused by corneal surface irregularities.

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