The word halo comes from Greek (άλως) and it is defined as a “circle of light shown around a luminous body”, such as streetlamps or car headlights at night. Halos normally appear in shadowy places or in darkness. They are usually a response to bright lights, but they may come about with certain eye conditions or pathologies.
The most common causes are:
- Cataracts. At a young age, the crystalline lens (the eye's natural lens) is completely transparent and the light can pass through it easily without any issues. With age, the crystalline lens loses its transparency (a cataract forms), causing blurred or reduced vision. In these cases, halos can be a common symptom.
- Ametropia. When the image does not focus properly on the retina and glasses are needed for correction. Ametropias include myopia (large eyes) and difficulty seeing at distance, hypermetropia (small eyes) or difficulty seeing up close, astigmatism (irregular corneas) or blurred or double vision. In all the cases above, halos usually occur in dimly lit conditions, like while driving at night.
- Cornea issues. The cornea is the transparent anterior part of the eye. It is a tissue that acts like a lens, playing a role in the focus of images on the retina. Pathologies that change its shape (like keratoconus, dystrophies, etc) or its transparency (like Fuchs’ corneal dystrophy, cicatricial leukoma, trauma, etc) can cause halos.
- After eye surgery. Some surgical procedures can cause you to see halos, especially at night. Generally, these are temporary phenomenon that will be more intense in the immediate postoperative period and decrease or go away with time (for example, with LASIK surgery, ICL pre crystalline lenses, multifocal intraocular lenses, etc.). In certain cases, this phenomenon is permanent, like in radial keratotomy, due to the change in the cornea.
- Environmental surroundings. In some cases, halos come about in normal conditions without there being any eye pathology involved (for example, when driving in the evening, surfaces that reflect the sunlight, camera flashes, etc.). In these cases, the effect lasts a few seconds or minutes depending on the intensity.
"Some surgical procedures can cause you to see halos, especially at night. Generally, these are temporary phenomenon."
Treatment will mainly depend on the primary cause. If the halos are minimum and only occur in certain light conditions, the use of sunglasses or polarised lenses really helps to reduce this phenomenon. Using the sun visor in the car can also be useful to limit the direct impact of the sun when driving. If the problem is ametropia, especially in cases of myopia or astigmatism, the use of corrective glasses or contact lenses usually fixes the problem. In the case of cataracts, the solution would include cataract surgery and an intraocular lens. It is important to remember that you will see halos with some intraocular lenses, especially multifocal lenses (allowing you to see up close and at distance), in the first few months after surgery. This situation generally improves over time. It is important to take this into account when it comes to choosing the type of intraocular lens to have implanted.