Halos in vision are bright, colored, or white rings that appear to encircle light sources like streetlights, car headlights, or indoor lamps. This visual phenomenon is frequently more noticeable in low-light conditions when the pupil is naturally dilated. While seeing a faint halo can be a normal optical occurrence, a sudden change or persistent presence of halos can indicate an underlying eye health issue requiring medical attention.
The Optical Mechanism of Halos
The appearance of a halo is a result of light scattering or diffraction as it enters the eye, preventing it from focusing precisely on the retina. Normally, the cornea and the lens work together to refract light into a sharp, single focal point. When imperfections exist in the optical pathway, incoming light rays are split and bent abnormally before reaching the light-sensitive tissues at the back of the eye. This scattering is caused by microscopic irregularities or particles within the transparent structures of the eye, primarily the cornea and the crystalline lens, which redirect light and create the luminous, ring-like pattern.
Common and Temporary Causes
Not every instance of a visual halo suggests a disease; many common factors can temporarily disrupt the eye’s refractive surfaces. One of the most frequent causes is dry eye syndrome, where an unstable or insufficient tear film coats the cornea. This uneven film creates a rough surface that scatters light, often leading to halos that worsen late in the day or after prolonged screen use.
Another cause relates to the recovery period following refractive surgeries, such as LASIK or PRK. Temporary corneal swelling or reshaping during the healing process can cause light scattering, resulting in noticeable halos, especially at night. This post-surgical symptom typically diminishes within weeks or months as the cornea fully heals.
Issues related to contact lenses, including improper fit, surface debris, or overwearing, can also induce halo perception. In dim light, the pupil dilates, allowing more peripheral light rays to enter the eye. For individuals with uncorrected refractive errors, this larger pupil size permits more scattered light to reach the retina, making night-time halos a common, non-pathological experience.
Halos Linked to Serious Eye Conditions
When halos are persistent, intense, or accompanied by other symptoms, they may signal a more serious ocular condition affecting the clarity of the cornea or the lens. Acute angle-closure glaucoma is a medical emergency where a sudden, severe rise in intraocular pressure causes the cornea to swell (corneal edema). This fluid buildup dramatically alters the cornea’s transparency, leading to the rapid onset of colored or rainbow-like halos, often accompanied by severe eye pain, headache, nausea, and blurred vision.
Cataracts involve the progressive clouding of the eye’s natural lens. As the proteins in the lens break down and clump together, the lens loses clarity, causing light disruption, glare, and halos, particularly at night.
Fuchs’ dystrophy is a genetic condition where the endothelial cells lining the back of the cornea gradually die off, impairing the cornea’s ability to pump out excess fluid. This persistent corneal edema causes the cornea to become thick and hazy, scattering light and leading to persistent halos and blurred vision that are often most pronounced in the morning. The design of certain multifocal intraocular lenses used in cataract surgery can also intentionally split light to achieve multiple focal points, which may result in a permanent perception of halos.
When to Consult an Eye Care Professional
Any sudden change in vision, including the abrupt onset of halos, warrants prompt consultation with an optometrist or ophthalmologist. It is especially urgent if the halos are associated with pain, redness, or nausea, as these are classic signs of acute angle-closure glaucoma, which requires immediate treatment to prevent irreversible vision loss.
An eye care professional will perform a comprehensive eye examination to determine the underlying cause of the halos. This process includes a visual acuity test and a slit lamp examination, allowing the doctor to view the cornea and lens under high magnification to check for signs of edema, clouding, or surface irregularities. Measurement of the intraocular pressure (tonometry) is also necessary to rule out pressure-related conditions like glaucoma.
Management of halos depends entirely on the specific diagnosis revealed by these tests. Treatment may involve simple measures like prescribing lubricating eye drops for dry eyes or updating an eyeglass prescription. For conditions like advanced cataracts or glaucoma, treatment may necessitate surgical intervention or medication to manage intraocular pressure.