Halo vision is the perception of bright circles or rings of light that appear to surround a light source. This visual phenomenon results from the way light bends or diffracts as it enters the eye. For someone experiencing this symptom, streetlights, headlights, or a bare bulb might appear to have a luminous, circular aura.
Describing the Visual Experience
Halos typically manifest as one or more concentric rings of light encircling a bright point source. These luminous rings often display a spectrum of colors, commonly appearing as blue, green, white, or resembling a rainbow effect. The appearance of halos is most pronounced in low-light environments, such as during night driving or when viewing lights in a darkened room.
This light scattering is exacerbated in the dark because the pupils dilate, allowing light to enter the eye through the peripheral parts of the lens and cornea. The underlying mechanism involves light diffraction, which is the scattering or spreading of light rays as they pass through small obstacles or irregularities in the eye.
When these structures develop microscopic imperfections or changes in curvature, light is scattered instead of being perfectly focused onto the retina, creating the visible ring pattern. This effect is an example of a higher-order aberration, meaning the light rays fail to converge at a single, sharp focal point.
Common Causes of Halos
Numerous physiological and medical conditions can lead to the diffraction of light that causes halo vision. One frequent group of causes relates to the cornea. Dry eye syndrome can cause microscopic irregularities on the corneal surface, which scatter incoming light and generate halos.
Temporary corneal edema, or swelling due to fluid retention, can also distort the light path. This swelling can occur in conditions like Fuchs’ dystrophy or may be related to contact lens overwear. A common cause of temporary halos is the healing process following refractive surgeries like LASIK or PRK, where post-surgical corneal swelling is expected.
Another significant cause involves the eye’s lens, particularly the development of cataracts. As the natural lens becomes clouded and opaque with age, the scattered light passing through the dense areas creates the distinct halo effect. Halos can also be a side effect following cataract surgery if a multifocal intraocular lens is used, as these lenses are designed to split light for different focal points.
A more urgent cause is acute angle-closure glaucoma, which involves a sudden spike in intraocular pressure. This pressure increase causes immediate corneal swelling, leading to the rapid onset of often colored halos. Additionally, certain systemic medications or wearing an outdated prescription can temporarily affect tear film stability or light refraction, thereby inducing halos as a transient side effect.
Distinguishing Halos from Glare and Starbursts
Halos, glare, and starbursts are distinct visual phenomena resulting from different types of light disruption. Halo vision is characterized by the appearance of distinct, circular, or rainbow-colored rings surrounding a light source. The boundary of the ring is typically well-defined, separating the light source from the surrounding darkness.
Glare, in contrast, is perceived as an excessive brightness or uncomfortable light that reduces contrast and often makes it difficult to see surrounding objects. Glare is caused by a general scattering of light across the visual field, often making the light source appear overwhelmingly bright without the defined ring structure of a halo. This symptom is often described as a blinding effect that obstructs vision.
Starbursts, also known as radial spokes, present as lines or rays that radiate outward from a central light source. Unlike the circular form of a halo, starbursts resemble an asterisk or star pattern, where the light is stretched into multiple thin, distinct lines. Recognizing the specific visual pattern is helpful for accurately describing the experience to an eye care professional.
When to Seek Professional Help and Treatment Options
While occasional, faint halos in low light may be benign, certain associated symptoms necessitate immediate medical attention. The sudden onset of halos, especially when combined with intense eye pain, headache, nausea, or rapid loss of vision, is a medical emergency that could indicate acute angle-closure glaucoma. Any rapid or significant change in the intensity or frequency of halo vision should prompt a timely consultation.
Treatment for halo vision focuses on resolving the underlying cause of the light diffraction. If the cause is dry eye, lubricating eye drops or prescription anti-inflammatory drops can restore the smoothness of the corneal surface. For halos caused by advanced cataracts, surgical removal of the clouded natural lens and replacement with a clear intraocular lens is the definitive corrective procedure.
Halos related to elevated intraocular pressure from glaucoma are managed with specific medications, such as eye drops or oral agents, that lower the pressure inside the eye. Non-medical management techniques can also provide symptomatic relief, including the use of specialized contact lenses or glasses with anti-reflective coatings to reduce light scatter. Modifying the environment by using dimmer switches or increasing overall ambient light can minimize the pupil dilation that often exacerbates the perception of halos.