Seeing starbursts or halos around bright lights, especially at night, is a common visual phenomenon. A starburst is characterized by fine rays or spikes of light radiating outwards from a central light source, while a halo appears as a glowing ring. This effect is a form of optical distortion caused by how light interacts with the eye’s structures before reaching the retina. Examining the mechanics of light within the eye helps determine if the cause is a simple, temporary issue or a symptom of an underlying medical condition.
The Optical Science Behind Light Scatter
The clarity of vision depends on light traveling directly through the eye’s transparent structures to focus sharply on the retina. Starbursts occur when light is scattered, or diverted, as it passes through the eye’s media, including the tear film, cornea, and lens. Instead of converging to a single, focused point, the light rays spread out, resulting in the characteristic spiked pattern. This process is often classified as a form of higher-order aberration, which cannot always be corrected by standard eyeglasses alone.
Scattering happens when light encounters microscopic irregularities on the surface or within the eye’s tissue. A perfectly smooth optical surface transmits light cleanly, but any unevenness causes light to bend or diffract. The degree of this light scatter determines the intensity of the perceived starburst or glare. This effect is most noticeable when looking at concentrated light sources, such as car headlights or streetlamps, against a dark background.
Common and Temporary Causes
The appearance of starbursts is frequently linked to factors that temporarily alter the eye’s optical pathway and are not indicators of serious disease. One common cause is the natural dilation of the pupil in low-light conditions. When the pupil widens, light passes through the periphery of the lens, where minor imperfections or the edge of a contact lens can cause light scatter. Individuals with uncorrected or highly irregular astigmatism, a common refractive error, often see prominent starbursts due to uneven light bending.
Temporary changes to the eye’s surface, such as a thin or irregular tear film caused by dry eyes, can also be responsible for light scatter. Blinking often restores the tear film, momentarily clearing the starburst effect until the tear film destabilizes again. The early period following refractive surgeries, like LASIK or photorefractive keratectomy (PRK), can involve temporary swelling or changes to the corneal shape that lead to starbursts and halos. Even simple issues like condensation, smudges, or scratches on eyeglasses or contact lenses can scatter light and mimic the starburst effect.
Underlying Eye Conditions That Cause Starbursts
When starbursts become persistent, worsen over time, or significantly impair vision, they may indicate a structural change within the eye. Cataracts are a frequent cause, where the normally clear crystalline lens behind the iris becomes cloudy. This clouding is caused by the clumping of lens proteins, which prevents light from passing through cleanly and causes it to scatter widely, resulting in glare and starbursts, particularly at night. The location of the clouding within the lens influences the specific visual distortion; opacities near the center often cause the most intense symptoms.
Another set of conditions involves the cornea, the transparent front dome of the eye. Corneal edema, or swelling, occurs when excess fluid accumulates in the corneal layers, disrupting the precise organization of its collagen fibers. This disruption is a powerful source of light scatter; in conditions like Fuchs’ endothelial dystrophy, the starbursts and hazy vision are often noticeably worse upon waking. Severe chronic dry eye disease can lead to persistent irregularities on the corneal surface, creating a fixed source of light distortion.
High or irregular astigmatism remains a significant mechanical cause of starbursts. The uneven curvature of the cornea or lens causes light to focus in multiple planes instead of one, stretching a point source of light into a line or spike. Certain intraocular lenses implanted during cataract surgery, especially multifocal designs, use concentric rings to achieve multiple focal points. These rings can sometimes cause a low level of light diffraction perceived as starbursts or halos.
When to Seek Professional Consultation
While many instances of starbursts are benign, it is prudent to consult an eye care professional if symptoms are new, rapidly worsening, or interfere with daily activities like driving. Immediate consultation is advised if starbursts are accompanied by other sudden symptoms, such as eye pain, noticeable loss of central vision, or the sudden appearance of flashes of light and new floaters. These signs can signal an acute condition, such as a sharp rise in intraocular pressure, which requires urgent evaluation.
An eye care professional will perform a comprehensive examination to determine the source of the light scatter. This typically includes a slit-lamp examination, which uses a microscope to inspect the anterior structures of the eye, including the tear film, cornea, and lens. Specialized tests like corneal topography can map the precise curvature of the cornea, and a device to measure straylight can quantify the amount of light scatter. Management options range from new eyeglass or contact lens prescriptions to address refractive errors, to medicated eye drops for corneal swelling or dry eye, or a referral for cataract surgery.