Seeing lines, streaks, starbursts, or halos around light sources is a common visual phenomenon, especially when driving at night. This visual distortion occurs when light entering the eye is scattered or refracted incorrectly, preventing it from focusing cleanly onto the retina. Causes range from simple, non-medical issues outside the eye to complex structural changes within the eye’s components. Understanding the source of the distortion is the first step toward finding a resolution.
Non-Medical Reasons for Streaking
Light diffraction, the slight bending of light waves as they pass the edge of an object, naturally creates minor streaks or rays radiating from a light source. This phenomenon is exaggerated in low-light conditions when the pupil dilates, allowing more scattered light to enter the eye’s periphery.
Interference from external factors can also introduce streaks and glare. The presence of dust, smudges, or scratches on eyeglasses, contact lenses, or a car windshield can scatter the light before it even reaches the eye. Cleaning these surfaces often removes the source of the visual distortion entirely.
Temporary environmental conditions, such as high atmospheric humidity, fog, or moisture on the eye’s surface, can also cause light to scatter. These non-medical causes are usually benign and easily remedied by cleaning or waiting for the environmental factor to dissipate.
Common Surface and Refractive Causes
Persistent visual streaks are often caused by irregularities in the eye’s primary light-focusing structures: the cornea and the lens. These conditions interfere with light rays converging on a single point on the retina. The resulting misalignment is interpreted by the brain as a streak or starburst pattern.
Astigmatism
Astigmatism is a frequent reason for seeing lights with radiating lines or streaks. This refractive error occurs because the cornea or the lens is curved more like a football than a spherical basketball. This irregular shape causes light entering the eye to focus on multiple points, rather than a single sharp point on the retina.
The uneven focusing causes the light from a point source, like a headlight, to be stretched into a line or smear, especially noticeable against a dark background when the pupil is wide. Corrective lenses, known as toric lenses in contacts, are specifically designed to compensate for this uneven curvature, allowing light to focus properly and eliminating the streaking.
Dry Eye and Tear Film Instability
A healthy eye requires a stable, smooth tear film to maintain a clear visual surface. The tear film is a three-layered structure—oil, water, and mucus—that must be perfectly balanced to ensure light passes through cleanly. When the tear film is inadequate, unstable, or evaporates too quickly, dry spots can form on the corneal surface.
This patchy surface acts like an uneven lens, scattering light rays as they enter the eye. This leads to glare, streaks, and fluctuating vision that often improves with a blink. Since the pupil dilates at night, the effects of this unstable surface are magnified, making nighttime driving difficult.
Internal Structural Conditions
When streaking and glare are not due to surface or common refractive issues, the cause may lie in structural changes deeper within the eye, specifically involving the lens or the vitreous gel. These internal changes can scatter light significantly, resulting in more pronounced visual disturbances.
Cataracts
Cataracts involve the clouding of the eye’s natural lens, which sits directly behind the iris and pupil. Normally, the lens is transparent and focuses light sharply onto the retina, but as a cataract develops, proteins in the lens clump together, creating an opacity. This clouding causes light to scatter widely as it passes through, producing severe starbursts, halos, and glare, often worsening gradually over time.
Glaucoma and Ocular Hypertension
Glaucoma, particularly the acute angle-closure form, can sometimes cause the perception of halos or rainbow-colored rings around lights. This symptom is typically related to a sudden, rapid increase in intraocular pressure (IOP), which can cause temporary swelling or edema in the cornea. The swelling distorts the cornea’s structure, leading to the light scattering phenomenon.
Post-Surgical Effects
Patients who have undergone refractive surgeries, such as LASIK, may experience temporary or permanent streaks and glare around lights. This is often a result of corneal edema (swelling) that occurs as a normal part of the healing process. Changes to the cornea’s shape can also induce higher-order aberrations, which are complex focusing errors that manifest as starbursts or halos, especially when the pupil is large in low-light conditions.
When to Consult a Vision Specialist
While many causes of light streaking are manageable, certain symptoms are red flags that warrant immediate professional attention. Any sudden onset of new or significantly increased streaks, flashes of light, or floaters should prompt an urgent visit to an eye doctor. These specific light flashes can be a sign that the vitreous gel is pulling on the retina, which may indicate a retinal tear or detachment.
You should also seek prompt evaluation if the streaking is accompanied by severe eye pain, nausea, vomiting, or a noticeable shadow blocking vision. During an examination, a specialist will perform a comprehensive eye health assessment. This assessment includes checking intraocular pressure and a dilated exam to fully inspect the retina and internal structures to diagnose the cause.