Seeing light streaks, starbursts, or halos around bright lights is a common visual experience, often startling when driving at night. These phenomena, known clinically as photopsia or glare, occur when light is scattered or diffracted incorrectly within the eye. While this visual distortion can be a harmless result of normal optics, it may also signal an underlying structural change requiring professional evaluation. Understanding the source of these light streaks helps determine if the cause is a simple refractive error or a condition needing prompt medical attention.
Common Optical Causes of Streaks and Glare
The most frequent cause of light streaks involves how light physically bends, or refracts, upon entering the eye. Astigmatism, a common refractive error, is a prime example where the cornea or lens is shaped more like a football than a perfect sphere. This irregular curvature causes light to focus on multiple points instead of a single, sharp point on the retina. This results in the characteristic stretching of light into streaks or starbursts, particularly noticeable around point sources of light.
Visual disturbances are often heightened at night because the pupil naturally dilates in low light to let in more illumination. When the pupil is larger, light passes through the peripheral edges of the lens. Minor imperfections there can cause greater scattering of light, which is perceived as increased glare or halos around streetlights and oncoming headlights.
A disruption to the tear film, such as from dry eyes or contact lens wear, can also be a temporary cause of light scatter. The cornea relies on a smooth, continuous layer of tears for clear vision. Any unevenness on the eye’s surface will immediately scatter incoming light, though blinking typically resolves this issue by restoring the smooth tear film layer.
Light streaks can also occur following procedures that alter the eye’s front surface. After refractive surgeries like LASIK, changes to the corneal curvature may temporarily or permanently induce higher-order aberrations, manifesting as increased starbursts or glare. Even after cataract surgery, some patients experience temporary glare or halos as the brain adjusts to the new intraocular lens.
Vision Changes Due to Structural Eye Conditions
Structural changes within the eye’s internal components are a significant source of light distortion. Cataracts, the progressive clouding of the eye’s natural lens, are one of the most common conditions causing halos and streaks. Proteins within the lens break down and clump together, scattering light internally before it reaches the retina. This scattering effect creates the sensation of glare and light streaks, often severely degrading night vision.
The cornea, the clear front dome of the eye, can also develop structural issues that scatter light. Corneal edema, or swelling, disrupts the precise arrangement of the corneal tissue, causing light to scatter upon entry. This can occur due to conditions like Fuchs’ dystrophy or prolonged contact lens wear, leading to hazy vision often accompanied by glare.
Inflammation within the eye, known as uveitis, can lead to the accumulation of inflammatory cells and debris in the gel-like substance that fills the eye. This debris, often perceived as floaters, interferes with the light pathway, causing light sensitivity, blurred vision, and the perception of light streaks. The location of the inflammation determines the specific nature of the visual disturbance.
Sudden Streaks and Flashes Requiring Immediate Attention
A sudden onset of flashes or streaks, especially when accompanied by new floaters, should be treated as a medical urgency. These symptoms, known as photopsia, frequently signal an issue with the retina, the light-sensitive tissue lining the back of the eye. They are caused by the vitreous gel, which fills the eyeball, beginning to shrink and pull away from the retina.
This pulling action is called vitreous traction. The physical stimulation of the retina is what the brain interprets as a sudden burst of light or a lightning streak. If the vitreous gel pulls too strongly, it can create a retinal tear, which may quickly progress to a retinal detachment. A retinal detachment requires immediate treatment to prevent permanent vision loss.
Visual disturbances can also originate in the brain rather than the eye itself, such as with a migraine aura. Migraine-related visual phenomena are described as shimmering, expanding, zigzag lines or arcs of light. Unlike retinal flashes, which usually occur in one eye and appear as brief streaks, a migraine aura typically affects both eyes and lasts for several minutes.
Any sudden appearance of flashes, streaks, or a shadow resembling a curtain or veil descending over the vision demands immediate ophthalmological consultation. While temporary visual changes like a migraine aura are harmless, distinguishing them from a retinal tear or detachment is impossible without a comprehensive eye examination. Prompt action is necessary to preserve vision in the event of a retinal emergency.