Seeing radiating spikes of light around a point sources, often called starbursts, glare, or halos, is a common visual phenomenon when looking at streetlights or headlights in the dark. This effect can be distracting and sometimes interfere with night driving. While starbursts can be a normal consequence of the eye’s anatomy functioning in low light, they can also signal an underlying issue with the eye’s structure or health. Understanding the causes, which range from basic optical physics to specific eye conditions, helps determine if the symptom requires professional attention.
How Light Scatter Creates Starbursts
The fundamental reason starbursts appear at night relates to how the eye handles light in dark conditions. When ambient light is low, the pupil naturally dilates (mydriasis) to allow maximum light entry into the eye, causing light to enter through the peripheral edges. The edges of the eye’s optical surfaces are not perfectly uniform, introducing minor imperfections called higher-order aberrations. During the day, small pupils block these imperfections and focus light precisely. In the dark, the widened aperture allows light to hit these irregularities, causing it to scatter and diffract internally, which is perceived as the characteristic starburst pattern on the retina.
Common Causes Related to Eye Shape and Surface
Starbursts are often amplified by common structural irregularities in the eye’s shape or surface quality. A frequent cause is astigmatism, a refractive error where the cornea or lens is curved more like a football than a perfectly spherical baseball. This irregular shape causes incoming light rays to be focused unevenly, which drastically exaggerates the light streaking phenomenon, especially when the pupil is dilated at night.
Dry Eye Syndrome is a common cause where the tear film on the corneal surface is compromised. A healthy tear film provides a smooth, uniform surface for light to pass through. However, an uneven or compromised film scatters light upon entry. This surface irregularity creates the visual distortion perceived as starbursts or glare, which can often be managed with lubricating eye drops.
Individuals who wear contact lenses may experience starbursts if the lenses are dirty, scratched, or improperly fitted. The presence of debris or microscopic scratches on the lens surface introduces new points of light scatter. Moreover, ill-fitting lenses can alter the smooth curvature of the eye, contributing to increased optical aberrations.
Vision Conditions Requiring Medical Intervention
The appearance of starbursts can signal a medical condition affecting the clarity of the eye’s components. Cataracts, which involve the clouding of the eye’s natural lens, are a major cause of increased glare and starbursts. The opaque proteins within the lens scatter light internally, increasing dazzling effects and often making night driving difficult.
Corneal surgeries, such as LASIK or PRK, can temporarily or sometimes permanently increase the perception of starbursts. While these procedures correct central vision, the reshaping of the cornea can create a zone where the treated area meets the untreated peripheral cornea. If the pupil dilates wider than the treated zone in the dark, light passing through this transition area can be scattered, causing night vision symptoms.
Other conditions involve the compromise of the cornea’s shape or clarity. Keratoconus is a disease where the cornea thins and bulges into a cone-like shape, leading to irregular light distortion and asymmetrical starbursts. Fuchs’ dystrophy, a genetic condition causing the cornea to swell, also compromises corneal clarity, resulting in light scattering and blurry vision, particularly in the mornings.
Next Steps and When to Seek Help
While mild, occasional starbursts can be a normal part of seeing in low light, the symptom warrants a comprehensive eye examination if it appears suddenly, worsens rapidly, or is accompanied by other symptoms like pain, blurred central vision, or flashing lights. The severity of the visual disturbance is also a factor, particularly if the starbursts interfere with the ability to perform daily tasks like driving safely at night.
An eye care professional can diagnose the underlying cause, which may range from a simple need for an updated eyeglass prescription to the presence of cataracts. Management strategies can include:
- Anti-reflective coatings on glasses to reduce glare.
- Prescription changes to correct unmanaged astigmatism.
- Specific lubricating drops for dry eye.
- Surgical evaluation to replace the cloudy lens for advanced cataracts.