Seeing lights appear blurry, surrounded by glowing rings (halos), or radiating spikes (starbursts) is a common visual experience, particularly noticeable at night. This phenomenon occurs when light entering the eye is scattered instead of being precisely focused onto the retina, the light-sensitive tissue at the back of the eye. While often simply a sign of a common refractive error, these visual disturbances can also indicate underlying changes in the eye’s physical structure or health. Understanding the causes behind this light distortion is key to restoring clear vision.
The Optics of Light Scattering
The eye’s optical system is designed to bend, or refract, light rays through the clear outer layer (the cornea) and an internal focusing structure (the lens). Ideally, these structures work together to converge all incoming light to a single, sharp focal point on the retina. Blurry light occurs when this focus is disrupted, causing the light to spread out or scatter.
This scattering is often magnified in low-light conditions because the pupil, the eye’s aperture, naturally dilates to let in more light. A wider pupil allows light rays to enter through the peripheral edges of the cornea and lens, where optical imperfections are more pronounced. These imperfections scatter the light, creating the characteristic halos and starbursts that affect night vision and reduce contrast.
Common Causes Related to Refractive Errors
The most frequent source of blurry lights is a refractive error, meaning the eye is not the correct shape to bend light accurately. Astigmatism is a common culprit, occurring when the cornea or lens is curved like a football instead of a basketball. This uneven curvature causes light to focus on multiple points instead of one, resulting in streaky, starburst patterns radiating from light sources. Astigmatism is a common condition, affecting about one in three people in the United States.
Myopia, or nearsightedness, occurs when the eye is too long, causing light to focus in front of the retina. While this primarily makes distant objects blurry, the unfocused light can also create halos around bright sources. Changes in the eye’s shape due to aging, known as presbyopia, can also contribute to blurriness and difficulty focusing. Furthermore, the need for an updated prescription for glasses or contact lenses can lead to noticeable light scattering if current lenses no longer compensate for the eye’s specific refractive needs.
Underlying Medical Conditions and Eye Health
Beyond refractive errors, several medical conditions can cause light to scatter and appear blurry. Cataracts are a leading cause, involving the progressive clouding of the eye’s natural lens, often due to aging. Crystalline proteins within the lens clump together, forming opacities that scatter light and create intense glare and halos around lights. This effect is often worse with posterior subcapsular cataracts.
Dry Eye Syndrome can compromise vision clarity by creating an irregular surface on the cornea. A healthy tear film ensures a smooth front surface for light entry, but a compromised film breaks up quickly, causing surface roughness that scatters light until a blink restores the film. Glaucoma can damage the optic nerve, but in its acute form, increased pressure can cause the cornea to swell, leading to halos and blurry vision that require immediate medical attention. Systemic diseases like diabetes can also affect vision, causing fluctuating focus and increasing the risk of early cataracts and dry eye, all contributing to light scatter.
Diagnosis and Treatment Options
A comprehensive eye examination is necessary to accurately diagnose the cause of blurry lights and visual halos. During this assessment, an eye care professional performs a visual acuity test to measure sharpness and uses a slit-lamp examination to view the cornea and lens in high magnification. This process allows the doctor to identify subtle issues like corneal surface irregularity from dry eye or the early clouding of a cataract.
Treatment is tailored directly to the underlying cause of the light scatter. For refractive errors, the solution is often corrective lenses, such as glasses with anti-reflective coatings or toric contact lenses that counteract the uneven curve of astigmatism. When dry eye is the issue, treatment may involve lubricating drops or prescription eye drops that reduce inflammation or increase tear production. For conditions like cataracts, where the lens is significantly clouded, the definitive treatment is surgical replacement of the natural lens with a clear artificial intraocular lens.