The perception of a ring in your vision, often described as halos around light sources, is a common visual symptom. These phenomena are particularly noticeable at night around streetlights or headlights. They occur because light is being scattered or bent abnormally before it reaches the retina. The causes for seeing these rings range from temporary environmental factors to structural changes within the eye or neurological events. Understanding this light distortion helps determine if a simple adjustment or a medical evaluation is required.
Simple Optical Phenomena
Seeing a temporary ring around a light source is often a simple consequence of light interacting with the eye’s surface. This effect, known as diffraction, involves the slight bending of light waves as they pass around an edge or through a fine opening. Glare from bright lights, such as oncoming car headlights, is a common trigger, especially when the pupil is dilated in low-light conditions.
The tear film, which covers the front surface of the eye, can also create a halo effect when its consistency is uneven. If you have dry eyes, light passing through a disrupted layer of moisture can scatter, producing a temporary halo until tears are redistributed. Similarly, a smudge on eyeglasses or a dirty contact lens can diffract incoming light, creating a visible ring that disappears once cleaned.
Halos and glare are common immediately following refractive surgeries, such as LASIK. This occurs because the procedure changes the shape of the cornea, scattering the light passing through the reshaped tissue. These post-surgical effects are typically temporary and diminish as the eye heals in the weeks following the operation.
Conditions Affecting the Eye’s Lens and Surface
Structural changes to the eye’s internal components can cause light to scatter permanently, leading to persistent halos. The crystalline lens, located behind the iris, is normally transparent and focuses light onto the retina. Cataracts, which involve the progressive clouding of this lens, disrupt its clarity. As the lens proteins clump and become opaque, incoming light is scattered in multiple directions. This diffusion of light is what the eye perceives as a halo or bright ring surrounding a light source.
Disruptions to the cornea, the clear dome at the front of the eye, can also cause light distortion and halos. Corneal edema, or swelling of this tissue, alters the smooth curvature necessary for accurate light refraction. This swelling can be caused by overwearing contact lenses or by conditions like Fuchs’ Dystrophy. The increased fluid in the cornea scatters light, making halos a noticeable symptom, often alongside foggy vision, particularly in the morning.
Visual Disturbances from Migraine Auras
A distinct type of ring or pattern in the vision can signal a neurological event, such as a migraine aura. This visual disturbance, termed a scintillating scotoma, is not caused by light scattering in the eye. Instead, it originates from abnormal electrical activity in the brain’s occipital cortex, which processes vision. Unlike static halos, this phenomenon is a complex, moving, and shimmering visual pattern that often begins as a flickering spot and expands outward in a C-shaped arc.
This arc is frequently described as having jagged, zigzagging lines, which doctors call a fortification spectrum. This term is used because the pattern resembles the walls of a medieval fort. The visual display is temporary, usually lasting between 20 and 60 minutes. It may precede the migraine headache or occur without any headache at all, known as an acephalgic migraine.
The visual disruption represents a slow wave of nerve cell activity that spreads across the visual cortex of the brain. The edge of this wave corresponds to the shimmering, colorful, and moving lines that the person sees. Because the cause is in the brain and not the eye itself, the visual symptoms remain visible even if the person closes their eyes.
Warning Signs and When to Contact a Doctor
While many causes of visual rings are benign, some instances signal serious conditions that require immediate medical attention. The most urgent concern is acute angle-closure glaucoma, a medical emergency characterized by a rapid spike in the fluid pressure inside the eye. This sudden pressure increase compresses the cornea, leading to immediate edema. This results in the appearance of prominent, often rainbow-colored, halos around lights.
This specific type of glaucoma is rarely an isolated visual symptom; it is typically accompanied by severe indicators. Patients often experience intense, sudden eye pain, a throbbing headache, and blurred or decreased vision. Systemic symptoms, which can include nausea and vomiting, are caused by the severe pain and elevated pressure, making this an urgent situation.
Any sudden onset of halos, especially when paired with pain or a noticeable decline in vision, warrants an immediate visit to an emergency room or a call to your ophthalmologist. Other warning signs indicate the need for professional evaluation:
- Persistent halos that do not resolve.
- Eye redness.
- Foreign body sensation.
- Persistent light sensitivity.
A comprehensive eye examination with an eye care professional, such as an optometrist or ophthalmologist, is the definitive way to diagnose the underlying cause. This examination ensures prompt treatment for conditions that threaten vision health.