Why Do I See Halos Around Lights at Night?

You are driving home after dark when you notice that every streetlight and oncoming headlight seems surrounded by a bright, glowing ring. It may look like a soft haze or a distinct circle of light radiating outward from the source. These visual disturbances are called halos, and they are one of the most common reasons patients schedule an appointment at Soni Vision Institute. While halos are not always a sign of a serious problem, they can sometimes indicate a condition that needs prompt attention. Understanding what causes them, and when they warrant an evaluation, can help you protect your vision.

What Are Halos, Exactly?

Halos are bright circles or rings that appear to surround a light source, particularly in dim or dark environments. They occur because of light diffraction, a phenomenon where light waves bend as they pass through or around structures in the eye. Under normal conditions, the cornea and crystalline lens work together to focus light precisely onto the retina. When something disrupts that process, whether it is a change in the lens, the corneal surface, or the tear film, light scatters instead of focusing to a single point. The result is a visible ring or glow around lights.

Halos are most noticeable at night or in low-light conditions because the pupil dilates in darkness, allowing more light to enter the eye and pass through areas that may be irregular or clouded. During the day, when the pupil is smaller, less of the imperfect optical surface is exposed and halos are far less apparent.

Common Causes of Halos Around Lights

There are several reasons you might be seeing halos. Some are benign and easily corrected, while others may require medical or surgical treatment. Here are the most common causes:

Cataracts

Cataracts are the most common cause of halos in adults over 50. As the natural lens inside the eye gradually becomes cloudy, it scatters incoming light rather than focusing it cleanly. This produces halos, starbursts, and glare, especially when looking at bright lights against a dark background. In fact, halos around headlights while driving at night are often the very first symptom that brings cataract patients to our practice. Many patients do not realize how much their lens has changed until they describe these nighttime visual disturbances during an exam.

As cataracts progress, halos tend to become more pronounced and can be accompanied by blurred vision, faded colors, and difficulty with contrast. If cataracts are the cause, the definitive treatment is cataract surgery, which replaces the clouded lens with a clear artificial lens implant. Most patients notice a dramatic improvement in nighttime vision after surgery.

Glaucoma and Elevated Eye Pressure

Glaucoma can cause halos, particularly when intraocular pressure (IOP) is elevated. High eye pressure can cause swelling of the cornea (corneal edema), which disrupts the smooth optical surface and scatters light. In chronic open-angle glaucoma, halos may come and go or gradually worsen. In acute angle-closure glaucoma, halos can appear suddenly and are typically accompanied by severe eye pain, headache, nausea, and a rapid decline in vision. This is a medical emergency that requires immediate treatment to prevent permanent vision loss.

Corneal Conditions

The cornea is the clear front surface of the eye and is responsible for roughly two-thirds of the eye's focusing power. Any condition that affects corneal clarity or shape can cause halos. Corneal edema, which is swelling of the cornea from fluid buildup, is a common culprit. Fuchs endothelial dystrophy, a condition where the cells that pump fluid out of the cornea gradually deteriorate, often causes halos and blurred vision that are worse upon waking and may improve as the day goes on. Corneal scarring from injury or infection, keratoconus (a progressive thinning and bulging of the cornea), and other corneal dystrophies can also scatter light and produce halos.

Uncorrected Refractive Errors

If your glasses or contact lens prescription is out of date, or if you have an uncorrected refractive error such as myopia (nearsightedness), hyperopia (farsightedness), or astigmatism, light may not focus properly on the retina. This can produce mild halos, especially in low-light conditions when the pupil is dilated. The fix is often as straightforward as an updated prescription.

Dry Eye

Dry eye is an underappreciated cause of halos and glare. The tear film is the first refractive surface that light encounters as it enters the eye. When the tear film is unstable, thin, or breaks up quickly between blinks, it creates an irregular optical surface that scatters light. Patients with dry eye often notice halos that seem to fluctuate, sometimes improving right after a blink and worsening a few seconds later. Treating the underlying dry eye, whether through artificial tears, prescription drops, or other therapies, can significantly reduce these symptoms.

After LASIK or PRK

Halos are a well-known side effect in the early weeks and months following LASIK or PRK surgery. During the healing process, the reshaped corneal surface may temporarily scatter light, particularly in dim conditions. The vast majority of patients see these symptoms resolve within three to six months as the cornea heals and stabilizes. In rare cases, halos may persist longer, particularly in patients with large pupils or higher prescriptions. Modern laser platforms with wavefront-guided and topography-guided treatments have significantly reduced the incidence of lasting halos after refractive surgery.

When Halos Are a Medical Emergency

Most causes of halos develop gradually and are not immediately dangerous. However, there is one scenario where halos require emergency care: acute angle-closure glaucoma. If you experience the sudden onset of halos around lights along with any of the following symptoms, seek medical attention immediately:

• Severe eye pain that comes on rapidly
• Headache, particularly on the same side as the affected eye
• Nausea or vomiting
• A red, inflamed eye
• Sudden blurred or foggy vision
• Seeing rainbow-colored rings around lights

In acute angle-closure glaucoma, the drainage angle of the eye closes suddenly, causing a rapid spike in eye pressure. Without prompt treatment, the optic nerve can sustain permanent damage within hours. This is a true ocular emergency. If you experience these symptoms, go to the nearest emergency room or call your ophthalmologist immediately.

How Halos Are Diagnosed

Determining the cause of halos requires a comprehensive eye examination. At Soni Vision Institute, the evaluation typically includes several key components:

Visual Acuity and Refraction

Testing your vision at distance and near, and checking whether an updated prescription improves your symptoms. This helps rule out or confirm uncorrected refractive error as a contributing factor.

Slit-Lamp Examination

A slit-lamp biomicroscope allows your ophthalmologist to examine the structures of the eye at high magnification. This is essential for evaluating the cornea for edema, scarring, or dystrophy, and for examining the crystalline lens for cataract changes. The slit lamp can also reveal signs of inflammation or other abnormalities that may be causing light scatter.

Tonometry

Measuring the pressure inside the eye is a critical part of any evaluation for halos. Elevated intraocular pressure can indicate glaucoma and can directly cause corneal edema and halos. Tonometry is quick, painless, and performed during a routine office visit.

Corneal Topography

This imaging test creates a detailed map of the corneal surface, measuring its curvature and identifying irregularities. It is particularly useful for diagnosing conditions like keratoconus or evaluating the cornea after refractive surgery. Corneal topography can reveal subtle surface changes that are not visible on a standard exam but may be significant enough to cause halos.

Tear Film Assessment

If dry eye is suspected, your ophthalmologist may evaluate the quality and stability of your tear film using specialized dyes and imaging. Tear breakup time, corneal staining patterns, and meibomian gland assessment can all help determine whether an unstable tear film is contributing to your symptoms.

Treatment Depends on the Cause

Because halos are a symptom rather than a disease, the treatment approach depends entirely on the underlying cause. Here is a general overview:

• Cataracts: Updated glasses may help temporarily, but cataract surgery is the definitive solution. Modern cataract surgery replaces the cloudy lens with a clear implant, and most patients notice a significant improvement in nighttime glare and halos.
• Glaucoma: Treatment focuses on lowering eye pressure through medications, laser procedures, or surgery. Managing the pressure resolves the corneal edema that produces halos.
• Corneal conditions: Treatment varies depending on the specific diagnosis. Options may include hypertonic saline drops for Fuchs dystrophy, specialized contact lenses for keratoconus, or in advanced cases, corneal transplant surgery.
• Refractive errors: An updated glasses or contact lens prescription can resolve halos caused by uncorrected vision.
• Dry eye: A tailored treatment plan that may include artificial tears, anti-inflammatory drops, warm compresses, or other therapies to restore a healthy tear film.
• Post-refractive surgery halos: These typically resolve on their own during the healing process. In the interim, your surgeon may recommend lubricating drops and nighttime driving precautions.

When to See an Ophthalmologist

You should schedule an eye exam if you are experiencing halos around lights, especially if they are new, worsening, or affecting your ability to drive safely at night. While halos are sometimes caused by something as simple as an outdated prescription or dry eyes, they can also be an early sign of cataracts, glaucoma, or a corneal condition that benefits from early detection and treatment.

As a general guideline, consider seeing an ophthalmologist if:

• Halos are new or have recently become more noticeable
• They are accompanied by blurred vision, eye pain, or headaches
• You have difficulty driving at night because of glare
• You have a family history of glaucoma or cataracts
• It has been more than a year since your last comprehensive eye exam

At Soni Vision Institute, Dr. Soni and Dr. Reddy perform thorough evaluations to identify the cause of your symptoms and develop a personalized treatment plan. If you are noticing halos or glare, the sooner you are evaluated, the more options you have. Schedule a consultation to get the answers you need.

Sources

1. American Academy of Ophthalmology. "Halos." EyeWiki. eyewiki.aao.org/Halos.
2. Puell MC, Palomo-Alvarez C, Barrio AR, Goméz-Sanz FJ, Pérez-Carrasco MJ. "Relationship between halo size and forward light scatter." British Journal of Ophthalmology. 2014;98(10):1389–1392. doi:10.1136/bjophthalmol-2014-304872.
3. American Academy of Ophthalmology. "What Are Cataracts?" aao.org.
4. American Academy of Ophthalmology. "What Is Glaucoma?" aao.org.