Halos Around Lights: Causes, What's Normal and When to See a Doctor

You notice it first while driving at night: rings around every streetlight and headlight. The question that follows is almost always the same one: is this normal, or is something wrong?

Key Takeaway

Some halos around lights are normal, particularly at night around bright light sources. Halos become a medical concern when they are new, worsening, affect one eye, or come with pain. Coloured or rainbow halos together with severe eye pain, redness, headache or nausea need same-day emergency care; that combination can indicate a sudden rise in eye pressure.

Are Halos Around Lights Normal?

Often, yes, and this is worth establishing before anything else.

A degree of halo and glare around bright lights at night is normal in healthy eyes. In the dark your pupil widens to let more light in, and a wider pupil uses more of the outer edge of your natural lens and cornea, where light is focused slightly less precisely. Younger people and people with naturally large pupils notice it more.

If you have always seen a faint ring around streetlights, and it has not changed, that is very likely how your eyes have always worked.

What is not normal is change. Halos matter when they are:

• New, or clearly worse than before
• Present in only one eye
• Getting worse over weeks or months
• Accompanied by pain, redness, headache or nausea
• Accompanied by blurred vision that does not clear
• Making night driving genuinely difficult

The rest of this article is about telling those apart.

The One Combination That Needs Same-Day Care

Most causes of halos can wait for a routine appointment. One cannot.

Seek emergency eye care the same day if you have coloured or rainbow halos along with any of the following:

• Severe pain in or around one eye
• A red eye
• Headache, often on the same side
• Nausea or vomiting
• Blurred or rapidly dimming vision
• A pupil that looks larger than the other and does not react

This combination can indicate a sudden blockage of the eye’s drainage system, causing pressure inside the eye to rise quickly. The cornea swells with fluid, and that swelling is what scatters light into coloured rings. It is a recognised ophthalmic emergency, because vision can be lost quickly without treatment. It is one of the conditions covered under angle-closure glaucoma.

There is a trap here worth knowing about. The nausea, vomiting and headache can be severe enough that people are assessed for a stomach upset or a neurological problem while the eye goes unexamined. If you have these symptoms together with eye pain or visual change, say so clearly, and ask for the eye to be looked at.

This presentation is not common. But it is the reason a symptom as ordinary as halos deserves an article that starts here rather than ending here.

Why Halos Happen in the First Place

Light reaching your retina passes through the tear film, the cornea, the pupil and the lens. Each of those needs to be clear and smooth for light to arrive as a sharp point.

When any of them becomes cloudy, swollen, uneven or irregular, some light scatters instead of focusing. Around a bright source against a dark background, that scattered light spreads out into a visible ring.

Which structure is scattering the light determines the cause and how urgent it is.

Common Causes of Halos Around Lights

Cataract

This is the commonest explanation in adults over 50, and often the first symptom people notice.

As the natural lens clouds, light scatters as it passes through. Halos and glare around headlights at night usually appear before daytime vision is noticeably affected, which is why night driving is often the first thing to become difficult.

Cataract halos build gradually over months or years, affect both eyes at different rates, and come without pain. Surgery is considered when the change starts to interfere with daily life, and a cataract assessment will identify how far it has progressed.

Dry eye and an unstable tear film

Frequently overlooked, and very common.

Your tear film is the first surface light meets. When it is thin or breaks up quickly between blinks, the surface becomes uneven and scatters light. The giveaway is that the halos fluctuate worse when you have been on a screen, in air conditioning or in the wind, and briefly better right after you blink.

If your vision clears momentarily when you blink hard, dry eye is a strong candidate. It is also one of the more treatable causes.

Corneal swelling or scarring

The cornea is the clear window at the front of the eye. Anything that makes it swell or lose transparency will scatter light.

This can follow contact lens overwear, corneal infection or injury, certain inherited corneal conditions, or eye surgery. Corneal swelling from any cause tends to produce halos that are worse on waking and improve through the morning.

After LASIK, SMILE or ICL

Halos, glare and starbursts at night are a recognised part of recovery from laser vision correction and from lens-based procedures such as ICL.

They occur because the treated zone of the cornea, or the optic of an implanted lens, has an edge, and at night, when the pupil widens beyond it, light passing the transition scatters.

For most people these settle substantially as the eye heals and the brain adapts, though the timeline varies between individuals and procedures. Two practical points:

• Report them at your follow-up visits rather than waiting to see if they pass. Your surgeon needs to know.
• Ask about them beforehand if you are still deciding. Night vision effects are a known consideration in choosing between refractive procedures, and pupil size is one of the things assessed during your suitability workup.

New halos appearing long after an uneventful recovery are a different matter and should be examined.

After cataract surgery with a multifocal lens

Multifocal and extended-depth-of-focus lens implants split incoming light between different focal distances so that you can see at more than one range without glasses.

That design has a trade-off, and halos and glare at night are the main one. For most people the effect lessens over the following months as the brain adapts. It is discussed as part of the consent process, and if it is troubling you, say so at your follow-up; it is expected, not a complication you should absorb silently.

Uncorrected spectacle power and large pupils

Sometimes the answer is simply the wrong prescription. Uncorrected short-sightedness, and astigmatism in particular, spreads light rather than focusing it, and the effect is exaggerated at night when the pupil is wide.

If your halos improve when you squint, an updated spectacle test is a reasonable first step.

Raised eye pressure

Halos can appear when pressure inside the eye rises enough to make the cornea swell, whether or not there is a sudden attack.

One cause deserves particular mention in India. Long-term use of steroid eye drops often bought without a prescription, or refilled from an old prescription, can raise eye pressure, and patients with steroid-induced pressure rise have presented with dimness of vision and halos. If you use steroid eye drops and have started seeing halos, have your eye pressure checked and mention the drops.

Halos That Come and Go Without Pain

This pattern is specific enough to deserve its own section, and it is the one most likely to be dismissed.

Some people get episodes of blurring and halos, without pain, that resolve on their own, often in the evening, in dim light, or at the cinema. Walking into a brighter room can end the episode, because bright light constricts the pupil and pulls the iris away from the drainage channels.

This can represent intermittent narrowing of the eye’s drainage angle. Attacks typically recur, and each one can do further damage. Because there is no pain and the symptoms resolve, people sometimes wait for years.

If halos come and go in dim light and clear in bright light, arrange an eye examination even though you feel fine between episodes. This is one of the few situations where a symptom that goes away on its own is more concerning rather than less.

Everyday Medicines That Can Trigger an Attack

In an eye with a naturally narrow drainage angle, some medicines widen the pupil enough to block drainage and precipitate an attack. Several are sold over the counter in India.

Reported precipitants include:

• Cold and flu preparations and cough mixtures
• Antihistamines
• Some antidepressants
• Certain drugs for breathing conditions
• Some anti-seizure medicines
• Dilating eye drops used for examination

This is not a reason to avoid these medicines. The great majority of people take them without any eye problem at all.

What it does mean is worth acting on: if you have been told you have narrow angles, or you have a family history of angle-closure glaucoma, mention it to any doctor prescribing for you and to your pharmacist. And if you develop eye pain with halos after starting a new medicine, treat it as urgent.

Your eye specialist assesses the depth of the front chamber of the eye before using dilating drops, for exactly this reason.

Halos, Migraine Aura and Floaters Are Not the Same Thing

These three get confused constantly, and telling them apart helps you describe the problem accurately.

A sudden shower of new floaters, or floaters with flashes of light, needs prompt examination in its own right; that is a different problem from halos.

What Your Eye Specialist Will Check

1. History of when the halos started, whether one eye or both, whether they fluctuate, and any recent surgery, injury, new medicines or eye drops.
2. Vision test, each eye separately.
3. Slit-lamp examination of the tear film, cornea, front chamber and lens; this usually identifies the cause.
4. Eye pressure measurement.
5. Assessment of the drainage angle, if narrow angles are suspected.
6. Dilated retinal examination, where indicated, though this is deferred if the angle is very narrow.
7. Additional imaging or scans, in selected cases.

Most people need only the first four.

When to See a Doctor

Same day, as an emergency:

• Coloured halos with severe eye pain, redness, headache, nausea or vomiting
• Any sudden loss or rapid dimming of vision
• Halos with a fixed, enlarged pupil in one eye

Within days:

• Halos that come and go in dim light and clear in bright light
• New halos in one eye only
• Halos with any eye discomfort, even mild
• New halos after starting a new medicine or eye drop
• New halos long after refractive or cataract surgery

At a routine appointment:

• Gradually increasing halos and night glare over months, in both eyes, without pain
• Halos that fluctuate with screen use and improve on blinking
• Halos during the expected recovery period after refractive surgery; mention them at your scheduled follow-up

If it has been over a year since your last full eye examination, a new symptom is a reasonable prompt to book one.

Conclusion

Halos are one of those symptoms that mean almost nothing on their own and a great deal in combination. On their own, at night, unchanged for years, they are usually just how your eyes handle bright light in the dark.

Three patterns are worth remembering. Coloured halos with pain, redness and nausea means the same day, not next week. Halos that come and go in dim light and clear in bright light means an appointment soon, even though you feel fine in between. And halos that have crept up gradually over months while night driving got harder usually means a cataract which is a fixable problem, not an emergency.

If you are unsure which of those describes you, that uncertainty is itself the reason to book an examination. A slit-lamp check and an eye pressure reading take a few minutes and answer the question properly.