Strings of lights on rooftops, a lit tree in the window, and car headlights on a rainy night. This time of year, many people notice that bright points of light look like little stars or have soft rings around them. Some of that is normal optics. Some of it is a clue that your eyes need a checkup. Here is how the eye focuses, and why night changes the picture.
How light gets focused
The American Academy of Ophthalmology (AAO) explains that light first passes through the cornea, the clear, dome-shaped front of the eye, which does much of the focusing. Behind it, the colored iris surrounds the pupil. Muscles in the iris widen or narrow the pupil to control how much light gets in. Directly behind the pupil is the lens, which fine-tunes focus and changes shape to help you see up close. The focused light then lands on the retina, where the macula provides sharp central vision.
What happens at night
In dim light, the pupil opens wide to let more light in. That means light passes through a larger area of the cornea and lens, including the outer edges. Any small irregularity in the tear film, cornea or lens has more effect when the pupil is large. The result can be starbursts, streaks or halos around bright lights that you barely notice in daylight.
Common reasons lights look worse
- Dry eye. An uneven tear film scatters light. Blinking or artificial tears may sharpen things for a moment.
- Cataracts. As the lens clouds with age, it scatters light and glare increases.
- An outdated glasses prescription, including small amounts of astigmatism.
- Smudged or scratched glasses and dirty windshields.
When to get it checked
If halos or glare are new, getting worse, or making night driving harder, see an eye doctor. Sudden halos with eye pain, redness, headache or nausea need urgent care, because they can signal a rapid rise in eye pressure.
Questions? Call our Westlake Village office at (805) 230-2126.
I enjoy the holiday lights as much as anyone. If they have started to look like fireworks every night, though, it is worth finding out why.
Source: Eye Anatomy: Parts of the Eye and How We See (American Academy of Ophthalmology). This article is an educational summary written by Khanna Vision Institute and is not a substitute for medical advice.