Looking at your Christmas tree can help you figure out if you have a common vision disorder

Staring at your Christmas tree can help diagnose a common vision problem.

If the lights look more like stripes or beams than individual spots, it could indicate astigmatism, which is very common: About 33 percent of Americans suffer from it.

Symptoms of the condition include: blurred vision, headaches and eyestrain, especially after prolonged periods of concentration, such as computer use.

Astigmatism occurs when the clear lens around the eyeball takes on an irregular oval shape instead of the typical perfect roundness.

The football-like shape causes light to focus unevenly on the retina, leading to blurred or distorted vision.

Thanks to the perfectly round shape, the light rays are sharply focused on the retina, so you can see clearly.

With astigmatism, light does not bend evenly as it enters the eye, causing it to focus in multiple places rather than directly on the retina. This leads to blurred vision, both near and far.

Dr. Jennifer Stone, an optometrist based in Baltimore, told Health magazine that the glare from Christmas lights “can disrupt the sharp details of their vision and affect both distant and nearby objects.”

An oval-shaped lens or cornea is largely determined by genetics.

Astigmatism generally runs in families. If one or both parents have astigmatism, their children are also more likely to develop it.

But in some cases, astigmatism can develop later in life due to injury, illness, or age.

There are several tests you can do at home that can strongly indicate the presence of astigmatism.

For example, the astigmatism map test, also called the “astigmatism fan” test, is a simple method to check for possible signs of astigmatism at home.

First, print an astigmatism diagram, which usually shows lines or circles radiating from a central point.

Hold the card at a comfortable distance and cover one eye at a time.

As you focus on the lines, notice any lines that appear brighter or darker than others, or any lines that appear blurred or distorted.

If you notice these irregularities it may indicate the presence of astigmatism, but it is important to remember that this is not a definitive diagnosis. That must be determined by a doctor.

With astigmatism, light does not bend evenly as it enters the eye, causing it to focus in multiple places rather than directly on the retina

Astigmatism is measured in diopters, such as -1.00 or -2.00, to indicate how uneven the curve of your eye is. The higher the number, the more correction you need to properly focus the light.

Dr. Jennifer Tsai, an ophthalmologist from New York City, demonstrated in a video how someone with varying levels of astigmatism would see when staring at their Christmas tree.

The lights become increasingly blurry and brighter as the numbers increase, from -1.00 and higher.

The higher the number, the blurrier your vision becomes without correction because the irregular curve in the eye is more severe.

Astigmatism is measured in diopters, such as -1.00, -2.00, -3.00 and higher, to indicate how uneven the curve of your eye is. The higher the number, the more correction you need to properly focus the light

And astigmatism is especially dangerous when driving at night.

Like the lights of a Christmas tree, the lights of oncoming cars extend and fade to the point where they almost blind the driver to other cars, wrapping them in a halo of light.

Driving can be dangerous for reasons other than the bright light of the headlights. For example, people driving through streets lit with lawn decorations and lights can make it more difficult to see traffic lights and signs.

Wet roads can make this worse by creating reflections, distorting vision and increasing glare.

Some people may experience the symptoms of astigmatism without realizing they have it.

Common symptoms include eye strain or discomfort, eye pain, blurred or distorted vision, headaches, fatigue, trouble seeing at night, and frequent squinting to see clearly.

If you notice these symptoms, a visit to an ophthalmologist can help you diagnose and address the problem.

The condition can be treated in some cases with glasses, contact lenses or laser surgery.