Astigmatism is a really common vision problem that can cause blurry vision at all distances. So, what causes this condition?
Usually, astigmatism happens when your cornea or lens isn’t perfectly round. Instead, it’s shaped more like a football. This shape makes light bend unevenly when it enters your eye, leading to blurry or distorted vision.
This article will dive into how astigmatism affects vision, what causes it, how doctors diagnose it, and what treatment options are available.
What is astigmatism? Defining the condition
To understand how astigmatism affects vision, it helps to know how the eye normally works. In a person with typical vision, light enters the eye and focuses directly on the retina, the light-sensitive tissue at the back of the eye. This creates a clear image that’s sent to the brain.
In a person with astigmatism, the light rays don’t bend correctly when they pass through the cornea, resulting in blurry vision. The irregular shape of the cornea (or sometimes the lens) keeps light from focusing correctly on the retina.
Astigmatism is considered a refractive error, like nearsightedness and farsightedness. In fact, it’s common for astigmatism to occur along with other refractive errors.
Types of Astigmatism: A Closer Look
Astigmatism comes in different forms, depending on what’s causing the blurry images.
Corneal vs. Lenticular Astigmatism
Corneal astigmatism is caused by a cornea that’s shaped irregularly. Instead of being shaped like a round ball, it’s shaped more like a football.
Lenticular astigmatism happens when the lens inside your eye is misshapen.
Types of Astigmatism: Based on Corneal Shape
Astigmatism is also classified by the direction of the irregular curve in the cornea.
- With-the-rule astigmatism means the steepest curve is vertical.
- Against-the-rule astigmatism means the steepest curve is horizontal.
- Oblique astigmatism means the steepest curve is at an angle.
How does astigmatism affect vision?
When you have astigmatism, your vision will likely be blurry whether you’re looking at something close up or far away. People with normal vision can see clearly and in focus no matter the distance.
Visual distortions caused by astigmatism
Astigmatism can cause all sorts of visual quirks, including:
- Blurry vision
- Streaks in your field of vision
- Glare
- Shadows around objects
- Halos around lights
Impact on night vision
Astigmatism can really throw off your night vision. It reduces contrast sensitivity, which makes it hard to see well in low-light situations. Driving at night can be especially difficult when you have uncorrected astigmatism.
What causes astigmatism?
In many cases, experts don’t know exactly what causes astigmatism.
However, they have identified some potential causes:
- Genetics
- Eye injuries
- Eye diseases
- Complications following eye surgery
It’s worth noting that some common myths about astigmatism aren’t supported by evidence. For instance, reading in dim light or sitting close to the television or computer screen doesn’t cause astigmatism or make it worse.
Recognizing the Signs: Symptoms of Astigmatism
Astigmatism symptoms can range from mild to severe, depending on the degree of the refractive error. You might have astigmatism if you’ve experienced the following:
- Blurry vision at all distances
- Eye strain and fatigue
- Frequent headaches
- Squinting to see clearly
- General eye discomfort or irritation
If you have any of these symptoms, you should consult an eye care professional for a comprehensive eye exam.
How is astigmatism diagnosed?
Experts recommend that children have their eyes checked early and often. Many vision problems are easier to correct when caught early.
To diagnose astigmatism, an eye doctor will typically use one or more of the following tests:
- Visual acuity test: This is the standard eye chart test that measures how well you can see at various distances.
- Keratometry: This test measures the curvature of your cornea.
- Corneal topography: This creates a detailed map of the surface of your cornea.
- Phoropters and autorefractors: These instruments help determine your exact prescription.
Correcting astigmatism: Treatment options
Fortunately, there are several ways to correct astigmatism and improve your vision.
Eyeglasses and contact lenses
Eyeglasses with specially ground lenses can compensate for the uneven curvature of your cornea or lens, allowing light to focus correctly on your retina. Your ophthalmologist or optometrist can prescribe lenses that correct your specific type and degree of astigmatism.
There are also several types of contact lenses that can correct astigmatism. Toric contact lenses are designed specifically for astigmatism. Another option is rigid gas permeable (RGP) lenses, which can sometimes provide sharper vision than soft lenses.
Orthokeratology (Ortho-K)
Orthokeratology involves wearing special rigid contact lenses overnight to temporarily reshape your cornea. You’d remove the lenses during the day, and, for a while, your vision would be clearer. This isn’t a permanent fix, though; you’d have to continue wearing the lenses regularly to maintain the effect.
Refractive surgery
Refractive surgery options like LASIK, PRK, and LASEK can permanently correct astigmatism by reshaping your cornea. These procedures use lasers to precisely remove tissue and create a more even surface.
Understanding your prescription
Astigmatism is measured in diopters, and most people have some degree of it. A perfectly spherical eye would have 0 diopters. Most people fall in the range of 0.5 to 0.75 diopters. If your astigmatism measures 1.5 diopters or higher, you probably need corrective lenses.
An astigmatism prescription will include three numbers: spherical, cylinder, and axis. Your doctor uses these numbers to create lenses that correct your vision.
Conclusion
Astigmatism happens when the cornea or lens of your eye isn’t perfectly round. This can cause blurry or distorted vision at any distance. A comprehensive eye exam can diagnose astigmatism, and most cases can be treated with glasses, contacts, or even surgery. Make sure you see your eye doctor regularly to keep your vision as sharp as possible.