What are the differences between astigmatism and myopia?

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Astigmatism happens when the cornea (the clear front layer of the eye) or the lens (an inner part of the eye that helps with focus) has a different shape than usual. This can affect vision and make things appear blurry.

Myopia, or nearsightedness, is when a person cannot clearly see far-away objects. It occurs when the shape of the eye causes light to bend differently as it enters the eye.

Both astigmatism and myopia are known as refractive errors. This term refers to a type of vision issue that can make it difficult to see clearly.

In fact, refractive errors are the most common type of vision concern. They occur when the shape of the eye prevents light from focusing correctly on the retina, which is a light-sensitive layer of tissue in the back of the eye.

While both conditions are similar and can affect vision, they are distinct visual issues. Some key differences include:

• Eye shape: Both conditions occur when the eye has a different shape than usual. However, the shape differs for both conditions. Astigmatism occurs due to the cornea or lens having a different shape. Often the cornea may have more of a football shape, rather than being round. Myopia occurs when the whole eye is too long, or the cornea features too steep a curve to focus light on the retina.
• Vision issues: Both conditions can cause blurry vision for far-away objects. However, astigmatism may also result in blurry vision with nearby objects. A person with myopia may experience either high myopia or pathological myopia. These terms refer to types of myopia where a person has a higher risk of ocular complications.
• Prevalence: Refractive errors are the most common visual problem and their prevalence varies slightly throughout the world. A 2018 systematic review suggests that astigmatism is the most common refractive error. However, it may not always cause symptoms. A 2016 systematic review indicates a growing prevalence of myopia and predicts that by 2050, roughly half the global population will have myopia.
• Severity: These conditions can affect individuals differently depending on whether the condition is minor or severe. However, high myopia and pathological myopia often result in more significant vision and eye health risks.

Astigmatism occurs due to the cornea or lens having a different shape than usual. While the exact cause is currently unknown, evidence suggests that people can inherit the risk of developing an astigmatism. Additionally, it is also possible for people to develop an astigmatism due to an eye condition, eye injury, or after ocular surgery.

Myopia occurs due to the shape of the eye preventing light from correctly landing on the retina. Often, the eye is too long or the curve of the cornea is too steep. This causes the light rays to fall short of the retina. Without light focusing on the retina, people will experience blurry vision.

Additionally, risk factors for nearsightedness can include:

• inheriting myopia from a parent
• spending too much time indoors
• near work, such as having too much screen time

With cases of mild astigmatism, a person may not notice any symptoms. However, the most common symptoms a person may experience include:

• blurry vision
• eyestrain
• needing to squint to see clearly
• headache
• difficulty seeing at night

For myopia, the most common symptoms may include:

• trouble seeing distant objects
• needing to squint to see clearly
• eyestrain
• headache

Individuals with mild nearsightedness may not notice any symptoms. Those with severe nearsightedness may be at a higher risk of other eye problems, such as retinal detachment. This is when the retina pulls away from its natural position.

Typically, an eye doctor will be able to identify either condition during a comprehensive eye exam. Because refractive errors may not have any obvious signs during the initial stages, it is important to attend regular eye appointments so a doctor can check a person’s eye health.

For astigmatism, a doctor may use the following tests:

• Visual acuity eye chart: This test involves a person reading letters on an eye chart. It tests how sharp a person’s vision is at certain distances.
• Refraction: For this test, a person looks through a binocular-like device known as a phoropter and tells the doctor which lenses they can see the best through.
• Autorefraction: An autorefractor device works by shining a light into the eye and measuring how it changes as it bounces off the back of the eye.
• Keratometry: This test measures the curve of the cornea.

For myopia, an eye doctor can also use an eye chart and a phoropter to help measure how sharp a person’s vision is and whether they require a prescription to see clearly.

For those unable to read letters on an eye chart, a doctor can instead use a retinoscope. This device measures where light focuses inside the eye and can also help a doctor to measure the necessary prescription to see clearly.

In most cases, treatment for both conditions involves visual aids or surgery to correct vision.

For astigmatism, treatment options can include:

• Eyeglasses: These glasses will contain a special cylindrical lens that can compensate for the astigmatism.
• Contact lenses: Similarly, a person can wear contacts with a special shape, known as a torus or doughnut shape.
• Orthokeratology: This procedure involves fitting a series of rigid contact lenses to help reshape the eye.
• Laser and other surgeries: It is also possible to use surgical options to reshape the cornea.

Treatments to help those with myopia regain clear distance vision include:

• Eyeglasses: By wearing the correct prescription eyeglasses, it is possible to reduce refractive error and move the focus point of light back onto the retina.
• Contact lenses: Similarly, contact lenses can help correct myopia by focusing light directly onto the retina.
• Orthokeratology: By wearing these rigid contact lenses, it is possible to reshape and flatten the curvature of the cornea to help focus light on the retina.
• Laser surgery: Laser surgery treatment options can help reshape the cornea and correct vision by safely removing a thin layer of corneal tissue.
• Phakic intraocular lens implant: If a person’s cornea is too thin for laser surgery, a doctor can instead surgically implant small lenses to correct vision.
• Vision therapy: For individuals with stress-related myopia, certain eye exercises can help improve poor eye focusing and help regain clear distance vision.

Both astigmatism and myopia are common eye concerns known as refractive errors. It is also not uncommon for a person to have both myopia and astigmatism.

These conditions occur due to the eye having a different shape from usual, which changes how light focuses at the back of the eye. Both conditions can result in blurry vision and treatment options can include eyeglasses, contacts, or surgery.