Home SEE WELL What is Astigmatism?

What is Astigmatism?

by Michael Healy

Let’s start by clearing up the semantics. The eye issue that commonly causes blurry vision is called “astigmatism.” You do not have “a stigmatism.”

Astigmatism occurs when light enters the eye, and the cornea, the front cover of the eye, cannot properly focus the light on the retina, or the back of the eye. This can occur when the cornea is misshapen. As a result, light focuses on multiple points around, in front of, and behind the retina, causing blurry vision.

Almost everyone has astigmatism, however, for many, it has no effect on their vision and they do not need any sort of treatment. For many others, astigmatism happens in tandem with near—or far-sightedness—also known as myopia and hyperopia, respectively. If gone untreated, the results of astigmatism could be a lazy eye, headaches, and fatigue.

Causes of Astigmatism

In essence, astigmatism is a refractive error.

A perfect eye with perfect vision is smooth and round like a ball, allowing light to be refracted, or bent, which, in turn, allows us to see images clearly. When there is a refractive error, the cornea is shaped more like a football and the light entering is not refracted properly.

Furthermore, the type of astigmatism taking place is determined by the meridians of the eye. If comparing the eye to a clock, one meridian would be a line connecting twelve and six o’clock across the center of the eye and another meridian would be a line connecting nine and three across the center of the eye. The most steep, flush parts of the eye are considered the primary meridians.

There are various types of astigmatism, including:

  • Myopic: occurs when light focuses solely in front of the retina.
  • Hyperopic: occurs when light focuses solely behind the retina.
  • Mixed: arises when one meridian is myopic and the other is hyperopic.
  • Corneal: occurs when the cornea is irregularly shaped.
  • Lenticular: occurs when the lens of the eye is irregularly shaped.
  • Regular: the most common type of astigmatism and occurs when the cornea takes on an oval shape and light is refracted differently in power from one meridian to another.
  • Irregular: occurs when the curve of the cornea differs along the same meridian; can also be caused by scar tissue or a thinning of the cornea.

While the exact cause of astigmatism is not entirely known, it is believed that genetics play a large role in who gets astigmatism and to what degree of severity.

Astigmatism can also occur after eye surgery or after an eye injury. Additionally, it can arise from keratoconus, a condition in which the cornea becomes increasingly more cone-shaped and thin as time progresses.

Symptoms of Astigmatism

Aside from blurry vision, which is the most common symptom of astigmatism, the following could also be potential indicators:

  • Distorted vision at every distance
  • Headaches
  • Poor night vision
  • Squinting
  • Eyestrain, discomfort or irritation[6].

Diagnosis of Astigmatism

The best way to diagnose astigmatism is through an eye exam by either an optometrist or an ophthalmologist. This should be scheduled as soon as there is a change in vision, or your vision becomes blurry. Astigmatism is diagnosed one of the following ways:

  • Retinoscopy. Retinoscopy is when an eye doctor shines a light into the eye while placing a series of lenses in front of the eye.
  • Refraction test. A refraction test is an automated version of a retinoscopy. In this case an optical refractor, or phoropter, places a series of lenses in front of the eye while a retinoscope shines light into the eye until the corrective lens needed is determined by the lens that yields the clearest vision.
  • Keratometry. Keratometry is a test imparted by a keratometer, which measures the cornea’s curvature. This is especially useful in determining correct fit for contact lenses.
  • Topography. Topography is a more sophisticated version of keratometry. A corneal topographer creates a contour map of the cornea, offering even more detail of the cornea’s curvature.
  • Visual acuity assessment test. A visual acuity assessment test is when a patient is asked to read letters off a chart placed at a specific distance across the room. The letters are in rows, varying in size with the top being the largest and the bottom being the smallest. The distance at which specific lines on the chart can be read determines visual acuity. 

Treatment of Astigmatism

Once astigmatism is diagnosed, your optometrist or ophthalmologist will use the information gleaned from one of the tests performed to also determine the power of lens correction necessary to restore clear, strain-free vision.

Astigmatism will either be corrected with prescription eyeglasses or contact lenses. Eyeglasses come in the form of single-vision corrective lenses, bifocals, or corrective lens.

The latter two are generally prescribed to patients over forty who suffer from presbyopia, a natural aging of the eye in which objects close up become difficult to see. In addition to prescription eyeglasses and contact lenses, there are more invasive corrective, yet effective, treatment options.

Soft contact lenses, which are the most common type of contact lenses, may not do the trick as far as correcting astigmatism. In some cases, rigid contact lenses are fitted to the eye via a procedure called orthokeratology, or Ortho-K.

The lenses are worn for a limited amount of time and then removed. Patients are then able to see temporarily.

For instance, lenses may be worn at night and then taken out in the morning so a patient can see throughout the day. Ortho-K only works, however, as long as the patient wears the rigid lenses, which work to repair the curvature of the cornea. Once the patient discontinues use, the astigmatism will return.

Finally, astigmatism can be corrected by surgery, such as LASIK or PRK (photorefractive keratectomy). LASIK works to correct the shape of the cornea by removing tissue from the innermost layer, whereas PRK works to correct the shape of the cornea by removing tissue from both the innermost layers, as well as the superficial layers.

These types of surgery will correct astigmatism, however, there are always potential risks associated with any surgery. Be sure to discuss these with your doctor before undergoing surgery to potentially correct your astigmatism for good.

Here’s your complete guide to prescription glasses lenses.

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