Astigmatism: Causes, Symptoms & Treatment

what is astigmatism

Astigmatism in the eye is a condition that causes light as it enters the eye to be refracted or bent unevenly. Symptoms may most commonly include blurred vision and eyestrain. Astigmatism can be managed in various ways including glasses, contact lenses, or surgical correction.

What Is Astigmatism?

Astigmatism is a common condition and is considered a refractive error of the eye similar to being farsighted or nearsighted. A person can have astigmatism in addition to being near or farsighted. With any of the refractive eye conditions, the image is not focused perfectly on the retina or back of the eye causing blurred vision or eyestrain that requires correction in the form of glasses, contact lenses, or refractive surgery.

What Happens to the Eye in Astigmatism?

A person with astigmatism of the eye will usually experience blurred vision or eyestrain that is caused when the cornea on the front of the eye or the lens inside of the eye bends or refracts light in an uneven fashion. Some will use the analogy of the eye being shaped like a football. From end to end a football curvature is flatter than the steeper curvature on the circumference of the ball, a long axis, and a short axis. When a similar curvature occurs in an eye the light from one axis of the eye is focused differently than the opposite axis causing an imperfect image on the retina which leads to blurring.

Other Refractive Errors

Refractive errors of the eye other than astigmatism also prevent the light entering the eye from being focused perfectly on the retina in the back of the eye. They include:

Types of Astigmatism

what causes astigmatism

Categorically astigmatism can be classified as regular or irregular. Regular astigmatism will have a uniform corneal shape even though the curvature may vary depending on the axis being measured. Regular astigmatism can be fully corrected with glasses, contact lenses, or refractive surgery. On the other hand, in some cases, irregular astigmatism will not be able to be fully corrected with glasses or standard soft contact lenses. Corneal conditions such as keratoconus or scarring of the cornea may be best addressed with a rigid style contact lens to obtain the best visual outcome. The rigid lens can aid in giving the front of the eye a uniform surface.

What Causes Astigmatism

Astigmatism can be a normal trait that we are born with and may be a more prevalent condition if your parents have astigmatism. The curvature of the cornea and the power of the lens in conjunction is what determines if one requires correction for astigmatism. Keratoconus is also a corneal condition that will lead to higher amounts of corneal astigmatism caused by a progressive thinning and steepening of the corneal structure. This will usually present in the first two decades of life and may require a procedure to stabilize the corneal curvature and prevent further progression (collagen cross-linking) or in worse cases require a corneal transplant. Any type of corneal scarring can also induce astigmatism.

Astigmatism Symptoms

Ocular symptoms that may be caused by astigmatism can include:

*Blurred vision at distance and near

How to Diagnose Astigmatism?

astigmatism symptoms

Astigmatism can be easily diagnosed by your eye care provider. A comprehensive evaluation of the eye and its overall health should be part of any good eye examination. Various tools can be utilized to assess and measure and manage astigmatism.

Difference Between an Optometrist and Ophthalmologist

In the United States there are two types of eye specialists. Doctors of Optometry or Optometrist prescribe glasses & contact lenses, provide routine vision examinations, and provide ever expanding medical eye care. At Discover Vision Centers refractive optometrists are an integral part of the refractive surgery care team.

Ophthalmologists are medical doctors that have done residency and fellowship training after medical school in the medical and surgical treatment of eye conditions. At Discover Vision Centers our surgeons are fellowship trained in refractive surgery.

How Common Is Astigmatism?

astigmatism treatment

All eyes of all patients have some level of astigmatism. For ten percent of the population, it is nearly imperceptible even with testing by an eye doctor. For the other ninety percent of the population if the astigmatism is corrected the patient notes an improvement in their vision. The most important risk factor for the development of astigmatism is familial.

How Is Astigmatism Measured

Astigmatism, like nearsightedness and farsightedness, is measured in a unit called a “diopter”. If you have no astigmatism the measurement is noted as “zero”. Surgical treatment of astigmatism begins when there are 0.5 diopters. Most glasses are prescribed starting at about 0.25 diopters but most doctors do not treat astigmatism with contacts until the amount is 1 diopter. Ninety-five percent of patients have 3 diopters or less of astigmatism. Glasses, contact lenses, and surgery can treat or cure several times this amount effectively with good quality of vision.

Astigmatism Treatment

Once astigmatism is diagnosed and if it is reducing vision an eye doctor is likely going to recommend treatment. Non-surgical treatments include glasses and contacts. Either soft toric (astigmatism correcting) or rigid or gas-permeable contact lenses can be prescribed. Surgical correction of astigmatism can be done on the front surface of the cornea or within the eye with a lens implant.

Surgery Procedure
Laser in situ keratomileusis (LASIK)A surgeon creates a thin flap in the cornea and then uses a laser to reshape the surface before closing the flap. This focuses the image on the retina.
Photorefractive keratectomy (PRK)A surgeon uses a laser to reshape the front curvature of the cornea which improves how light rays focus on the retina.
Small incision lenticule extraction (SMILE)A surgeon changes the shape of the cornea by using a laser to create a disc-shaped piece of tissue below the surface of the cornea.
Intraocular Lens ImplantAfter the natural lens is removed in cataract surgery or refractive lens exchange a toric lens implant can be inserted to cure astigmatism.  
Intraocular Contact Lens (ICL)In the ICL procedure a lens implant is placed behind the iris but in front of the natural lens. The ICL can be shaped to cure astigmatism.

Are Eyeglasses or Contact Lenses Better for Astigmatism?

Is one mode of correction, glasses or contacts, more effective in treating astigmatism? Astigmatism can be corrected with either contacts or glasses and mostly depends on your personal preference. However, a special type of contact lens (toric) will be necessary when correcting astigmatism.

What Are Toric Lenses?

Toric contact lenses are designed to correct astigmatism. To do this they need to align with different powers that are present when a person has astigmatism. This is accomplished by making one edge of the contact lens thicker and heavier which will utilize gravity to make this portion of the contact lens sit at the bottom of the eye. When inserting the lens one can either place this edge (notated with markings) at the bottom of the eye or it will naturally rotate to this position a couple of minutes after insertion.

Who Can Have Surgery for Astigmatism?

As long as astigmatism fits in the regular category previously discussed, surgery would be a great option to correct this. Laser vision correction (SMILE, LASIK, and PRK) or intraocular implants (LAL, Multifocal, or Toric) can all be great options when looking into surgical correction for astigmatism.

How Does Ortho-k Work?

Orthokeratology is a method in which an eye doctor prescribes a rigid contact lens that one wears at night. The contact molds or shapes the cornea. When the patient awakens they remove the contact lens. Upon removal, the vision should be clear but as the day goes on the cornea assumes its normal shape. When one stops wearing the lenses the cornea retakes its normal shape and the patient may not see clearly without glasses.

Are Their Complications Associated with Astigmatism?

astigmatism in eye

In rare situations, complications can arise from untreated astigmatism. Lazy eye or amblyopia can develop in one eye if the astigmatism is worse in one eye than the other and the person is not given correction before age 7. Also, if untreated and if the astigmatism amount is significant, eye strain, fatigue, and headaches can be experienced.

Can Astigmatism Go Away?

Astigmatism can be stable throughout a person’s life but there are situations where there can be significant increases or decreases over time.

Astigmatism Prevention

For the most part patients can not alter their level of astigmatism. The one exception is for patients that do significant eye rubbing. One can induce a medical condition called keratoconus with aggressive eye rubbing. It is recommended that patients never rub the eyeball itself.

How Do I Take Care of Astigmatism?

The first step in managing astigmatism is to have a thorough eye exam by an eye care professional. If astigmatism is diagnosed several things need to be taken into account. Is astigmatism a small, medium, or a large amount? Can glasses or soft contact lenses be used or will soft toric or rigid contact lenses be better for your lifestyle and vision needs? If you do not like those options are you a suitable candidate for surgery?

Takeaway

Astigmatism is a common condition with over ninety percent of patients having a measurable level. Astigmatism can be managed with glasses, contacts, or surgery. Contact us!


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