Astigmatism - Types, Causes, Symptoms, Diagnosis, and Treatment

What Is Astigmatism?

Astigmatism is a condition of refractive error characterized by blurry vision. In astigmatism, the cornea or lens shows irregularities in shape, thereby preventing the proper focus of light on the retina. When there is a steep curvature change in the eye, astigmatism occurs. Depending on the changes that occur in curvature, astigmatism can either be decreased or increased.

Also, astigmatism can occur together with other vision conditions like myopia (nearsightedness) and hyperopia (farsightedness). Myopia is nearsightedness, whereas farsightedness is termed hyperopia.

It can occur in both children and adults. In children, diagnosis is a bit difficult as they will not be aware. While in adults, the presence of blurry vision helps in diagnosis. When the child has astigmatism, they can notice that they would have poor performance in studies and sporting activities due to their poor vision.

What Are the Types of Astigmatism?

Astigmatism is of two types, namely,

• Corneal:

In corneal astigmatism, irregularity occurs in the curvature of the cornea.

• Lenticular:

Irregularity in the lens curvature is the characteristic of lenticular astigmatism.

What Is the Pathology Behind the Formation of Astigmatism?

In general, there is smooth and equal curvature of the lens and cornea in all directions, which helps the light to fall sharply on the retina. When a disruption occurs on the cornea or the lens leading to rough or uneven curvature, refraction of light rays is not appropriate. This is the pathology behind the formation of astigmatism.

What Are the Causes of Astigmatism?

• In order to visualize and portray, the eye has two important curved structures, namely the lens, and cornea. When there is a distortion in these structures, astigmatism occurs. The lens is the transparent structure present on the inner side. It helps in focusing on near objects by changing their shape.

• In contrast, the cornea has a similar clear structure on the outside of the eye containing a tear film. Astigmatism occurs when there is steep curvature of the cornea or lens in one direction. It results in blurry vision, predominantly in one direction. It can be either horizontal, vertical, or diagonal.

• The exact cause of astigmatism is not clear, and it has been attributed that any eye disease, injury to the eye, or any surgery done to the eye can cause astigmatism.

• Do not fall for the misconception that watching television too closely or reading in dim light can cause astigmatism.

• In sporadic cases, keratoconus can cause astigmatism. It is a condition in which the cornea becomes thin and attains a cone shape.

What Are the Symptoms of Astigmatism?

The following signs manifest astigmatism:

• Strain in the eyes.

• Headaches.

• Blurred vision or distortion in the vision.

• Difficulty in night vision.

• Discomfort in the eyes.

• When clear vision is possible only with squinting the eyes.

How Is Astigmatism Diagnosed?

A complete eye examination with an ophthalmologist is needed for diagnosing astigmatism. When there is a distortion in the vision, reach out to the ophthalmologist at the earliest.

The following tools are engaged in diagnosing astigmatism:

1. Visual Acuity Test: An eye chart helps test the sharpness of eyesight. You will be asked to read the eye chart.

2. Phoropter: A phoropter consists of several lenses given in series to determine the lens that provides you with the best clear vision.

3. Autorefractor: Autorefractor helps in measuring the refraction. In this, light is focused onto your eye to measure the refraction. It is also helpful in determining the type of lens needed for the patient.

4. Keratometer: Keratometer is an instrument used to measure the curvature in the cornea. It determines the corneal shape and the capacity of the cornea to focus.

5. Corneal Topographer: A corneal topographer helps provide detailed information about the corneal shape. During this test, the individual is asked to focus on a specific point to enable the instrument to get small measurements about the cornea, which are then mapped. Deciding between surgery for astigmatism or cataract is done with the help of this device. The treatment plan is decided with the help of a corneal topographer.

What Does Astigmatism Prescription Mean?

The following are a few of the abbreviations used in an astigmatism prescription:

• OU - Oculus uterque or both eyes.

• OS - Oculussinister or left eye.

• OD - Oculus dexter or right eye.

The numbers in the prescription are called diopters which are the measurements obtained in the test.

• First Number - It refers to spherical correction. The minus sign represents nearsightedness, and the plus sign indicates farsightedness. Higher values mark blurrier vision.

• Second Number - Cylindrical power is the second number on your eye prescription.

• Third Number - Axis or the exact location of astigmatism on the cornea is represented by the third number.

How Are Astigmatism Treated?

Treatment of astigmatism aims to provide comfort to the eyes during vision and enhance the clarity of the vision. It involves either using corrective lenses or undergoing refractive surgery.

1. Corrective Lenses:

Distorted or uneven curvatures in the lens or cornea can be corrected using corrective lenses. Lenses can be used either in the form of eyeglasses or contact lenses. They are also helpful in correcting other conditions of refractive errors like myopia or hyperopia.

In some cases, contact lenses are engaged in a procedure called orthokeratology. In this procedure, rigid and hard contact lenses are worn at night to correct the uneven curvatures in the eye. After it gets corrected, lenses are slowly withdrawn and are less frequently used to maintain the corrected shape. However, when the treatment is fully withdrawn, recurrence is common. Also, frequent usage of contact lenses can produce eye infections.

2. Refractive Surgery:

The use of contact lenses and eyeglasses can be reduced by opting for refractive surgery. The advancements in the medical field have made refractive surgeries painless. Only an ophthalmologist can decide whether you can get refractive surgery.

The following are the different types of refractive surgeries available:

• LASIK or laser-assisted in-situ keratomileusis, is a procedure used to change the shape of the cornea permanently.
• LASEK or laser-assisted subepithelial keratectomy, is a procedure used to correct refractive index.
• PRK or photorefractive keratectomy, is a type of refractive surgery used to treat vision defects.
• Epi-LASIK, in which a special blunt blade is used instead of alcohol as in LASEK. This procedure helps to minimize the dependency on contact lenses, and eyeglasses.
• SMILE or small-incision lenticule extraction. It is a laser refractive surgery for treating myopia and myopic astigmatism.

What Are the Complications of Refractive Surgery?

• Dry eyes.

• Eye infections.

• Problems are undercorrected or overcorrected.

• Corneal scarring.

• Starburst or halo appearance around the lights.

• Vision

What Are Other Refractive Errors Present With Astigmatism?

• Astigmatism also occurs together with other refractive errors like myopia and hyperopia.
• When the cornea attains a deep curvature or when the eye is longer than normal, the focus of light occurs on the retina at a more forward point resulting in a blurry vision of the objects seen at a distance.
• Shallow curvature of the cornea or shorter eyes makes the light focus on a backward point on the retina. Thereby leading to near blurred vision.

Conclusion:

Astigmatism is an imperfection in the eye curvature that can be treated effectively to get rid of distance, blurred, or near vision. Contact lenses or refractive surgeries can correct astigmatism. Therefore, a person should consult the ophthalmologist at the earliest to treat the condition and get the best possible option for themselves.