Astigmatism is a visual disturbance caused by abnormalities in the curvature of the cornea or lens of the eye. This condition causes blurred or distorted vision, both at close and far distances.
Astigmatism or astigmatism can occur at the same time as nearsightedness (hyperopia) or farsightedness (myopia). Generally, abnormalities in the curvature of the eye that cause astigmatism have been present since birth. However, injury or surgery to the eye can also cause this disorder.
Based on the location of the abnormality, astigmatism is divided into two types, namely:
- Corneal astigmatism, which is astigmatism due to abnormalities in the curvature of the cornea
- Lenticular astigmatism, which is astigmatism due to abnormalities in the curvature of the eye lens
Causes and Risk Factors of Astigmatism
Astigmatism is caused by an abnormality in the curvature of the cornea or lens of the eye. It is not known what triggers the disorder, but this condition is thought to be related to heredity.
The cornea and lens are parts of the eye that function to refract and transmit light to the retina. In eyes with astigmatism, the incoming light is not refracted properly so that the resulting image becomes out of focus or skewed.
Astigmatism can happen to anyone. However, there are several other conditions that can increase the risk of astigmatism, including:
- Nearsightedness or severe farsightedness
- History of astigmatism or other eye disorders, such as: keratoconus (corneal degeneration), in families
- History of eye injury or eye surgery, such as cataract surgery
- Thinning of the corneal layer or the formation of scar tissue on the cornea
Astigmatism Symptoms
In some cases, astigmatism causes no symptoms at all. If there are symptoms, the complaints experienced by patients can vary, including:
- Distortion of vision, for example straight lines become slanted
- Blurred vision (faint) or out of focus
- Difficult to see at night
- Eyes get tired easily and feel uncomfortable
- Often squints eyes when looking at something
- Irritation to the eyes
- Headache
When to go to the doctor
Check with an ophthalmologist if you or your child experience the above complaints, especially if these complaints interfere with daily activities, such as reading or driving.
Astigmatism Diagnosis
To diagnose astigmatism and determine its size, an ophthalmologist will need to perform a thorough eye exam and cylinder eye test, including:
Visual acuity test
In a visual acuity test, the doctor will ask the patient to read a series of letters in various sizes from a distance of 6 meters.
Refraction test
This examination consists of several series of tests. The doctor will examine the form of light that enters and receives the retina to determine whether the patient has refractive errors nearsightedness, farsightedness, astigmatism, or a combination of these.
The refraction test can be done with a simple instrument called a retinoscope or with an automatic machine. If refractive errors are found, the doctor will determine the size of the refractive error.
Astigmatism is measured by a diopter scale. Healthy eyes without astigmatism have astigmatism diopters of 0. However, in most people, astigmatism diopters between 0.5–0.75 do not cause complaints.
Diopter measurements are performed by asking the patient to read a series of letters through a lensed device called a phoroptor. If the patient cannot see the letters clearly, the lens size will be changed until the letters can be read perfectly.
Keratometry
Keratometry is a procedure to measure the curvature of the cornea of the eye using an instrument called a keratometer. In addition to determining the diagnosis, this examination tool can also be used to determine the right size of contact lenses.
Corneal topography
This check works the same as keratometry, but done with more sophisticated and precise tools. Usually, this examination is done if the doctor is planning surgery to treat astigmatism.
Astigmatism Treatment
Treatment of astigmatism or cylinder eyes depends on the patient's diopter scale. Patients with mild astigmatism and no visual impairment may not require any treatment.
In patients with diopters above 1.5, doctors will generally recommend the use of glasses or contact lenses. The size of the glasses or contact lenses is determined from the results of the refraction test.
However, if the patient wants another treatment method, refractive surgery can be an option. Some of the surgical methods that can be used to treat astigmatism are:
Laser-assisted in situ keratomileusis (LASIK)
LASIK is a procedure to reshape the cornea using a laser. The goal is to correct the focus of light onto the retina.
Laser-assisted subepithelial keratectomy (LASEK)
In the LASEK procedure, the surgeon will loosen the outer layer of the cornea (epithelium) with a special alcohol and then reshape the cornea using laser. After that, the epithelium will be tightened again as before.
Photorefractive keratectomy (PRK)
PRK procedure is the same as LASEK. The difference is, in the PRK procedure, the epithelium will be removed. Epithelium will re-form naturally following the curvature of the new cornea.
Small-incision lenticule extraction (SMILES)
In astigmatism accompanied by mild nearsightedness, doctors can run SMILE to correct the shape of the cornea. This procedure is done by making a disc-shaped cut (lenticule) under the surface of the cornea by using a laser and removing it through a small incision.
Complications of Astigmatism
Astigmatism that occurs in only one eye since birth can trigger amblyopia or what is commonly known as lazy eye. This condition occurs because the brain is used to ignoring the signals sent by the eyes.
Amblyopia can be treated with blindfolds if detected before the visual pathways in the brain are fully developed.
Another complication that can occur due to astigmatism is keratoconus, which is a condition when the cornea thins and protrudes like a cone. Keratoconus can cause blurred vision. In fact, this condition can cause blindness if left unchecked.
Astigmatism Prevention
As explained above, astigmatism can cause blurred vision. In adult patients, this complaint may be easily noticed, but not in patients with infants and children. Therefore, eye examinations need to be carried out on newborns and continued periodically. The recommended schedule is:
- Age 65 years: every 2 years
- Age 65 years: once a year