Astigmatism is one of the lesser understood vision problems, afflicting millions of Americans every year. Even the name itself is often misspoken as A-Stigmatism, when it is actually all one word, Astigmatism.
It is essentially a refractive error, that is somewhat similar to hyperopia (farsightedness) and myopia (nearsightedness.). Astigmatism isn’t an eye disease or a problem with eye health, it is a deviation that affects the eye’s ability to effectively focus light. This further impedes the ability of the eye to clearly translate this information to the brain. It tends to create multiple focus points in front of or behind the retina.
Common Symptoms Of Astigmatism
At first the early symptoms of an untreated astigmatism manifest as blurred vision or some degree of distortion that persists when trying to focus near as well as far. This causes astigmatism sufferers to squint excessively.
As time goes on chronic symptoms of uncorrected astigmatism can include eye strain and headaches, which often occur after reading or other prolonged visual tasks.
Understanding The Causes of Astigmatism
Irregularities in the shape of the cornea are the most common cause of astigmatism. A normal, healthy cornea has a symmetrical or round shape. With an astigmatism, the cornea has a more oblong shape where one meridian being curved or longer than the other. This almost gives it the shape of a football.
However, there are some cases of astigmatism that are related to an abnormal shape of the lens inside the eye. The technical term for this is a lenticular astigmatism.
It’s important to determine the difference between a lenticular astigmatism and a corneal astigmatism, as it will likely influence the treatment plan needed to correct your vision.
When Does Astigmatism Develop?
Many cases of astigmatism occur early in life. This makes your child’s eye exam critically important for diagnosing and correcting astigmatism to help prevent vision problems in their school years. Indeed, it is estimated that in the United States roughly 28 percent of children between the ages of 5 to 17 years old have some degree of astigmatism.
It’s also worth noting, that there is some ethnicity prevalence that can increase your child’s chances of developing astigmatism. Statistically Asian and Hispanic children have a higher occurrence of astigmatism than Caucasians and African-Americans.
A study performed in the United Kingdom found that more than 11,000 eyeglass wearers had astigmatism in one or both eyes. The study included both children and adults. Of these, 31.7% had myopic astigmatism, compared to 15.7% who had double hyperopic astigmatism.
Different Types Of Astigmatism
The type of astigmatism affecting you or your child can influence the treatment plan needed to properly correct your vision.
Myopic astigmatism affects one or both of the principal meridians of the eye, which results in some degree of nearsightedness.
With hyperopic astigmatism, one or both principal meridians are farsighted.
In the case of mixed astigmatism, one of the principal meridians is nearsighted, while the deviation in the other is farsighted.
Astigmatism might also be classified as irregular or regular depending on if the principal meridians are perpendicular to each other. Most astigmatisms are regular corneal astigmatism, where the front surface of the eye takes on an oval shape.
Some cases of irregular astigmatism are related to a previous eye that caused scarring of the cornea. In some rare cases, it might be related to eye surgery to treat an eye disease like keratoconus.
Diagnosing An Astigmatism
A routine eye exam is an essential first step in diagnosing and determining an effective treatment plan for astigmatism. You should tell your eye doctor if you or your child has been experiencing astigmatism symptoms, which could include eye strain, headaches, and excessive squinting. This simple outpatient appointment employs the same techniques and precious instruments used for detecting nearsightedness or farsightedness.
When a deviation is found, your eye doctor will be able to evaluate the degree of astigmatism by shining a light into the affected eye or eyes. A series of manually adjusted lenses will then be introduced. This retinoscopy will determine the type and severity of the issues with your cornea, which will be factored into the correction or treatment plan.
Automated refraction is also another diagnostic technique for detecting and defining the type as well as the degree of astigmatism. As the name implies it uses automated instruments to test for refractive errors in the eye.
Treatment Options For Correcting An Astigmatism
Astigmatism that causes farsightedness or nearsightedness can often be corrected with contact lenses or prescription eyeglasses. With some cases, refractive eye surgery may be needed.
Astigmatism may require a cylinder lens power in addition to the spherical lens power used to correct the nearsightedness or farsightedness. In a case like this, an eyeglasses prescription to correct myopic astigmatism might be -2.50 -1.00 x 90.
With this, the first number -2.50 indicates the sphere power measured in diopters for the correction of the nearsighted principal meridian of the affected eye.
The -1.00 is the cylinder power necessary to correct additional myopia for the more curved principal meridian. In a case such as this the total correction required for the meridian is -3.50 diopters expressed as -2.50 + -1.00 = -3.50 D.
The third number, 90 indicates the axis of astigmatism, which is essentially the location of the flatter principal meridian in degrees.
With soft toric contact lenses, the prescription for the contact lens would likewise include a sphere power, and cylinder power, as well as the axis designation. In some of these cases, gas permeable lenses might also be an effective option. This type of lens is designed to be rigid and it will optically replace the cornea as the primary refracting surface of the eye.
There’s no doubt about it. Astigmatism can impact not only you or your child’s vision. It can have a major impact on quality of life. Fortunately, some basic diagnostics can easily diagnose the problem as an easy first step toward correction.