Understanding Astigmatism: Causes & Treatments
Astigmatism isn’t a disease. It’s one of a group of eye conditions called refractive error disorders. Other examples include myopia or being near-sighted and hyperopia, which is also called farsightedness.
Vision is impaired in all three of these because light entering the eye isn’t refracted or bent correctly. In order to see clearly and sharply at all distances, light coming into the eye must focus on the right spot on the retina.
The retina is at the back of the eye. It sends light signals to the brain for interpretation and conversion into the images we see. If you think of all the light sources around you, all that light must enter the eye, be refracted correctly, and land precisely on the retina.
When this doesn’t happen, refractive errors occur. Myopia is when the light focuses in front of the retina. Farsighted people have this light focusing beyond or behind the retina.
Astigmatism is a bit different. The refraction problem here is located somewhere along the curves of your cornea or lens. Where this refraction error occurs, it causes astigmatism, which generally produces distorted vision.
It’s possible to have astigmatism along with myopia or hyperopia. You can also have neither of those and just astigmatism. If so, and the degree is high enough, you may require corrective lenses even though you don’t also have myopia or hyperopia.
Many people have some degree of astigmatism. If mild, it may not require correction. It doesn’t necessarily occur in both eyes or to the same degree in both eyes.
These may include headaches, eye strain, squinting, double vision in one or both eyes, faulty night vision, and blurred, fuzzy vision at all distances.
Diagnosis of Astigmatism
As part of your vision exam, your eye care professional will scan your eyeball to give a three-dimensional picture. Astigmatic sections are identified along lines called meridians.
Think of the face of a clock. An eye meridian may run from top to bottom, such as the line running from the 12 to the 6 on the clock’s face. Another meridian may run from the 9 to the 3 and follow the line between those.
Eye doctors then calculate the high and low spots generating astigmatism and causing light to bend incorrectly as it enters the eye.
Measurements of eye correction are called diopters. Diopters in the negative, such as -5.00, would indicate myopia. Those in the positive range, such as +2.00, indicate hyperopia.
When shown on a prescription for corrective lenses, astigmatism will be expressed as the CYL or cylinder. You will also see an axis number next to this. This indicates the direction of astigmatism.
If you see nothing in the CYL column of your eyeglass prescription, then you either don’t have astigmatism, or it’s too mild to need correction.
Your eye doctor may assess your astigmatism with a test called a retinoscopy. This involves shining a light into your eyes as you look through a series of possible corrective lenses.
This test helps your eye doctor compare differences between the meridians and decide how to correct your particular case of astigmatism best.
Kids and Astigmatism
When a newborn looks like they’re struggling to see you clearly, it’s because they are. Astigmatism is common at birth, but it generally resolves within the first year of life. By ages five to nine, astigmatism in children is uncommon.
However, not all kids will outgrow their astigmatism. When this occurs, it can impact school performance and even social development.
This is only one reason why children need regular eye exams the same as adults do. Your eye care professional can detect astigmatism and other refractive problems so they can be corrected early.
Types of Astigmatism
There are three basic types: myopic, hyperopic, and mixed. This is in reference to the principle meridians, which are the steepest and flattest.
In the myopic type, the principal meridians are nearsighted. In the hyperopic type, the main meridians are farsighted.
Mixed astigmatism has both near-sighted and farsighted principle meridians, but astigmatism is the primary refractive error.
Other Astigmatism Terms
The condition can be corneal, lenticular, regular, or irregular. The corneal term refers to defects in the cornea, the lenticular, in the lens. Astigmatism can be caused by both or either.
Regular astigmatism means the principal meridians are 90 degrees apart, while these meridians are not perpendicular in the irregular form.
Keratoconus, thinning of the cornea, may sometimes cause irregular astigmatism, as can injuries, scarring, and some types of eye surgery.
Treatment of Astigmatism
Although certain types of refractive eye surgery like LASIK and others can correct astigmatism in some cases (but not all), treatment consists primarily of corrective eyeglasses and contact lenses.
In most cases, regular astigmatism should be correctable to 20/20 vision. Irregular astigmatism may not be correctable to 20/20. Not all degrees and circumstances of astigmatism can be fixed in all cases.
Types of Contact Lenses for Astigmatism
There are several types of contact lenses designed for astigmatism:
Toric: These unique soft lenses utilize complex technology to align the eye’s meridians, giving precise vision correction in suitable candidates. As you may expect, the technology of these lenses brings a higher price.
Gas Permeable: These are rigid lenses correcting the refraction errors of the cornea. They may do a better correction job than soft toric lenses, but there may be initial issues with comfort.
However, gas permeable offers the best vision correction and comfort levels as the wearer adjusts to them over time.
Hybrid: These are rigid in the center but soft at the edges. The firm center gives better visual clarity; the soft edges aid in comfort. Many eye care professionals regard hybrids as the best of both worlds.
Fitting all three types requires expertise, time, and patience to get the best possible fit and visual clarity.
Surgery for Astigmatism
LASIK refractive eye surgery uses precision lasers to reshape the cornea. It can correct a moderate degree of astigmatism in the process. Surgery to remove cataracts can also reshape the cornea and potentially correct astigmatism.
The cataract surgeon can also remove the cataract and insert a toric intraocular lens or IOL simultaneously, eliminating astigmatism. An IOL may not be for everyone. IOL surgery is permanent.
Only your eye care professional can diagnose and recommend treatment for you in your individual case. If you want to explore more information on eye conditions and diseases click here.
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