Astigmatism is most likely the most misunderstood vision issue. For starters, it’s called “astigmatism,” not “stigmatism.” (You don’t have “a stigmatism”– you have astigmatism.)
Like nearsightedness and farsightedness, astigmatism is a refractive mistake, meaning it is not an eye disease or eye illness; it’s simply an issue with how the eye focuses light.
In an eye with astigmatism, light fails to pertain to a single focus on the retina to produce clear vision. Rather, numerous focus points take place, either in front of the retina or behind it (or both).
Symptoms of uncorrected astigmatism are eye strain and headaches, particularly after reading or other long term visual tasks.
Squinting likewise is a very common symptom.
Does Astigmatism Causes Blurred Vision?
Yes. Astigmatism normally causes vision to be blurred or distorted to some degree at all ranges.
What Causes Astigmatism?
Astigmatism generally is brought on by an irregularly shaped cornea. Instead of the cornea having a symmetrically round shape (like a baseball), it is shaped more like a football, with one meridian being considerably more curved than the meridian perpendicular to it.
To comprehend what meridians are, consider the front of the eye like the face of a clock. A line linking the 12 and 6 is one meridian; a line connecting the 3 and 9 is another.
The steepest and flattest meridians of an eye with astigmatism are called the principal meridians.
In some cases, astigmatism is brought on by the shape of the lens inside the eye. This is called lenticular astigmatism, to distinguish it from the more typical corneal astigmatism.
Types of Astigmatism
There are three main types of astigmatism:
- Myopic astigmatism. One or both principal meridians of the eye are nearsighted. (If both meridians are nearsighted, they are myopic in varying degree.)
- Hyperopic astigmatism. One or both primary meridians are farsighted. (If both are farsighted, they are hyperopic in differing degree.)
- Mixed astigmatism. One prinicipal meridian is nearsighted, and the other is farsighted.
Astigmatism also is categorized as routine or irregular. In routine astigmatism, the primary meridians are 90 degrees apart (perpendicular to each other). In irregular astigmatism, the principal meridians are not perpendicular. Many astigmatism is routine corneal astigmatism, which provides the front surface of the eye a football shape.
Irregular astigmatism can result from an eye injury that has actually triggered scarring on the cornea, from particular types of eye surgery or from keratoconus, a disease that causes a steady thinning of the cornea.
How Common Is Astigmatism?
Astigmatism often happens early in life, so it is necessary to set up an eye exam for your child to avoid vision issues in school from uncorrected astigmatism.
In a recent study of 2,523 American children ages 5 to 17 years, more than 28 percent had astigmatism of 1.0 diopter (D) or greater.
Also, there were substantial differences in astigmatism occurrence based on ethnicity. Asian and Hispanic children had the highest prevalences (33.6 and 36.9 percent, respectively), followed by whites (26.4 percent) and African-Americans (20.0 percent).
In another research of more than 11,000 eyeglass users in the UK (both children and adults), 47.4 percent had astigmatism of 0.75 D or higher in at least one eye, and 24.1 percent had this quantity of astigmatism in both eyes. The prevalence of myopic astigmatism (31.7 percent) was roughly double that of hyperopic astigmatism (15.7 percent).
Astigmatism is discovered throughout a regular eye exam with the very same instruments and methods used for the detection of nearsightedness and farsightedness.
Your optometrist can approximate the amount of astigmatism you have by shining a light into your eye while by hand presenting a series of lenses in between the light and your eye. This test is called retinoscopy.
Though lots of eye doctors continue to carry out retinoscopy, this handbook treatment has been replaced or supplemented in lots of eye care practices with automated instruments that provide a quicker preliminary test for astigmatism and other refractive errors.
Whether your eye examination consists of retinoscopy, an automated refraction, or both, your optometrist or ophthalmologist will perform another test called a manual refraction to improve the outcomes of these preliminary astigmatism tests.
In a manual refraction (also called a manifest refraction or subjective refraction), your optometrist places an instrument called a phoropter in front of your eyes. The phoropter consists of many lenses that can be presented in front of your eyes one at a time so you can compare them.
As you check out the phoropter at an eye chart at the end of the test space, your optometrist will show you various lenses and ask you concerns along the lines of, “Which of these 2 lenses makes the letters on the chart appearance clearer, lens A or lens B?” Your responses to these concerns assist determine your eyeglasses prescription.
How to Treat Astigmatism?
Astigmatism and followed blurred vision, like nearsightedness and farsightedness, usually can be corrected with glasses, contact lenses or refractive surgery.
In addition to the spherical lens power utilized to fix nearsightedness or farsightedness, astigmatism requires an added “cylinder” lens power to fix the difference between the powers of the 2 primary meridians of the eye.
So a glasses prescription for the correction of myopic astigmatism, for instance, might look like this: -2.50 -1.00 x 90.
- The first number (-2.50) is the sphere power (in diopters) for the correction of myopia in the flatter (less nearsighted) principal meridian of the eye.
- The 2nd number (-1.00) is the cylinder power for the additional myopia correction required for the more curved principal meridian. In this case, the overall correction needed for this meridian is -3.50 D (-2.50 + -1.00 = -3.50 D).
- The 3rd number (90) is called the axis of astigmatism. This is the place (in degrees) of the flatter principal meridian, on a 180-degree rotary scale where 90 degrees designates the vertical meridian of the eye, and 180 degrees designates the horizontal meridian.
If you wear soft toric contact lenses for astigmatism correction, your contact lens prescription will also include a sphere power, cylinder power and axis designation.
Gas permeable contact lenses are also an option. Because these lenses are stiff and optically change the cornea as the refracting surface of the eye, a cylinder power and axis may or may not be required, depending on the type and intensity of astigmatism correction needed. The exact same is true for hybrid contact lenses.
Refractive surgery such as LASIK likewise can correct most types of astigmatism. Talk about with your eye doctor which procedure is best for you.