Astigmatism is one of the most misunderstood vision problems
Astigmatism is probably one of the most common vision problems but not very much understood by too many people. If you are one of them continue reading this explanation to clarify your doubts.
Like nearsightedness and farsightedness, astigmatism is a refractive error. This is like to say you do not have neither an eye disease nor a health problem.
You are simply facing a focusing problem of your eye.
In an eye with astigmatism, light does not reach a single focus point on your retina and does not produce a clear image. Instead, several focal points are produced, sometimes in front of your retina sometimes behind it, or other time on both side.
What are the symptoms of astigmatism?
Astigmatism may cause you to feel blurred or distorted vision at any distance. During night you will see the lights and cars projecting different lines of lights or a luminous shadow. Stars might appear to be longer, more than one close together or difficult to focus.
If you feel these symptoms like eyestrain and headache, this mean you have an uncorrected astigmatism. This is pretty common after reading or other tasks that require prolonged use of your vision.
Strabisms is also another very common symptom.
What is the main causes astigmatism?
Astigmatism is usually caused by irregularities in the shape of your cornea. Instead of having a symmetrical rounded shape (like a baseball), it is shaped more like a football shape, with one meridian significantly more curved than the other one.
(If you do not understand what meridians are, think of the front of your eye as a clock. A line connecting 12 o’clock to 6 o’clock would be one meridian; while a line connecting 3 o’clock to 9 o’clock would be the other meridian).
The more curved is one meridian, compared to the other meridian of your eye with astigmatism, more your sight will suffer. This is called by doctors the principal meridians.
In some cases, astigmatism is caused by the shape of the lenses inside your eye. This is called lenticular astigmatism, this is a way to differentiate it from the more common corneal astigmatism.
New theories believe this irregular shapes of the cornea are provoked by the different tension in some ocular muscles around your eyes. There is not an effective medical study capable to verify if this statement is correct or not.
There is more than one type of astigmatism?
Yes, there are three primary types of astigmatism:
- Myopic astigmatism: One or both principal meridians of your eye suffers myopia. If both meridians focus as myopic, they focus to different degrees.
- Hyperopic astigmatism: One or both principal meridians of your eye suffers hyperopia. If both focus as farsighted, they focus to a different degree.
- Mixed astigmatism: One principal meridian is myopic, and the other one is hyperopic.
Astigmatism is also classified as regular or irregular. In regular astigmatism, the principal meridians are perfectly perpendicular to each other (they form a 90 degree angle). In irregular astigmatism, they are not perpendicular. Most cases of astigmatism is suffering corneal regular, which means that the front surface of your eye is shaped like a football sphere.
Irregular astigmatism can result from an eye injury that caused damages to your cornea. This is quite common after surgery, or from keratoconus, a condition of the eye that causes thinning of the cornea.
How common is astigmatism?
Astigmatism often appears at an early age, this is the reason is important to take your child for an eye exam to prevent vision problems.
According to some study, children from 5 to 17 years old, more than 28% have an astigmatism of 1.0 diopter (D) or greater.
There are significant differences in the prevalence of astigmatism by ethnic groups. Asian and Hispanic children have the highest value (33.6% and 36.9%, respectively), followed by Caucasians (26.4%) and African Americans (20%).
Astigmatism correction options
Astigmatism, like nearsightedness and farsightedness, is normally corrected with prescription glasses, contact lenses or refractive surgery.
Some new ideas believes training and exercise of your eyes, might improve your astigmatism but there is not a proven scientific study about this systems.
In addition to the spherical lens power used to correct nearsightedness and farsightedness, cylindrical power is added to correct astigmatism to rectify the difference between the powers of the principal meridians of the eye.
Thus, the prescription of glasses for the correction of myopic astigmatism could show the following numbers to you: -2.50 -1.00 x 90.
The first number (-2.50) is the spherical power (in diopters) for myopia correction in the flatter principal meridian (the one that focuses less myopic).
The second number (-1.00) is the cylindrical power for additional myopia correction in the principal meridian of greater curvature. In this specific case, the total correction needed for this meridian is -3.50 D (-2.50 + -1.00 = -3.50 D).
The third number (90) is called the astigmatism axis. This is an indication about the location (in degrees) of your principal meridian on a 180-degree scale, where the 90th degree tells you the vertical meridian of your eye, and the 180th degree represents the horizontal meridian.
If you use toric soft contact lenses for astigmatism correction, your prescription will also include spherical power, cylindrical power and axis.
Gas permeable contact lenses are sometimes used. These lenses are rigid and optically replace the cornea as the refractive surface of your eye.
Sometimes cylindrical power and axis will sometimes not be necessary, this is related with the type and severity of astigmatism to be corrected. The same is also applied for hybrid contact lenses.
Refractive surgery such as LASIK is also used to correct the majority of astigmatism.
Anything written in this article is clearly a guide and has only some information purposes, you must discuss with your doctor which procedure would be best for you specific case scenario.