Types of Astigmatism And How They Can Be Corrected
Astigmatism is a type of refractive error characterized by an irregularly shaped or non-spherical cornea, the outer front surface of the eye. Although this condition may sound concerning, it’s relatively common, affecting approximately 1 in 3 individuals around the world.
Additionally, astigmatism doesn’t affect the health of the eye, but rather how the eye focuses light onto the retina.
A perfectly spherical cornea refracts all the light entering the eye with the same focusing power, so there is one focal point within the eye. An astigmatic eye, on the other hand, has two different refracting powers of light, so there are two focal points within the eye that affects visual clarity.
Most people with astigmatism also have other refractive errors, like myopia (nearsightedness) or hyperopia (farsightedness).
The hallmark symptoms of astigmatism are:
- Blurred vision (both near and far distances)
- Difficulty with night vision
- Irritated eyes
- Frequent eye strain
There are 3 types of astigmatism and several ways to correct this refractive problem.
Types of Astigmatism
The 3 main classifications of astigmatism are based on the principal meridian of each eye. Think of the eye’s meridian as a plane or axis of the eye — for example, the horizontal meridian and vertical meridian.
When the horizontal axis is steeper than the vertical, it creates a stronger focusing power in the horizontal meridian. The difference in the focusing powers results in two different focal points on the retina and the blurry vision associated with astigmatism.
1. Myopic Astigmatism
When one or both of the eye’s principal meridians is myopic (focuses light in front of the retina), the result is myopic astigmatism. There are 2 subdivisions of myopic astigmatism:
- Simple myopic astigmatism: when incoming light creates 2 focal points — one in front of the retina and one in the correct position — directly on the retina.
- Compound myopic astigmatism: when the 2 focal points are both in front of the retina, and in separate locations.
Examples of this type of astigmatism as they appear on the optometrist’s prescription are plano /-2.00 x 180 or -2.25 / -1.00 x 90.
2. Hyperopic Astigmatism
Hyperopic astigmatism occurs when both or one principal meridian is farsighted (focuses light behind the retina).
This type of astigmatism is also divided into 2 types:
- Simple hyperopic astigmatism: when one focal point lands correctly and directly on the retina, and another virtual focal point sits beyond the retina.
- Compound hyperopic astigmatism: when both focal points are 2 separate virtual locations behind the retina.
Examples of this type of astigmatism as they appear on the optometrist’s prescription are +2.00 /-2.00 x 180 or +3.25 / -1.00 x 90.
3. Mixed Astigmatism
Mixed astigmatism is when one principal meridian is farsighted (beyond the retina) and the other is nearsighted (in front of the retina).
Regular vs. Irregular
Another way to classify astigmatism is regular vs. irregular. Regular astigmatism is when the principal meridians are either horizontal or vertical meridians, and irregular astigmatism occurs when the principal meridians are not at the horizontal or vertical angles, such as 135 or 45 degrees.
Examples of this type of astigmatism as they appear on the optometrist’s prescription are: +2.00 /-2.00 x 135 or +3.25 / -1.00 x 45
Ways to Correct Astigmatism
Whether you have myopic, hyperopic or mixed astigmatism, your vision will be blurred. The degree of blurred vision will vary from patient to patient. Your optometrist will recommend the most suitable corrective method for your eyes.
For people with mild to moderate astigmatism, prescription lenses in the form of glasses or standard contact lenses do a fine job of correcting the refractive error.
Another option for correcting astigmatism is through refractive surgery; however, this choice is less popular due to the possible complications of surgery.
For patients with high levels of astigmatism, standard contact lenses usually aren’t an option due to the highly irregularly-shaped cornea. Instead, scleral contact lenses are a safe, comfortable and effective way to correct vision for hard-to-fit eyes.
Why are Scleral Lenses Optimal For Astigmatic Eyes?
Scleral lenses have a larger diameter than standard soft lenses. The large lens vaults over the cornea and sits on the sclera (the white of the eye) with a nourishing reservoir of fluid in between the lens and the cornea.
The customized scleral lens acts as an artificial cornea, creating a new corneal shape that refracts light correctly for clear and comfortable vision all day long.
Scleral lenses are made of high-quality material and maintain a rigid shape, so the lens remains stable, no matter the degree of astigmatism.
What’s more, many optometrists prescribe sclerals to their patients with corneal abnormalities as a therapeutic tool in post-surgery patients.
Scleral contact lenses provide crisper and more stable vision than standard soft lenses, in addition to offering a continuously nourishing and breathable environment for the cornea.
How We Can Help
Our knowledgeable and experienced eye care team is trained to fit all types of patients with scleral lenses. Our goal is to provide each patient with crisp and comfortable vision, no matter their level of astigmatism or corneal abnormality.
Our optometry clinic has the latest diagnostic technology to provide you with the most efficient and accurate eye exam.
To schedule a consultation with Dr. Heather Shear O.D., contact Northwestern Eye Associates Scleral Lens and Keratoconus Center today.Our practice serves patients from Mt. Dennis, Toronto, York, and Rockcliffe Smythe, ON and surrounding communities.