Astigmatism is a focusing problem which results in reduced clarity of vision. The word is derived from Greek “stigma” meaning “point”. “Astigma” means “no point”, because in astigmatism the light rays do not come to a point focus on the retina. Astigmatism is caused by a defect in the curvature of the eye’s cornea or lens. When the shape of the cornea or lens is not completely spherical (like a soccer ball), it has astigmatism (i.e. like a football). This imperfection of the eye is, however, generally treatable.
In Astigmatism, when light enters your eye, it gets bent more in one direction than in the other, giving blurred or unclear vision.
Types of Astigmatism
Astigmatism can be divided broadly into two types:
- Corneal Astigmatism: It is when the shape of the cornea is not spherical.
- Lenticular Astigmatism: It is when the shape of the lens is not spherical.
The pattern of astigmatism can be either:
- Regular, or
- Irregular. Irregular astigmatism cannot be corrected with glasses, and is associated with a condition known as keratoconus.
Symptoms of Astigmatism
Astigmatism can have a variety of symptoms:
- Blurry or distorted vision, usually at all distances (far and near)
- Trouble seeing at night time
Causes of Astigmatism
While there may not be a fixed cause of Astigmatism, there is a genetic or hereditary component. Many people who are near-sighted (myopia) or far-sighted (hypermetropia) can have a component of astigmatism mixed in to their focusing error.
A major risk factor for astigmatism is eye rubbing, especially in people who have allergy and constantly itchy eyes.
Eye injuries and problems with the ocular surface, such as pterygium, can also cause astigmatism of the cornea.
How can Astigmatism be Diagnosed?
Astigmatism can be diagnosed through a visit to your optometrist or ophthalmologist. They are likely to do a complete eye test to help diagnose the problem.
There are likely to be multiple eye tests, including your reading tests, to determine the clarity of your vision. The other tests could be:
- Refraction Test: A refraction test is done to determine the glasses or contact lens prescription needed to see perfectly. Your doctor will ask you to read a chart while looking through lenses of different strengths. This way, they will be able to find the lens(es) that work best for the shape of your eye. In infants and young children, retinoscopy is performed as an objective measure of refraction.
- Keratometry: Keratometry is a way for your eye doctor to measure the curvature of your cornea.
- Topography: A topography machine provides detailed information about the shape of the cornea, including whether there is any astigmatism present and whether it is regular or irregular.
How can Astigmatism be Treated?
If you have mild Astigmatism, it is likely to be cured through corrective lenses. This is the most common and easy way.
- Glasses Lenses: Theseare curved to counteract the astigmatism of the cornea or lens that is causing blurred vision, allowing you to have a clear vision. The lenses of the glasses make the light bend into your eye properly. Eyeglasses can also be used to correct the other refractive errors, such as near-sightedness or far-sightedness.
- Contact Lenses: Contact lenses are another option to correct Astigmatism. If you have mild Astigmatism, you can use toric contact lenses. These lenses are designed in such a way that they return to the same spot every time. In case you have severe or irregular Astigmatism, you may benefit from rigid gas permeable (RGP) contact lenses.
Another way of treating Astigmatism is surgery. Multiple types of surgeries can be performed for Astigmatism:
- LASIK: The shape of the cornea is changes so that it can focus light rays more precisely on the retina. The surgeon makes a thin, hinged flap in your cornea. This exposes the central layers of your cornea, and a precise specialised laser is used to sculpt the cornea into a different shape. The surgeon then returns the flap to its original position.
- Photorefractive keratectomy (PRK): In this surgery, the surgeon removes the epithelium of the cornea, without a hinge or flap. This exposes the central layers of your cornea, and a precise specialised laser is used to sculpt the cornea into a different shape. The epithelium then grows back naturally, conforming to your cornea’s new shape.
Along with the benefits, all surgeries have their own sets of risks and complications. Therefore, talk to your ophthalmologist about all the risks and complications, and to assess whether you are suitable for any of these options.
How can Astigmatism be prevented?
It is important to avoid eye-rubbing as much as possible, as it can cause and worsen astigmatism. Treatment of allergy is important to reduce itchiness, which is a trigger for eye rubbing.
If not treated, distorted or blurred vision due to Astigmatism is likely to continue for a lifetime. Treatment is usually straightforward in most patients with glasses, contact lenses, or laser vision surgery.
Dr Parth Shah is a Sydney-based ophthalmologist known for his experience in providing treatment for eye problems, including Astigmatism. He is thorough in his knowledge of modern techniques and implements them in patient care.