- Risk Factors
What is astigmatism?
The word astigmatism comes from the Greek "a" meaning "without" and "stigma" meaning "spot."
To see clearly, the eye must be able to focus light into a single plane at the surface of the retina. In astigmatism, a point (or spot) of light is focused at two different planes, causing blurred vision.
An optical system (or eye) without astigmatism is called "spherical" and has only one plane of focus for all rays of light. An optical system with astigmatism is one in which rays that propagate in two perpendicular planes have different foci. For example, if an optical system with astigmatism is used to form an image of a plus sign, the vertical and horizontal lines will never be in focus at the same time, since they are in sharp focus at two distinctly different distances from the plus sign.
- In an eye without astigmatism, the surface of the cornea is shaped like a sphere the way a ping-pong ball is, where all the curves are the same. This is called a spherical surface.
- In an eye with astigmatism, the surface of the cornea is shaped more like the bottom of a spoon, where there are two different surface curves located 90 degrees apart. This is called an astigmatic or toric surface.
What are the different types of astigmatism?
There are various classification systems for astigmatism, based on the anatomical source of astigmatism, the regularity/irregularity of astigmatism, or the direction of astigmatism.
- Most astigmatism in the human eye has its source within the cornea, although there are irregularities of the lens that can lead to astigmatism, known as lenticular astigmatism.
- Most corneal astigmatism is regular, signifying that the cornea is most curved (steepest) 90 degrees away from the surface of the cornea that is the least curved (flattest) and that the transition from most curved to the least curved surface occurs regularly.
- Regular astigmatism can be corrected with:
- Toric soft lenses
- Rigid lenses
- Refractive surgery
- Irregular astigmatism is defined as the focus resulting from any corneal surface that is neither spherical nor regularly astigmatic. It cannot be corrected with glasses or soft contact lenses.
Historical classification of astigmatism differentiates “with the rule” astigmatism from "against the rule" astigmatism:
- In "with the rule" astigmatism, the steepest curvature (the most curved part of the corneal surface) lies in or close to the vertical meridian, similar to the surface of a spoon lying on its side.
- In “against the rule” astigmatism, the steepest (most curved) part of the cornea is in or close to the horizontal meridian, similar to the surface of a football standing upright.
What is the main cause of astigmatism?
Most astigmatism does not have a recognized cause but merely is an anatomical imperfection in the shape of the cornea, where the front curvature of the cornea is toric, rather than spherical.
A small amount of astigmatism is considered normal and does not represent a disease of the eye. This type of astigmatism is extremely common and frequently is present at birth or has its onset during childhood or young adulthood. Astigmatism can increase in amount during the growing years.
- There is some hereditary basis to most cases of astigmatism, and most people with astigmatism have it in both eyes in a symmetrical fashion.
- Astigmatism is often associated with myopia (nearsightedness) or hyperopia (farsightedness).
- In regular astigmatism, the meridians in which the two different curves lie are located 90 degrees apart.
- Most astigmatism is regular. In irregular astigmatism, the two meridians may be located at something other than 90 degrees apart or there are more than two meridians.
- A scar in the cornea, resulting from an injury or infection, may also cause astigmatism.
- Astigmatism can be caused by ocular surgery, including cataract surgery and corneal transplantation.
- Certain diseases of the eye, such as keratoconus or pellucid degeneration, will cause irregular astigmatism.
What are the risk factors for astigmatism?
Individuals with a family history of high degrees of astigmatism or keratoconus are at risk for astigmatism.
Additionally, people who use power tools without safety glasses are subject to the type of injuries that may cause acquired astigmatism.
What are signs and symptoms of astigmatism?
In an eye with astigmatism, vision is blurred due to the inability of the optical elements of the eye to focus a point object into a sharply focused point image on the retina. Astigmatism makes it difficult to see fine details, both close-up and at a distance.
Small amounts of astigmatism may not be noticed at all. Sometimes uncorrected astigmatism can lead to the following:
Astigmatism is detected by an ophthalmologist by either checking for the need for glasses (refraction) or measuring the curvature of the front of the cornea by using a keratometer or corneal topography machine. These tests are noninvasive and painless.
IMAGESSee a picture of eye diseases and conditions See Images
How is astigmatism diagnosed?
The diagnosis of astigmatism is easily and painlessly made during a complete eye examination.
This would include a refraction (measuring the eyes for the need for glasses), an examination with a slit lamp, and measurements of the curvature of the corneas using various forms of light and computer algorithms.
Can astigmatism be corrected?
Many patients with mild astigmatism have no symptoms from this and require no treatment.
- If there is regular astigmatism and it causes blurred vision, astigmatism can be compensated for satisfactorily with eyeglasses or contact lenses.
- If myopia or hyperopia is also present, glasses or contact lenses can also correct that condition.
- If the astigmatism is irregular or of a high degree, glasses or a soft contact lens may not fully correct astigmatism and a hard (rigid) contact lens may be necessary to allow the eye to see normally.
- Neither glasses nor contact lenses permanently correct the curvature abnormality.
- Modern refractive surgery, which reshapes the surface of the eye with a laser, can also be used to reduce or eliminate astigmatism.
- Wavefront-guided LASIK or photorefractive keratectomy (PRK) can also reduce irregular astigmatism.
Various considerations involving ocular health, refractive status, and lifestyle frequently determine whether one option may be better than another.
What is the outlook for astigmatism?
About 30% of all people have astigmatism. In the vast majority of those cases, the condition does not change much after the age of 25. The presence of astigmatism as a child or young adult does not signify that an eye disease will later occur.
Progressive astigmatism can occur with the following:
- Corneal trauma
- Repeated infections of the cornea
- Degenerative diseases such as keratoconus
Can astigmatism be prevented?
The common types of astigmatism cannot be prevented.
The incidence of astigmatism due to trauma to the cornea can be decreased by attention to eye safety.
- CDC Warns of Potentially Fatal Bacterial Illness on U.S. Gulf Coast
- Helping Others as Volunteers Helps Kids 'Flourish': Study
- FDA Approves Pfizer's RSV Shot for Older Adults
- What to Do When Tough-to-Treat Lymphoma Strikes During Pregnancy
- Rate of Pregnant U.S. Women Who Have Diabetes Keeps Rising
- More Health News »
Health Solutions From Our Sponsors
Top Astigmatism Overview Related Articles
Can PRK Surgery Correct Astigmatism?PRK surgery may be done to correct one of these refractive errors: nearsightedness (myopia), difficulty seeing distant objects, farsightedness (hyperopia), and astigmatism - curvature of the cornea or lens is uneven, leading to distorted or blurred vision.
Corneal DiseaseThe cornea is the clear outer layer of the eye. If it is damaged by disease, infection, or injury, vision problems may occur. Corneal problems can be detected by having an eye exam. Corneal problems can be prevented by protecting the eyes from injury and avoiding contact with people who have eye infections.
Double Vision (Diplopia)Double vision (diplopia) is a symptom that my indicate Graves' disease, myasthenia gravis, stroke, multiple sclerosis, Guillain-Barre syndrome, diabetes, cataracts, aneurysm, brain tumor, or migraine. Symptoms and signs include eye pain, droopy eyelids, nausea, headache, and a cross-eyed appearance. Treatment of double vision depends upon the underlying cause.
Common Eye ProblemsEye diseases can cause damage and blindness if not treated soon enough. Learn the warning signs and symptoms of common eye conditions such as glaucoma, cataracts, pink eye, macular degeneration and more.
Eye PictureThe eye has a number of components which include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous. See a picture of the Eye and learn more about the health topic.
Eye StrainEye strain is a symptom caused by looking at something for a long time. Symptoms and signs include redness, light sensitivity, headaches, and blurred vision. Symptoms may be treated by closing the eyes and taking a break from the visual task.
Eyewear SlideshowLearn about your eye care needs and fashion wishes -- with eye glasses, frames and eyewear for computer use, reading, driving, sports and more.
Fatigue and Exhaustion
Fatigue can be described in various ways. Sometimes fatigue is described as feeling a lack of energy and motivation (both mental and physical). The causes of fatigue are generally related to a variety of conditions or diseases, for example, anemia, mono, medications, sleep problems, cancer, anxiety, heart disease, and drug abuse.Treatment of fatigue is generally directed toward the condition or disease that is causing the fatigue.
HeadacheHeadaches can be divided into two categories: primary headaches and secondary headaches. Migraine headaches, tension headaches, and cluster headaches are considered primary headaches. Secondary headaches are caused by disease. Headache symptoms vary with the headache type. Over-the-counter pain relievers provide short-term relief for most headaches.
Laser Eye SurgeryHow does LASIK work? Get information on this popular laser eye surgery, the procedure, success rates, and possible vision side effects from LASIK eye surgery.
LASIK Eye SurgeryLASIK (laser in situ keratomileusis) eye surgery is a procedure in which a laser is used beneath the corneal flap to reshape the cornea. This process is used to treat refractive errors, improve vision, and eliminate or reduce the need for contact lenses or glasses. LASIK eye surgery comes in three main types: conventional LASIK, wavefront-optimized LASIK, and wavefront-guided LASIK.
LTK Laser Eye SurgeryLTK is a type of laser eye surgery that is used to treat farsightedness and astigmatism. The procedure involves using a laser to shrink and reshape the cornea. Potential side effects include sensitivity to light and the sensation of having a foreign object in the eye.
Photorefractive KeratectomyPRK is a type of laser eye surgery that is used to correct nearsightedness, farsightedness, and astigmatism. The procedure involves using a laser to reshape the cornea. Potential side effects include seeing a mirror glare, seeing mild halos, and loss of best vision achieved with glasses.
Questions To Ask Before SurgerySurgery is the branch of medicine that employs operations in the treatment of disease or injury. Prior to surgery you might consider asking your surgeon questions about the operation (procedure).