Astigmatism is the result of an inability of the cornea to properly focus an image onto the retina. The result is a blurred image.
Usually it is caused by an irregularly shaped cornea (called corneal astigmatism). But sometimes it is the result of an irregularly shaped lens, which is located behind the cornea; this is called lenticular astigmatism. This will also cause the person to have blurry vision. What the blur looks like will depend upon the amount and the direction of the astigmatism. A person with nearsightedness (myopia) or farsightedness (hyperopia) may see a dot as a blurred circle. A person with astigmatism may see the same dot as a blurred oval or frankfurter-shaped blur.
What causes lenticular astigmatism?
Lenticular astigmatism is very common and is caused by problems in the lens of the eye. Minor variations in the curvature of the lens can produce minor degrees of astigmatism. In these patients, the cornea is usually normal in shape. Infants, as a group, have the least amount of astigmatism. Astigmatism may increase during childhood, as the eye is developing.
It is said that the tendency to develop astigmatism (not astigmatism in itself) is inherited and that therefore some people are more prone to develop astigmatism than others.
Diabetes can play a role in the development of astigmatism. High blood sugar levels can cause shape changes in the lens of the eye. This process usually occurs slowly and, often, is only noticed when the diabetic has started treatment to control their blood sugar. The return to a more normal blood sugar allows the lens to return to normal and this change is sometimes noticed by the patient as farsightedness. Because of this, diabetics should wait until their blood sugar is under control for at least one month to allow vision to stabilize before being measured for eyeglasses.
What are the symptoms
- Distortion or blurring of images at all distances.
- Headache and fatigue.
- Squinting and eye discomfort or irritation.
Parents can notice that a child may have astigmatism when the child can see some part of a pattern or picture more clearly than others. For example, lines going across may seem clearer than lines going up and down.
People with severe astigmatism will usually have blurred or distorted vision, while those with mild astigmatism may experience headaches, eye strain, fatigue or blurred vision at certain distances.
The symptoms described above may not necessarily mean that you have astigmatism. However, if you experience one or more of these symptoms, contact your eye doctor for a complete examination.
Astigmatism may increase slowly. Regular eye care can help to insure that proper vision is maintained.
How is lenticular astigmatism diagnosed
Patients seek treatment because of blurred vision. A variety of tests can be used to detect astigmatism during the eye exam. The patient may be asked to describe the astigmatic dial, a series of lines that radiate outward from a centre. People with astigmatism will see some of the lines more clearly than others. One diagnostic instrument used is the keratometer. This measures the curvature of the central cornea. It measures the amount and direction of the curvature. A
can measure a larger area of the cornea. It can measure the central area and mid-periphery of the cornea. A keratoscope projects a series of concentric light rings onto the cornea. Misshapen areas of the cornea are revealed by noting areas of the light pattern that do not appear concentric on the cornea. Because these instruments are measuring the cornea, it is also important to have a refraction in case the lens is also contributing to the astigmatism. The refraction measures the optics or visual status of the eye and the result is the eyeglass prescription. The refraction is when the patient is looking at an eye chart and the doctor is putting different lenses in front of the patient's eyes and asks which one looks better.
How can lenticular astigmatism be treated
If the degree of astigmatism is slight and no other problems of refraction, such as nearsightedness or farsightedness, are present, corrective lenses may not be needed. If the degree of astigmatism is great enough to cause eyestrain, headache, or distortion of vision, prescription lenses will be needed for clear and comfortable vision.
The corrective lenses needed when astigmatism is present are called Toric lenses and have an additional power element called a cylinder. They have greater light-bending power in one axis than in others. Your eyecare professional will perform precise tests during your eye examination to determine the ideal lens prescription. Refractive surgery may be able to correct some forms of astigmatism.
The Toric lenses can be in eyeglasses or contact lenses. The unit of measure describing the power of the lens system or lens is called the diopter (D). The lenses are shaped to counteract the shape of the sections of cornea that are causing the difficulty. Because the correction is in one direction, it is written in terms of the axis the correction is in. On a prescription, for example, it may say -1.00 X 180°. Cylinders correct astigmatism, minus spheres correct myopia, and plus spheres correct hyperopia.
There is some debate as to whether people with very small amounts of astigmatism should be treated. Generally, if visual acuity is good and the patient experiences no overt symptoms, treatment is not necessary. When treating larger amounts of astigmatism, or astigmatism for the first time, the doctor may not totally correct the astigmatism. The cylindrical correction in the eyeglasses may make the floor appear to tilt, thus making it difficult for the patient at first. Generally, the doctor will place lenses in a trial frame to allow the patient to try the prescription at the exam. It may take a week or so to get used to the glasses, however, if the patient is having a problem they should contact their doctor, who might want to recheck the prescription.
Contact lenses that are used to correct astigmatism are called toric lenses. When a person blinks, the contact lens rotates. In toric lenses, it is important for the lens to return to the same position each time. Lenses have thin zones, or cut-off areas (truncated), or have other ways to rotate and return to the correct position. Soft toric lenses are available in a variety of prescriptions, materials, and even in tints. Patients should ask their doctors about the possibility of toric lenses.
In 1997, the Food and Drug Administration (FDA) approved laser treatment of astigmatism. Patients considering this should make sure the surgeon has a lot of experience in the procedure and discuss the possible side effects or risks with the doctor. In the case of keratoconus, a corneal transplant is performed if the astigmatism can not be corrected with hard contact lenses.
The major risks of surgery (aside from the surgical risks) are over and under correction of the astigmatism. There is no cure for over correction. Under correction can be solved by repeating the operation. However we suggest using an alternative method like Eyerobics to improve your vision naturally. This can save you the risks and costs of surgery.
How can Eyerobics help
The Eyerobics program is a program of eye exercises based on the Bates Method. This is a well known method developed by Dr William Bates in the 20's.
The eye exercises are designed to address most eye disorders including astigmatism by improving the function of your eye muscles and at the same time relaxing them. The focus on improving your eye muscles enables your eyes to adjust to the abnormally shaped cornea. Especially when astigmatism is caused by an abnormal curvature of the lens Eyerobics has been very effective in restoring clear sight.
"After four eye operations, 25 years in glasses and contact lenses, and still having problems I discovered Eyerobics.
In 2 weeks I started getting results and such clear vision that I removed my contact lenses and have never used them since. I made a visit to my eye specialist in Melbourne. I wanted an unbiased opinion so I didn't mention what I had been doing.
After he examined me, he told me my eyes were great and I wouldn't need glasses or contacts again. I couldn't be happier with the results, so simple and yet noticing each day the major improvements."
Tracey McIvor - Euroa, Victoria.