Correcting Astigmatism with Contact Lenses

May 15, 2008 by  
Filed under VISION

Astigmatism for a long time was an eye problem that could not be fully corrected with contact lenses. Mild astigmatism could be adequately improved with soft contact lenses, but there weren’t options for more severe cases. The eye problem itself results from a misshaped cornea – rather than being spherical like a ball, the cornea in people with astigmatism is oblong, shaped more like a football. Because of this shape, light rays can’t refract properly against the retina. Instead of focusing the rays on one spot, the odd shape causes light to refract in multiple locations on the retina, causing the blurred vision, regardless of distance, that is symptomatic of astigmatism.

Understanding toric contact lenses

The development of toric contact lenses opened up a whole new world of vision for people with astigmatism. Toric contact lenses don’t look any different than other soft or rigid gas permeable contact lenses, but in fact they are very different. The lenses consist of a number of different curvatures in various meridians or sections on the lens. Since astigmatism is a problem involving unbalanced meridian sections (due to the odd shape of the cornea) bringing the meridian sections back into balance is what helps produce clear vision.

Since the positioning of the various curvatures is key to improving vision, toric soft contact lenses cannot rotate – they must be held in a certain position in order to be effective. This is accomplished several ways. One way is to add weight to the bottom of the lens by building up or thickening that section. Another way is to make the top part of the lens lighter, by thinning this section.

Rigid gas permeable lenses are an option

Yet another way to correct astigmatism with contact lenses is to use rigid gas permeable lenses. These lenses are not as flimsy as soft lenses and that enables them to hold onto their shapes, even after blinking. Regular gas permeable lenses work effectively at correcting mild to moderate astigmatism, but in cases where the astigmatism is severe, it’s usually necessary to purchase gas permeable toric contact lenses. Toric lenses are custom shaped so that the inside of the lens more closely matches the shape of the astigmatism. Because of the customized fit, toric lenses remain in position and rotation isn’t an issue.

And because toric contact lenses involve customization, you’ll likely have to pay more for this type of contact lens. You might even find that your eye doctor charges more when fitting you for toric lenses because of the extra work involved in properly measuring each eye.

If you work with an eye doctor you trust, he or she will likely first try to prescribe regular contact lenses to treat your astigmatism. Again, mild and moderate astigmatism can usually be adequately corrected with standard lenses. Only when the astigmatism becomes severe is it necessary to resort to toric style contact lenses. When this happens, you’ll find that toric lenses are available as daily wear, extended wear, silicone hydrogel and disposable brands. They even come in an assortment of eye color options!

What Is Astigmatism?

March 14, 2008 by  
Filed under VISION

Astigmatism is a common eye problem in which a person’s cornea or lens has an irregular shape. These problems are known as Corneal astigmatism and Lenticular astigmatism respectively.

The cornea is a clear layer that completely covers the part of the eye that has color. Ideally, the shape of the cornea is round, like a tennis ball. The cornea’s job is to bend rays of light that enter the eye so that these light rays can be better focused on the lens enabling the retina to produce a clear image.

When the cornea has a more oval shape, like that of a football, light cannot focus properly. Instead of one focus point, as is what happens when the cornea is properly shaped, the misshapen cornea focuses light onto two areas of the retina. That is what results in blurred vision and/or the appearance of doubled vision.

Symptoms of Astigmatism

Blurred vision, ‘ghosting’ or images that are doubled are the most common symptoms of astigmatism. These types of vision problems occur at all distances. Fatigue, eye strain and frequent headaches are other symptoms that may indicate astigmatism.

Who is at risk?

The shape of the cornea can be affected by anything that causes the eyelids to exert excessive pressure on the cornea. Other risk factors for astigmatism include hereditary, poor posture and performing redundant and excessive amounts of up-close work. Those who are nearsighted or farsighted are also at higher risk of developing astigmatism. Other factors that can increase the appearance of astigmatism include head trauma or a cut, tear or scar on the cornea.

Keratoconus, a condition which over time causes the cornea to thin and take on a more cone shape can also cause astigmatism. This condition develops around puberty and affects more women than men. It’s also caused by excessive rubbing of the eyes.

Finally, diabetics are at increased risk of developing astigmatism as elevated blood-sugar levels can cause the shape of the lens to change.

Early Detection/Treatment

A routine eye exam is the easiest way to detect astigmatism. The eye doctor will do a number of tests to determine vision clarity. To determine how light rays focus on the retina the eye doctor can perform a refractive evaluation. Reading the eye chart is a good way to determine visual acuity. Checking eye muscle performance, eye coordination and eye focusing capability are also part of a routine eye exam and can all help determine the presence and degree of astigmatism. Astigmatism is measured in terms of diopters and ranges from mild to severe.

Since astigmatism is an eye condition and not an eye disease, it is highly treatable. Common treatment options include corrective eye glasses and (toric) contact lenses.

Surgical treatment options have been highly successful at correcting the shape of the cornea. Photorefractive Keratectomy or PKR uses laser beams to change the cornea’s shape. LASIK surgery involves making small incisions on the sides of cornea using laser beams. With Radical Keratectomy, laser beam incisions are made into the cornea.

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NOTE: The contents in this blog are for informational purposes only, and should not be construed as medical advice, diagnosis, treatment or a substitute for professional care. Always seek the advice of your physician or other qualified health professional before making changes to any existing treatment or program. Some of the information presented in this blog may already be out of date.