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ASTIGMATISM

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(a·stig·ma·tism)

Astigmatism is a very common “normal variant” having to do with the shape of certain structures of the eye - the cornea, and the crystalline lens. Astigmatism causes blurred vision, often at all distances, and the struggle to see objects near and far can lead to eyestrain and headaches. It can also cause increased light sensitivity and glare perception.

There are two types of astigmatism: Corneal astigmatism, and lenticular astigmatism.

Corneal Astigmatism

The cornea is the clear dome that covers the coloured part of the eye (known as the iris). Broadly speaking, the cornea can be shaped one of two ways; it can either be completely spherical like half of a tennis ball, or not spherical (aspheric). An exaggerated example of an aspheric cornea, or corneal astigmatism, is if you picture half of a rugby ball or an American football; there is one curve in one direction, and 90 degrees to that there is a second, steeper curve. The larger the difference in between these two curves, the more astigmatism one has.

Lenticular Astigmatism

The crystalline lens sits behind the coloured part of the eye (behind the iris). The lens is oval-shaped. If the lens is a symmetrical oval, there will not be any lenticular astigmatism. If however the oval lens is not symmetrical, this will lead to lenticular astigmatism.

How Astigmatism Affects Your Vision

The cornea and the lens work to focus light coming into your eye, by refracting (bending/changing direction) the light. Light coming through a spherical cornea and symmetrical lens will lead to a sharply focused image inside the eye. Light coming through an aspheric cornea and/or asymmetrical lens will lead to a blurred image inside the eye. Combined with myopia or hyperopia, this can lead to significantly blurred vision.

Your eyes are live and dynamic organs, meaning they can change. In adolescence, the corneal astigmatism can often change, including increases or decreases in asphericity. As presbyopia kicks in, in our 40’s and 50’s and beyond, lenticular astigmatism can become an increasing factor in one’s glasses prescription.

How is Astigmatism Diagnosed?

At every comprehensive eye exam at Look & See Eyecare, a refraction is done behind the phoropter to determine any changes in nearsightedness, farsightedness, astigmatism, and reading power if necessary. A measurement called keratometry is done to measure corneal curvature. The cornea and lens are assessed for any abnormalities.

Treatment for Astigmatism

Many options to treat astigmatism exist, including glasses, contact lenses, and laser surgery.

Glasses can include your astigmatism correction. It is important to ensure that the glasses are well-aligned on your face - crooked glasses will not correct your astigmatism appropriately, and can actually worsen the blur or discomfort.

There are many contact lens options for astigmatism. Soft lenses that correct for astigmatism are called “toric” contact lenses; these are available in daily, biweekly, and monthly disposable as well as more custom lenses should that be required. Rigid (hard) gas permeable lenses are also available and can provide sharper vision. Ortho-keratology lenses are special custom lenses that are worn at night while sleeping to temporarily reshape the cornea.

Laser vision surgery is also an option, where special lasers are used to permanently reshape the cornea to decrease or eliminate astigmatism.

Contact our office to set up your appointment today!

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