Nearsightedness, farsightedness, astigmatism, and presbyopia are all types of refractive errors that affect the ability of the eye to focus light on the retina. If you have one or more of these conditions, you are probably used to wearing glasses or contact lenses in order to see clearly. If your doctor diagnoses you with cataracts and recommends that you seek treatment, he may also recommend a treatment option that can correct both cataracts and refractive errors.

What Are Nearsightedness, Farsightedness, Astigmatism, and Presbyopia?

Nearsightedness (or blurred distance vision) is the common term for myopia and the most common type of refractive error. Its most common cause is an eye that is too long, or a cornea that is too steep. This extra length causes light from distant objects to focus at a point----before reaching the retina and then dispersing--providing the brain with an image that is out of focus.

Farsightedness (or blurred near vision) is the common term for hyperopia. Hyperopia is caused by an eye that is too short or a cornea that is too flat. When the eye is too short, the reduced length does not give the cornea and lens sufficient space to bring the light rays to a focal point upon the retina. When the cornea is too flat, it does not bend the light rays from near objects sufficiently to bring them into focus.

Astigmatism affects the curvature of the cornea. Corneas with pronounced astigmatism are less round and more football shaped. Astigmatism causes the eye to be unable to focus clearly at any distance.

Presbyopia is a condition that affects everyone, usually between the ages of 40 and 50. As the natural lens of the eye ages, it often hardens and is less able to accommodate. This loss of flexibility in the lens, which can occur independently of cataracts, is often accompanied by a loss of near vision. This loss of flexibility or accommodation of your lens is commonly called presbyopia.

Can Refractive Errors Cause Cataracts?

In general, none of these common refractive errors can cause cataracts. There does, however, appear to be an association between extreme nearsightedness or high myopia and cataracts, meaning that people with extreme nearsightedness tend to be more prone to developing cataracts. The medical reason for association is unknown.

Can Cataracts Cause Refractive Errors?

Because a refractive error is simply the inability of the eye to focus light on the retina, anything that affects the eye's focusing ability, such as a cataract, causes a refractive error. This is why in the beginning stages of cataracts, a change in your eyeglass or contact lens prescription may be all you need to see clearly.

A nuclear cataract causes you to be more nearsighted. When a nuclear cataract develops, the nucleus of your eye's lens becomes more curved, thus, increasing the refractive index of the lens.

If you are farsighted and develop a nuclear cataract, you may notice a temporary improvement in your vision as the new nearsightedness compensates for your farsightedness. This condition does not mean your cataract is "cured." The cataract will continue to progress and this improvement will not last.

Cataracts cannot cause presbyopia, though because both are age-related conditions, many people suffer from both conditions at once.

Things to Consider in Cataract Treatment

Nearsightedness, farsightedness, astigmatism, and presbyopia are not impediments to cataract treatment. Because nearsightedness, farsightedness, and most types of astigmatism are caused by irregularities of the cornea and not the lens, cataract surgery, which replaces the lens, can usually proceed without concern. And because presbyopia and lenticular astigmatism are caused by irregularities of the lens, replacing the lens during cataract surgery can actually help with these conditions.

If you have had LASIK surgery or other kinds of laser vision correction to correct any kind of refractive error caused by an irregularity in your cornea, you are still able to have cataract surgery. But since a procedure has already been performed on your eyes, your physician will conduct additional tests to determine your best possible vision. Your doctor may also ask you to obtain your pre- and post-operative LASIK data for reference, if possible.