The 4 Types of Refractive Error

It can happen to anyone: you notice that your vision is blurry at times, and you realize you may need glasses. If this happens to you, schedule an eye examination. Blurry vision most likely means you have a refractive error.

A refractive error occurs when light entering your eye is not focusing correctly on your retina. Because of this, you end up with a blurred image that's not as crisp and sharp as you're likely used to. Simply put, refractive errors are the types of visual impairments that most often lead people to get eyeglasses or contact lenses.

The important question is, what kind do you have? There are four main types of refractive errors, and the type you have will determine how it's corrected. The two most known types of refractive errors are nearsightedness (myopia) and farsightedness (hyperopia).

Learn more about the types of refractive error from the eye care professionals at Clarkson Eyecare.

Myopia

Myopia affects nearly 30% of Americans, according to the American Optometric Association. More commonly known as nearsightedness, myopia causes problems with your distance vision. That's because the eye is too long, so when the light enters it, the rays focus in front of the retina instead of directly on it. Your distance vision lessens, causing distant objects to appear blurry.

For example, if you are in a classroom, you may have trouble reading notes on the board, but you can read a notebook in front of you clearly.

Other symptoms of myopia to watch for include:

• A tendency to squint

• Headaches

• Getting easily tired when trying to view something in the distance

• Eye strain

Treatments for myopia range from spectacles and contact lenses to refractive surgery, such as laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).  Glasses and contact lenses work by refocusing the light rays entering the eye to focus on the retina. For those looking for permanent solutions, refractive surgery changes the shape of the cornea to focus light on the retina.

Hyperopia

Hyperopia, more commonly known as farsightedness, affects between 5% and 10% of Americans. Those with hyperopia have more difficulty focusing up close but can often see objects clearly at a distance. Someone with hyperopia may have difficulty reading up close but can easily read signs in the distance.

The hyperopic eye is the opposite of one that is myopic— it is too short. Because of this, light entering the eye ends up focusing behind the retina.  As a result, near objects may look blurry.

Those with hyperopia may experience the following:

• Squinting

• Eye strain

• Tiring easily when having to look at things up closely

Many children outgrow hyperopia as their eyeballs lengthen when they get older. There are also a variety of options for treating this condition, such as glasses, contact lenses and refractive surgery with LASIK or PRK. All these options help refract light directly on the retina.

Astigmatism

Those with blurred vision may have an astigmatism, a condition where the shape of the eye affects the refractive power. With this condition, either the cornea or the intraocular lens is irregularly shaped, keeping light from properly focusing on the retina.

In many cases, the cornea has a football-like shape rather than the spherical shape it is supposed to have. As a result, the eye cannot focus light rays down to a single point. This means vision may be blurry at all distances.

Astigmatism can also occur together with myopia or hyperopia.

Symptoms of astigmatism include:

• Blurred vision at all distances

• Headaches

• Eye strain

Treatment for astigmatism also includes glasses and contacts, though glasses and contacts for astigmatism differ slightly from those used for other refractive errors. Spectacles for astigmatism contain lenses with added power in certain portions of the lens. LASIK and PRK can also surgically correct astigmatism by removing tissue from the cornea so the eye can effectively focus light rays.

Presbyopia

As you age, it's normal to be affected by presbyopia. At around age 40, the eye gradually loses its ability to clearly see things up close.

The cause of presbyopia is a loss of flexibility in the lens of the eye. When you're young, the lens is very pliable and easily changes shape to clearly focus on all distances. But as you age, the lens becomes more rigid and is no longer able to change shape to focus up close.

As you begin to experience presbyopia, you may find:

• You need to hold reading material farther away.

• You need additional light to read.

• Reading material is blurred when held at a normal distance.

• You get headaches when reading.

• You experience eye strain.

Treatment options include reading glasses, bifocal or progressive (no-line) eyeglasses and contact lenses.  Glasses just for reading magnify print and make it easier to see. Meanwhile, bifocals provide two different prescriptions for distance and near in the same lens. Progressive lenses are like bifocals but offer a more gradual change between prescriptions.

Likewise, multifocal contact lenses offer a near and far focal point and an intermediate zone as well. There's also the option of monovision contacts, in which one eye is corrected for distance and the other for near vision.

In rare circumstances, it is possible to replace your eye's lens with an implant that can correct for all forms of refractive error, including presbyopia. Known as refractive lens exchange, this is a similar procedure to cataract surgery.

If things start to look a little blurry, the good news is there are numerous options that can help. It's important to get any blurring you experience checked out by an eye doctor to determine the best form of correction for you.