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Understanding Your Eyes

Vision Problems

You turned to eyeglasses and contact lenses when life became blurry. When you visited your eye doctor, you probably heard about vision problems like nearsightedness, farsightedness, and astigmatism, but all that mattered was that you could see better when you left. So how do your eyes work, and what happens to your eyes when your vision becomes blurry?

How Your Eyes Work

Your eye works much like a camera. The light and images you see pass through the cornea and the lens at the front of your eye. They focus directly onto the retina, the nerve layer at the back of the eye, which then sends the image to the brain through the optic nerve.

Light rays must be bent, or refracted, by the cornea and the lens so they can focus on the retina. If you have a refractive error, the shape of your eye doesn't bend the light properly, giving you vision problems.

normal eye
With the normal eye, the images you see focus directly onto the retina, at the back of the eye.

Common Vision Problems

Your doctor can identify many of the common vision problems, including:

  • Nearsightedness - images focus in front of the retina because the eye is too long or the cornea too curved, so objects far away are blurry.
  • Farsightedness - images focus behind the retina because the eye is too short or the cornea is too flat, so objects close to you are blurry.
  • Astigmatism - images are distorted and are not uniform in all directions, so objects both near and far appear blurry.
  • Presbyopia - disorder caused by the normal aging process that typically affects reading vision.

Doctors can also measure the severity of these vision problems by evaluating the shape of your eye and its cornea. The results determine your prescription.

These problems are usually corrected with eyeglasses, contact lenses, or by laser vision correction procedures. However, good visual acuity does not necessarily mean good visual quality. Experts believe other qualitative factors contribute to common low-light vision problems, including glare and halos. You can have these vision problems and still score 20/20 on a vision exam.

Glossary Entries

nearsightedness: A common term for myopia. A condition of the eye that results in blurred distance vision. The cornea and lens focus light rays from distant objects in front of the retina. This incorrect focusing of light results in blurred images of objects at a distance.

farsightedness: A common term for hyperopia, a vision problem that most commonly results in blurred close vision. Moderate to severe hyperopia may also result in blurred distance vision. The cornea and lens focus light rays behind, rather than directly on, the retina.

astigmatism: A vision problem that results in blurred distance and/or near vision. Light rays entering the eye are bent unequally, which prevents the formation of a sharp point of focus on the retina. This creates a blurring of parts of objects you see.

cornea: The clear front surface of the eye. Refractive surgeries like PRK, LASIK, LASEK and RK reshape this surface to correct vision problems.

lens: A structure inside the eye that helps to focus light on to the back of the eye.

retina: The light sensitive nerve layer in the back of the eye that receives visual stimuli that are transmitted to the brain.

refractive errors: Vision problems caused by an imperfect optical system, most commonly myopia, hyperopia and astigmatism.

visual acuity: Another phrase for visual clarity, a measure of the eye`s ability to distinguish the shape of objects. Visual acuity is measured with a traditional eye chart, with the goal traditionally being 20/20.

halos: A visual effect, in which a circular flare or hazy ring of light may appear around a headlight or other lighted object.