Eye Exams

The only way to know what’s really going on with your eyes is to see an eye care professional and undergo simple eye exams that will help determine the type and severity of your vision problems.

Visiting the Eye Doctor: What to Expect

A comprehensive examination should include a review of your medical history and several tests to measure how clearly each eye sees. Preliminary tests may evaluate functions, such as depth perception, color vision, eye muscle movements, peripheral vision, and how your pupils respond to light. A test called keratometry may be done to examine the curvature of your cornea   Cornea : The clear, curved surface at the front of the eye through which light enters the eye. Along with the sclera, the cornea provides external protection for the eye.   by measuring its reflection under focused light. This is crucial in determining the proper fit for contact lenses.1

You will also need to take a visual acuity test, in which you will be asked to read letters on various reading charts, near and far, to determine the lens power needed to compensate for nearsightedness, farsightedness, or astigmatism. Using an instrument called a phoropter, your doctor places a series of lenses in front of your eyes and measures how they focus light while using a hand-held instrument called a retinoscope. In some cases, eye drops are given to temporarily keep the eyes from altering their focus during the test.1

To measure the pressure within the eye and assess risk for glaucoma,   Glaucoma: An eye disease that develops when too much pressure inside the eye damages the optic nerve due to the slow drainage of eye fluid through the eye's trabecular meshwork. Without treatment, glaucoma can cause permanent blindness within just a few years. Symptoms include halos around lights, tunnel vision and vision loss. Glaucoma is most often treated with medications designed to reduce intraocular pressure.   a test called tonometry may also be performed. Normal eye pressure ranges from 10 to 21 millimeters of mercury (mm Hg). Eyes with pressure greater than 22 mm Hg are at an increased risk for developing glaucoma.1 Click here for more on glaucoma.

What 20/20 Vision Means

The results of your visual acuity   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.   test, which determines how well you can see the shape of objects at various distances, are written as a fraction, such as 20/20, which is the "normal" distance at which healthy eyes should be able to see and is traditionally considered the baseline.

The top number means 20 feet, which is the standard distance at which testing is done. The bottom number is the smallest letter size you are able to read. A person with 20/40 visual acuity, for example, would have to be within 20 feet of a letter to see what a person without vision problems can read from 40 feet away. If you’re one of the lucky few and have superior vision, you could end up with 20/15 results, meaning what you see from 20 feet away is similar to what average healthy eyes see from 15 feet away.

Understanding Your Prescription

When doctors use the phrase 20/20, they’re measuring visual acuity, but when they write your actual prescription, they describe the degree to which your eye is out of focus using 3 different numbers. Such as:

-5.00 -1.50 x 180

  • The first number indicates the power of the lens required to correct your near- or farsightedness. If this number is negative, you are nearsighted, or short sighted. A positive number indicates that you are farsighted, or long sighted. The larger the number, the more severe your nearsightedness or farsightedness is.
  • The second number is a measure of the astigmatism in your eye since most people have some astigmatism. This number may be positive or negative, meaning it will have a plus or minus sign in front of it.
  • Astigmatism also has a direction to it, so the third number, ranging from 0 to 180 degrees, represents the axis or direction of your astigmatism.

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

To determine whether contact lenses or eyeglasses are better for you personally, read up on glasses vs contact lenses.

Next: Nearsightedness

 

References

  1. American Optometric Association. Comprehensive eye and vision examination. http://www.aoa.org/eye-exams.xml. Accessed October 16, 2010.