Eye glasses and contact lenses

Lenses for correcting or improving vision

There are two types of lenses prescribed for correcting or improving vision. These include:

• Eyeglasses - Eyeglasses, the most common form of eyewear used to correct or improve many types of vision problems, are a frame that holds two pieces of glass or plastic, which have been ground into lenses to correct refractive errors. Refractive errors can include nearsightedness or myopia (difficulty seeing far away), farsightedness or hyperopia (difficulty seeing close up), and astigmatism (blurring due to an irregularly shaped cornea). Eyeglasses perform this function by adding or subtracting focusing power to the eye's cornea and lens. 
• Contact lenses - Contact lenses are worn directly on the cornea of the eye. Like eyeglasses, contact lenses help to correct refractive errors and perform this function by adding or subtracting focusing power to the eye's cornea and lens.

How to read an eyeglass prescription

The lens power of eyeglasses is measured in diopters. This measurement reflects the amount of power necessary to focus images directly on to the retina. When looking at an eyeglass prescription, you will see the following abbreviations:

O.D. - Oculus dextrus simply refers to the right eye (sometimes the abbreviation RE is used).

O.S. - Oculus sinister refers to the left eye (sometimes the abbreviation LE is used). 

In addition, the eyeglass prescription may also contain the following measurements:

• Sphere - This number measurement reflects the extent of the nearsightedness or farsightedness.
• Cylinder - This number measurement refers to the amount of astigmatism (an irregularly shaped cornea which causes blurring) in the eye.
• Axis - This number measurement describes the direction of the astigmatism in degrees.

Bifocal is additional power in the lens and has an additional measurement listed on the prescription as "add," to indicate the strength of the lens.

What are the different types of eyeglass lenses?

The type of lenses used in eyeglasses depends on the type of vision problem, and may include:

• Concave lenses - are thinnest in the center. Used to correct nearsightedness (myopia), the numerical prescription in diopters is always marked with a minus (-) symbol.
• Convex lenses - are thickest in the center, like a magnifying glass. Used to correct farsightedness (hyperopia), the numerical prescription in diopters is always marked with a plus (+) symbol.
• Cylindrical lenses - curve more in one direction than in the other and are often used to correct astigmatism.

Eyeglasses for children

If old enough, let your child play an active role in choosing his/her own glasses. The following are features to consider when buying eyeglasses for children:

• Shatterproof and impact resistant lenses - especially for children who participate in sport activities.
• Scratch-resistant coating on the lenses.
• Spring-loaded frames that are less likely to be bent or warped.
• Silicone nose pads that prevent glasses from slipping.
• Cable temples (ear pieces that wrap around the ear) - recommended in children under 4 years. Straps may also be recommended to hold the glasses in place.

Facts about contact lenses

Almost 25 million Americans wear contact lenses, half of whom wear daily wear soft lenses. Currently, there are five types of contact lenses in use, including the following:

• The original "hard" lens
• The rigid, gas-permeable lens
• Other rigid lenses
• The soft, water-absorbing lens
• Other flexible, non-water absorbing lenses

Reading a contact lens prescription

The prescription for contact lenses includes more information than what is available on the prescription for eyeglasses. Special measurements are taken of the curvature of the eye. In addition, your child's physician will determine if the eyes are too dry for contact lenses, and if there are any corneal problems that may prevent a person from wearing contact lenses. Trial lenses are usually tested on the eyes for a period of time to ensure proper fit.

The contact lens prescription usually includes the following information:

• Contact lens power (measured in diopters, like eyeglasses)
• Contact lens base curve
• Diameter of the lens

Unlike eyeglass prescriptions, eye care specialists are not required by federal law to give you a copy of your child's contact lens specifications.