by Melissa J Luther

Created on: October 10, 2008   Last Updated: October 24, 2008

Eyeglasses are worn for various reasons, including eye protection or just as a fashion statement. Here we will discuss glasses used for vision correction. These come in either over-the-counter or prescription varieties. The corrective power of lenses is measured in diopters (D) and generally ranges from +6.00 to -6.00 D.

Reading Eyeglasses

Over-the-counter eye glasses are usually called reading glasses. They correct only far-sightedness (hyperopia) and come in a few strengths, usually ranging from +1.00 to +4.00 D. These are fine for people who just need a little help reading, but vision changes should always be evaluated by a qualified eye doctor, either an opthamologist (a medical doctor specializing in eyes and vision) or optometrist (an eye specialist, but not a medical doctor) to rule out any underlying problems.

Prescription Eyeglasses

Prescription glasses are custom-made, based on an individual's
vision correction needs. They can only be obtained after a visit to an eye doctor, who will evaluate eye health and visual acuity. Because they are individualized, prescription glasses can correct farsighted and nearsighted vision, as well as astigmatism.

Nearsighted (myopic) people cannot see far away objects clearly. Their own lens focuses objects in front of the retina. Light from close objects enters the eye at a different angle, so it still focuses on the retina and these objects are seen clearly. Lenses to correct myopia are measured in negative diopters (usually -1.00 to -6.00 D).

Many people who are severely myopic, or those whose eyes can't
change focus easily (presbyopia), benefit from multifocal glasses. These glasses have two (bifocal), or sometimes three (trifocal), different strengths in one lens. In traditional bifocals, the top half of the lens focuses on distant objects and the bottom half focuses on close objects. There is a distinct line between the halves and it requires conscious effort to refocus. Newer "no-line" bifocals have a smaller area at the bottom of the lens devoted to close vision, but the transition is gradual and there is no obvious transition line.

Farsighted people cannot see near objects clearly. Their eyes focus behind the retina, causing blurry vision up-close. As mentioned above, mild cases can often be corrected with non-prescription reading glasses. For more severe cases, or if accompanied by astigmatism, prescription lenses are needed.

Astigmatism is a condition in which the cornea (front of the eye) is not perfectly round. This distortion can also cause some blurring of vision. Lenses for either myopia or hyperopia can also be made to correct astigmatism.

Eyeglass Frames

Eyeglasses can be purchased from any licensed facility, as long as you have a valid prescription.

This means you are not limited to the frame choices in the eye doctor's office. This is great for people who consider their frames a fashion accessory. This fashion sense is why designer eyeglasses are so popular.

The lenses are the same no matter what frame you get, but designer frames offer a certain cachet, and some websites even give star ratings to the frames they offer. For example framesdirect.com showcases their "5-star luxury rated" glasses (Versaci, Vogue and Gucci eyeglasses to name a few) and "5-star rated styles" (Costa Del Mar, RayBan and Oakley glasses) on their homepage. Designer eyeglass frames can cost several times what an unbranded frame costs, but online sources are often a good source of discounts.

Eye exams every year or two are important to maintain eye health and determine whether or not your vision has changed since the last exam. Beyond this, though the choice of eyeglasses is as individual as you are.

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