Prescription Glasses Explanation

Prescription glasses are usually worn to help with vision correction. To obtain a prescription for eyeglasses, you must first see an optometrist or ophthalmologist, doctors who are licensed to prescribe for vision. One you are examined, you can have your glasses made according to your new prescription.

History

• Lenses as we know them today have been used for over 1,000 years. Salvino D'Armate is most often credited with the invention of eyeglasses, lenses in a frame, in the 13th century. In the 1700s, Benjamin Franklin invented bifocals, combining near and far vision into one lens.

Features

• Prescription glasses are usually convex or concave. A convex lens is thicker in the middle and thinner at the edges. People with farsightedness, also called hyperopia, wear convex lenses. A concave lens is thicker at the edges and thinner in the center. Prescription glasses for nearsightedness, or myopia, have concave lenses.

Prescription Lenses

• Lenses are prescribed by power. A spectacle prescription will designate OD for the right eye and OS for the left eye, and the power is written in .25 increments. Power can be anywhere from 0.00 to plus or minus 20.00 or higher. The higher the number, the stronger the correction. A prescription for an eye with no correction is written as PLANO.
  Glasses prescriptions may also have cyl or cylinder and axis, this is a denotation for astigmatic correction. Cylinder is also written in .25 increments, and axis can be anywhere from 001 to 180.
  There may also be ADD power to a prescription, which is the strength of the bifocal. Interpupillary distance, or PD, is sometimes written down to tell how far apart your eyes are. This information is necessary for centering a lens in front of the eye.

Function of Lenses

• Prescription glasses are usually worn for nearsightedness, farsightedness,presbyopia (bifocals) and also for other types of correction not involving distance. Lenses can help with muscle problems in the eyes, such as strabismus (crossed eyes), nystagmus (involuntary movement of the eyes), prismatic correction for helping eyes align, astigmatism (irregular curvature of the cornea), cataracts and other vision problems.

Function of Frames

• Frames are the mechanism of glasses that hold the lenses in place in front of the eyes. Spectacle frames can be made of plastic or metal and can vary in size and style. Some frames are called rimless and have only a small screw or piece of metal attached to the lenses. Rimless frames are less obvious.
  Frames come in sizes and are usually numbered in millimeters. You may see 54x20 on a frame and that means the lens size is 54 millimeters at its longest measurement, the bridge (spans across the nose) is 20 millimeters. A third, longer number on a frame, denotes temple (earpiece) length in millimeters and usually ranges from 135 to 145.

Considerations

• Opticians are the people who fill prescriptions and make glasses. Once you have a written prescription from an eye doctor, an optician can help you decide what type of lenses and frames work best for your fit, function and style.