Eyeglass Fitting Terms

Sometimes doctors, including your eye care practitioner, toss around terms that seem more like a foreign language than actual words. Eyeglass fitting tips are no different -- words like "pantoscopic tilt" or "lens thickness" sound more like rides at an amusement park or photography lessons than information about your glasses. Understanding some basic eyeglass dispensing terms helps you select the best-fitting pair of eyeglasses.

Frame Size

• The numbers on your frame seem like a code to crack a safe. Frame sizes are measured in millimeters and are written out as the lens size, bridge size and temple length. An example of a frame size is 48 x 22 x 145. This means the lens size is 48 mm, the bridge is 22 mm and the temple, the part that goes over your ear, is 145 mm long. Frame manufacturers determine the size for each style and usually make several sizes in each style.

Lens Thickness

• "Coke-bottle" lenses is a common term people use to describe thick eyeglass lenses, but most opticians refrain from using it. The more nearsighted or farsighted you are, the thicker your lenses. Nearsighted, or myopic lenses are thicker at the edges and farsighted, or hyperopic lenses are thicker in the center. Lens material affects thickness. Plastic is the thickest type of material for lenses; glass, polycarbonate and high-index lenses are thinner.

Bifocal Height

• Bifocal height is an optical dispensing term that is used to describe most styles of lenses that contain more than one correction, or prescription, for distance and up-close. A standard bifocal is measured so that the top of the bifocal rests along the edge of the lower lid. A trifocal or progressive, a multi-focal lens without lines, is measured higher, just under the pupil. Opticians frequently refer to these as "bifocal" height as well.

Pupillary Distance

• The distance between your pupils is important for eyeglass fitting because it tells the optical lab where to place the optical center of your lenses. This helps you see best through your glasses. "Pupillary Distance," or "PD" is also used for bifocal placement in the lenses.

Pantoscopic Tilt

• Your face has curves, and your frame has to match the curves to sit properly and help you see as well as possible. Pantoscopic tilt, also called "panto" or "tilt," refers to the vertical plane of your frame. Most frames need to be adjusted so they sit with the bottom of the lenses closer to your cheeks and the top of the lenses out and away from your forehead. The tilt is usually very minor and follows the natural curve of your face. Frame fit is individualized, and pantoscopic tilt has to be matched to your unique face shape.