A typical plastic frame is made up of a frame front with metal hinges attached to each inside part of the eye wire to hold the temples. The area connecting the right eye wire to the left eye wire is called the bridge. The eye wire is what holds the prescription lens inside the frame front. Temples connect to the frame front and hold the frame on to the face by bending the end of the temple behind the ear. The eye wire, bridge and temple length are measured in millimeters.
A metal frame meets the same criteria as a plastic frame, however the bridge construction is different. The typical metal frame bridge rests on the nasal with the aid of nose pads attached to a nose pad arm that attaches to the eye wire. In some cases the metal bridge will have no nose pads and saddles over the nasal. This bridge construction is called a saddle bridge and is often called “Ben Franklin Glasses”. As in the plastic frame, the eye wire bridge and temple length are measured in millimeters.
A rimless frame has no eye wire rim holding the lenses. As in the above explanation, metal and or plastic rimless frames must have a bridge and temples. In place of the full eye wire, we have an end joint that attaches to the temple on one side and the lenses on the other side. The bridge connects the two lenses, and each lens has its own end joint. It is this construction that makes up the front of the rimless design. It is the end joint and bridge attaching to the lenses that gives it the rimless look. There are different types of end joint designs and many types of rimless frames. The more popular rimless are metal and of course are available in the various types of material explained above.
Semi rimless frames are frames that have no bottom to the eye wire. If you cut a frame front in half from top to bottom and discard the bottom portion of the eye wire, you, in effect, have a semi rimless.
Half glasses, or commonly called half eyes, are used for reading and enable the wearer to look over the top of the frame for seeing at a distance. Half eyes can be made from plastic or metal and contain the same basic components, eye wire, bridge, and temples.In most cases both plastic and metal frames are available in straight or skull temple design. A skull temple is much like a hockey stick. The bend at the end of the temple contours behind the ear to hold the frame firmly on the face. In some cases frames are available in both skull and cable temple. A cable temple is much like the letter “J”. The curl part of the temple curls around the back of the ear holding the frame firmly to the face. Athletes would prefer this type of temple design because it prevents the frame from sliding down on the face and allows a proper field of vision. The frame position on the face remains constant even when bending the face to look down. Parents of young children prefer cable or curl side temples because of a more secure fit.
FRAME MEASUREMENTThe standard by which all optical frames are measured in millimeters. The three component parts of all optical frames, eye wire, bridge, and temples are all measured using this standard. Each part uses these measurements to insure proper optical fit. The eye wire uses three factors to enable proper optical fit, horizontal, vertical, and diagonal. The bridge uses a horizontal factor and temples are measured by length.
For example, a frame size of 48 x 20 x 145 mm indicates the 48 mm is the width of the eye wire, the 20 mm is the width of the bridge and 145 mm is the length of the temple. With regard to the eye wire, the vertical, and diagonal measurements are used by the eye care professional for inserting a cut lens into the eye wire of a frame. In order for a frame to be optically correct it must fit properly* and like shoes, dresses, and suits, frames are available in different sizes. It is important when wearing an optical frame that the eye looks directly through the center of the lens.
*Savile Row is a registered trademark of Algha Group Ltd.