What Are Bifocals?
Bifocals are lenses that have a visible line in the middle of the lens, and the bottom part of the glasses is the area your eyes look through when reading. Bifocal glasses have been around for decades. Until the introduction of progressive lenses in the 1990’s, bifocals were used by everyone that wanted the convenience of near and far vision correction in the same pair of glasses. If you need vision correction for both distance and reading, then you can use two pairs of glasses, and alternate depending on what you need to see. Or, you can choose bifocal lenses, trifocal lenses, or progressive lenses (called multifocal lenses). Many people find it convenient not to be required to remove their glasses and switch to another pair in order to read something.
No Line Bifocals
No line bifocals are another name for progressive lenses, which are sometimes called progressive bifocals. Progressive lenses, which are sometimes called no-line bifocals, are actually trifocal lenses without the visible lines. Progressive lenses were developed because many people wanted the convenience of not having to change their glasses to read, but they did not like other people to see the visible line. Also, with progressive lenses there is a continuous transition from one viewing distance to the next, so there is no large jump from near to far as there is in bifocal lenses. However, many people experience problems with progressive lenses, and prefer bifocals
Multifocal lenses divide the lens so that part of the lens is for reading and part of the lens is for distance vision. The bifocal lens (two areas) and trifocal (three areas) lenses have visible lines that separate the different areas of the lens. Bifocal lenses are typically made in the Flat Top 28 style, but we also offer the upgrade lens options to the Flat Top 35 and Executive Bifocal or Franklin Bifocal Styles.
Bifocal Safety Glasses
Bifocal safety glasses were developed for work environments that require reading and distance vision. But, the lenses and frames are designed to ANSI Z87.1 specifications, for special impact resistance. Bifocal safety glasses are easy to make, just find a safety glasses frame and add safety glasses lenses to it.
Bifocal Reading Glasses
Bifocal reading glasses is another name for bifocal glasses. They have a reading section at the bottom, a visible line, and a distance vision area at the top.
Bifocal Glasses Frame
There is only one major restriction on the kind of frame that will accommodate bifocal lenses. The eyeglass frame needs to have a height of 28mm or more. Height is referred to as the “B” measurement of the frame, and is the inside measurement from the bottom to the top of the lens aperture in the frame. If you have fallen in love with a frame that has a B measurement of 27mm to 29mm, there are some new short corridor bifocal lens choices that may work for you. Contact Eyeglasses.com customer service for more information.
To fit bifocal lenses (and any multifocal lenses) properly, the eyeglass frames must first be fit and adjusted to your face. At this point, an optical professional measures the segment height of your lenses. He makes two dots on the lens, one at the bottom edge of your pupil, and the other at the intersection of the lower eyelid and your eye. The measurement in millimeters from the bottom of the lens up to each dot is the segment height.
To make any multifocal lens, we must have an accurate segment height measurement. If you send us a pair of glasses with multifocal lenses in them, we can read the lens and determine the segment height and make a perfect copy (re-lensing your glasses). But that segment height is specific to each pair of eyeglass frames and cannot be used for a different pair of frames. You can ask your local optical professional to measure the seg height for a pair of eyeglasses, and then send them to us with the markings on them. We can then make multifocal lenses. The next best alternative is to use our MFS.
Your Bifocals Prescription
Prescriptions have a certain format that is always followed. The first line of your prescription is always for the right eye, sometimes designated the OD. The second line is for the left eye, sometimes designated OS. The prescription for each eye is divided into Sphere, Cylinder, and Axis values. It is common to have no values for any one of these, in which case you might see the letters PL or plano, or to have values for all of these. Sometimes the prescription may say OU which means both eyes.
Reading a Bifocals Prescription
If your prescription is for bifocals or trifocals of progressive lenses, there may be additional information on the prescription that says, for example, “Add +2.50”. This is important information if you are ordering reading or bifocal lenses. The numbers are expressed in diopters that tell the power of the bifocal lens. A diopter is a value that is metric and universal worldwide. On a prescription for bifocal lenses, you will see information designated as add power. Your add power is simply the magnification that is added to your sphere value for distance vision, in order to create a field of view for reading. For example, if your sphere value for distance viewing is 3.00, and your add power is +2.00, then your near vision correction is 1.00. Or, if your sphere value for distance viewing is +1.00 and your add power is +2.00, then your near vision correction is +3.00.