These are lenses that help us see at all distances while using 1 pair of lenses with different strengths to allows us to focus at distance, intermediate or near .
Common types of Multifocals: Bifocals, trifocals and progressive lenses.
There are segmented lenses that allow for distance and near vision. Bifocal lenses are recommended for those who need immediate attention to near vison without the hassle of having to switch between distance and near glasses. The segmented line sits at the lower edge of the lower lid so this will not interfere with distance vision. The segmented line gives you a clear view of the area designated for near focus. This does not include intermediate vision and therefore means you would either have to get closer to an object at intermediate distance and use the near segment or you would have to get farther away from an intermediate object to be able to use the distance area.
These lenses are double segmented lenses that allow for distance, intermediate and near vision. This works much like the bifocal described above with an added benefit of an additional segmented line to incorporate an intermediate view that is the same width as the near segment. The intermediate segment can vary in size This makes it easier to see the computer without causing neck strain and without requiring you to move closer to the computer to see it.
These lenses are nonsegmented, no line, correction that allows for vision at distance, intermediate and near. It has a variable corridor of vision that increases as you look down along the center of the lenses for detailed viewing as you get closer to an object.
Progressive lenses can be made to adjust the width of the corridor to allow for a wider range of viewing as shown below. Usually this does not affect distance viewing, the following pictures just emphasize the hallway of vision created by adjusting the near corridor width.
How to use Multifocal glasses Keeping your posture is very important to appropriate use of lenses to avoid discomfort or dizzy sensation from inappropriate use of the lenses. Looking straight will allow you to see far away and the lower half is only meant for viewing computer and near vision and should not be used to look down at the floor. To perform computer work with multifocal lenses, the ideal position for a computer is about 10 degrees lower than your straight ahead viewing to allow you to easily access the intermediate zone.