A bifocal lens is created with two different areas of vision correction, which are divided by a distinct line that sits horizontally across the lens. The top portion of the lens is used for distance, while the bottom portion of the lens is used for closer vision.
The bifocal lens is available in a several different styles:
- Flat Top, it has a visible "line" and it's biggest advantage is it offers two very distinct powers. The line is obvious because the change in powers is immediate with the advantage being it gives you the widest reading area without having to look too far down the lens.
- Round Top, the line is not as obvious as in the Flat Top. It is not invisible but when worn it tends to be much less noticeable. It functions the same as the flat top, but the patient must look farther down in the lens to get the same width due to the shape of the lens.
- Blended, is a round top design where the lines have been made less visible by blending the different zones between the two powers. The advantage is cosmetic but it does create some visual distortions.
- Executive, is designed so the whole top portion of the lens is for distance and the whole bottom portion is for near vision.
- Double, is a lens design that has two bifocals built into the lens. One is inferior and the other is superior. It is used by patients that require both a distance and near power but also require to read up above their heads, such as an electrician or an airline pilot.
A trifocal lens is created with three different areas of vision correction, which are divided by two distinct lines that sit horizontally across the lens. The top portion of the lens is used for distance, the middle portion is used for intermediate vision, while the bottom portion of the lens is used for closer vision.
The trifocal is available is a few different styles:
- Flat Top, is the same design as the bifocal flat top, except has one additional section for intermediate vision such as the computer.
- Executive, is the same design as the bifocal executive, except has one additional section for intermediate vision such as the computer.
- Quadrafocal, is similar to the double bifocal above with the exception that a flat top trifocal is used on the bottom portion of the lens and a flat top bifocal is used on the top. This allows the patient when looking down to have both intermediate and near vision, straight ahead to have distance vision and when looking overhead to have reading vision.