Firstly, I should explain that a bifocal lens has a line to delineate the distance portion of the lens (which is the top bit) and the reading or near segment.  The beauty of a bifocal lens, is that it enables the Optometrist to 

choose two separate prescriptions that can be placed in different areas of the lens.  Most commonly the two prescriptions chosen are distance for the top part and reading or near for the segment.  Which means that for people that need to walk around while wearing their safety glasses, you can see clearly in the distance and have peripheral vision (side vision) but also move your eyes down the lens to enable close vision when needed.

The majority people over the age of 40 require assistance with reading and sometimes computer distances.  Therefore having the ability to leave your glasses on and still being able to have multiple distances of clear vision is a distinct advantage for eye protection.  Regularly I hear of people saying that they only require reading safety glasses for working at the machines as an example.  I have to explain that they will not be able to walk around in their reading glasses, as the vision in the distance is blurry.  While single vision reading glasses are less expensive, my concern is that when a person gets up from their machine they take off their safety glasses to see in the distance making them vulnerable to flying debris.

Both bifocal and progressive/multifocal lenses enable multiple distances to remain clear through a set of glasses.  But only bifocals enable the wearer to have peripheral vision and a larger portion of the lens for just distance vision.  Peripheral vision is very useful when driving cars or trucks and general motility.

Disadvantages of choosing bifocal lenses include an initial adaption period where image jump can be experienced.  As you look down through the segment line into the reading area. The other disadvantage for bifocal lenses is that it can only have two distances of clear vision.  So people that like to read at say 40cm and then have a normal desk top computer set at around 70cm and then drive, will be disappointed as only two of those three things will be clear through a bifocal lens.

It is very important that when you choose your bifocal safety glasses that you have them fitted correctly.  The reason being that line which separates the distance from the reading segment needs to be in a usable position, not too high to disrupt the distance vision and not too low that you don’t have an adequate reading area.  This is why only certain frames are suitable for bifocal lenses. 

If you have any questions about ordering your bifocal safety glasses please don’t hesitate to contact us as we are happy to explain our ordering and fitting process.