What Are Bifocals?

With so many different lenses on the market today, it’s no wonder that many people are asking “What are Bifocals?”

Bifocals help those that require vision correction for myopia (short-sightedness) and presbyopia (long-sightedness). The lenses allow clear vision at either distance within one pair of spectacles.

They can be thought of as ordinary prescription lenses with an additional reading segment. The reading segment is usually positioned towards the lower part of the lens.

Brief History Of Bifocal Lenses

It is thought that Benjamin Franklin invented Bifocal lenses in the late 1760s. However, evidence now suggests that others may have worn “Split Bifocals” before him. As he aged, Franklin required separate glasses for distance and near use. Growing tired of constantly changing his spectacles, he decided to do something about it. His solution was to cut the lenses from each pair in half. He then split the lens into two halves. Distance lenses at the top. Reading at the bottom. Franklin could now use one pair of glasses for clear vision at both distances. He originally named them “Double Spectacles”.

Modern technology has certainly helped to improve Bifocals. They are now more durable and stylish, as well as more widely available. But despite these technological advances, they still work largely in the same way.

D Seg Bifocals

The reading area of the D Seg Bifocal looks like a letter D positioned on its side. They may be referred to as a Flat Top Bifocal. The D Seg is the easiest Bifocal design for a wearer to adapt to. Because of this, it’s the most popular type on the market today.

The reading segment is available in various types. The most widely used lenses are D 28 and D 35. The D 28 segment is 28mm wide and the D 35 is 35mm wide.

Round Bifocals

As the name suggests, the round bifocal is round at the top. They were originally designed to help wearers reach the reading area more easily. However, this reduces the width of near vision available at the top of the segment. Because of this, round bifocals are less popular than the D Seg.

The reading segment is most commonly available in 28mm and 25mm sizes. The R 28 is 28mm wide at the centre and the R25 is 25mm wide.

Executive Bifocals

The Executive Bifocal is similar to the original Split Bifocal worn by Benjamin Franklin. The entire top portion of the lens is dedicated for distance use whilst the bottom portion is for reading. They offer a much wider reading area than other types of bifocal.

It’s not all good news, however. As mentioned earlier, the entire bottom half of the lens is dedicated to reading. This prevents the edge profile from being uniform, meaning the lenses are more difficult to glaze. This can lead to lenses looking unsightly when mounted into frames. Those with higher prescriptions and a taste for exotic styles or semi-rimless frames will want to avoid executive bifocals.

Curve Top Bifocals

The Curve Top Bifocal, or the C Bifocal, is almost identical to the D Seg. A slight curve at the top of the lens is the only difference. Once more, the near vision segments are available in different widths. The C 28 is the most popular size available.