All About Multi-Focal Lenses
Multi-Focal Lenses: What are they and where do they come from?
As we age, our eyes naturally begin to have difficulty focusing on objects near to us. Sometime between the ages of 40 and 50, we begin to have difficulty seeing in lower light, focusing on small objects and fine print, or noticing eyestrain. This is what is called “Presbyiopia”, and is corrected with lenses that help your eyes to focus on small or near objects.
However, some people are also already nearsighted, or “myopic”. Myopia is a condition where your eyes are unable to correctly focus on objects at a distance. This is, again, addressed by lenses that correctly bring far objects into focus.
But what to do when somebody with myopia develops presbiopia?
That question is believed to have first been solved by one of America’s Founding Fathers, Benjamin Franklin. In addition to being the leading statesmen and political theorists of the American colonies, Franklin was also one of the leading scientists in the New World. He is known for his work with lightening and electricty, but Franklin is also responsible for developing bifocal glasses to address the problem of both myopia and presbyiopia.
Ben Franklin is credited with creating the first bifocal glasses some time around the year 1780. He created by taking lenses ground to correct nearsightedness and lenses ground for farsightedness, cutting them in half, and joining the two different halves. Today lenses made in this fashion are called ‘Executive’ or ‘Franklin’ bifocals. Over time, Franklin bifocals were refined to have smaller, rounder, near-view segments to help balance the field of view.
(via Wikimedia.org )
These early bifocals, which were made by fusing two different lenses together, were fragile. However advances in manufacturing technology have led to bifocal lenses that are one single piece, which has helped to make bifocals more durable. Bifocals are great for patients with presbyopia, however they do come with some drawbacks.
The first of these is that they only correct for near and far distances, lacking a correction for middle distances. This becomes important as the user’s eyesight continues to deteriorate, and correction for middle distances becomes necessary. Additionally, bifocals’ two corrections can also cause dizziness and headaches in some users, and the smaller than ideal field of view can take getting used to.
Finally, some people feel that the obvious line inherent in bifocals are a sign of age. It isn’t uncommon for people to dislike bifocals because they feel they make the wearer look “old”.
If one of the limitations of Ben Franklin’s bifocals is that they lack a correction for middle distances, it’s only natural that eventually that limitation would be addressed. In 1827 John Isaac Hawkins patented the first trifocal lenses. Hawkins, who also coined the term “bifocal” to describe Franklin’s lenses, is also credited for inventing the upright piano, the first pointed pencil, an early mechanical pencil, and devices for filtering water.
As the name suggests, trifocal lenses have a third prescription to correct for middle distances, or distances from 18 to 24 inches in front of the user. Trifocals have typically been prescribed to presbiops who frequently read or use computers, or are 50 – or older – whose eyesight has degenerated to the point where they need the additional prescription.
Recently trifocals have fallen out of fashion in favor of progressive lenses.
The next evolution of multi-focal lenses is the advent of progressive lenses. Modern technology has lead to the creation of lenses that can incorporate a variety of prescriptions on the same lens without the need for lines. The smooth transition from one correction to another eliminates the obvious “tell” of bifocals or trifocals, which many feel lend a more youthful appearance. But appearance aside, progressive lenses have a variety of advantages over both bifocals and trifocals. The first advantage is that progressive lenses more closely mimic natural vision than either bifocals or trifocals. The smooth transition from one correction to another eliminates the “jump” in vision that comes with the abrupt change in prescriptions inherent in the lenses created by Franklin.
When patients first get progressive lenses, they may experience blurry zones in their peripheral vision, but that will typically go away in a week or two. (The dark blue areas on the lower edges of the lenses in the diagram above.)
When progressive lenses were first created, they offered relatively small fields of view. However, as technology advanced, the fields of view have increased, making progressive lenses attractive for those with an active lifestyle.
Recently, there have been several advances in progressive lens technology. The use of high-index plastic materials allow for progressive lenses that are as much as 50% thinner than bi or trifocals, making for lighter, more comfortable glasses. The greatest advancement has been the introduction of digital technology to lens production.
By moving away from traditional lens production techniques and using digital technology to design and guide manufacturing, progressive lenses have gained even more advantages over Franklin lenses. Digital technology has allowed “Free Form” lenses to be produced faster and more economically than previous multi-focal lenses. It also allows lenses to be produced with a much higher degree of precision than was previously possible. Free Form lenses can be precisely ground to take into account how the lenses are positioned in the frame (and therefore in front of the user’s face) to put the exact right prescription at any viewpoint, and make for the sharpest vision possible. The advent of digital manufacturing of Free Form lenses has allowed for crystal clear vision across a wide field of view.
Lens manufacturer Varilux has developed their “S-Fit” progressive lenses, which combine a number of technologies and advancements to create comfortable lenses that are optimized to each patient’s vision. Their lenses minimize the “swim” effect created by changing prescriptions by minimizing deformation while keeping power progression. The S series lenses are also unique in that they incorporate prescription information from both eyes to optimize binocular vision, while also emphasizing the dominant eye to enhance visual response time.
The history of multi-focal lenses is a long and surprisingly interesting one. Two of the main inventors and innovators responsible for those lenses are credited for inventions ranging from the lightening rod to the mechanical pencil.
But are multi-focal lenses – which today would likely mean progressive lenses – right for you? Well, that largely depends on the results of your eye exam. However if you need correction at multiple distances, then multi-focal glasses may be for you.