Multifocal and Bifocal Lenses
As your approach the age of 40, you notice that it is becoming increasingly difficult to read your morning newspaper. The words seem to blur on paper and you can’t make out what they say. You may encounter the same thing when it comes to reading text on your mobile device. This age related decline in the ability to read near text is called presbyopia.
Some people are near sighted. This means that they require correction if they want to view objects and words at distance. Any correction device, be it glasses or contact lenses, that address both the issue of nearsightedness and presbyopia are known as bifocal/multifocal glasses/contacts.
Multifocal and Bifocal: Difference
Bifocal means that there are two prescriptions in the same lens; the reading prescription and the power to correct nearsightedness. Multifocal contact lenses are the equivalent to progressive eye glasses where there is a spectrum of powers. Multifocal contact lenses can also have more than one power, and hence bifocal and trifocal contact lenses are categories included in them.
Both of these contacts are available in a wide range of contact types. This includes:
- Soft contact lenses: These lenses not only provide sharp vision, they are also highly comfortable to wear. They can further be available as daily disposable contact lenses, contacts that are for one time use only and need to be thrown away at night. Or those that can be used for slightly longer periods of time like a month before being replaced.
Brands: Bausch + Lomb; Alcon; CooperVision
- Rigid Gas Permeable Lenses: These lenses provide an accurate viewing experience and allow oxygen to pass through their silicone hydrogel material, helping maintain a healthy cornea.
Brands: Bausch + Lomb Ultra for Presbyopia (by Bausch + Lomb); Air Optix Aqua Multifocal (by Alcon)
- Hybrid Lenses: Those that are a fusion of the aforementioned lenses, with a rigid gas permeable center and soft contact lens material in the periphery. These offer crisp optics and great comfort.
Brands: Duette Progressive (by SynergEyes); Duette Multifocal (by SynergEyes)
Types of Multifocal Designs:
Simultaneous Vision Designs:
The lens is divided into areas dedicated to near and far vision. Depending on what the user needs to see, their eyes will make use of the designated region of the lens. They can further be divided into two designs:
- Concentric Multifocal Lenses:
In this type of design, typically the area for distance viewing is a circle in the center, surrounded by a region for near viewing. Then there are alternate concentric circles of distance and near vision. In a non-dilated and un-constricted pupil, 2 concentric circles cover the area of the pupil.
When the distance power is in the center, it is called a distance- center design. When the near power is in the center, it is called a near-center design. Soft contact lenses mostly have a near-center design, while RGP lenses usually have a distance-center design. On the other hand both designs can be present in the same pair, with the distance- center design meant for the dominant eye and the near-center design meant for the non-dominant eye.
- Aspheric Multifocal Lenses:
In this type of design, there is a steady change in the prescription, from that which corrects near sightedness to a region that deals with presbyopia. There are no clear margins that divide the near vision and far vision regions. Thus, this design is the equivalent of progressive eye glasses.
These designs are the equivalent of bifocal or trifocal eye glasses. In the bifocal designs, there top and center of the contact lens is meant for distance viewing while the bottom segment has magnifying power for reading. There is a clear line of demarcation between both regions. In trifocal designs, an added segment for intermediate vision is also added.
These contact lenses are best suited in GP lenses and not soft contact lenses. This is because soft contact lenses are mobile and move with eye movement. In contrast GP lenses have a rigid shape and they rest on a layer of tears hence they do not displace much from their place when the eye moves.
The right multifocal design for you
The design that best suits your vision needs will be selected for you by your eye doctor, after considering two factors. These are:
- The size of your pupil
- The power of your near prescription
You may need to experiment with multiple designs before you find the right fit that is both comfortable for you and also fulfills your requirements of a great visual experience. Many eye practitioners will give you free trials so that you can find your best fit. In general however:
- Aspheric Multifocal designs are best suited for those that have mild to moderate presbyopia
- Simultaneous Vision designs are great for people who have a very high near prescription and their presbyopia is quite advanced.
Alternatives to a multifocal contact lens:
Previously bifocal designs were not popular options for those that needed to correct both near and distance vision. With time however newer processes have enables multifocal lenses to be produced in a wide range of materials and designs, thus making it easier for people to find their right fit. However if they are still not right for you, there are other methods you can try:
- Monovision: You have a near prescription single vision lens in one eye and distance prescription single vision lens in the other eye.
- Modified Monovision: You have a multifocal lens in one eye and a single vision lens in the other eye.
- Progressive eyeglasses: You wear contact lenses most of the time, and use progressive eye glasses when required such as while reading. It is also great for driving especially at night as progressive eye glasses can also correct any leftover astigmatism that is not corrected by the lenses. Progressive eye glasses lack the harsh lines of demarcation that reading glasses have and are thus more fashionable to wear.