Multifocal Lenses: Types, Function & Astigmatism
Are you over 40 years old? If so, you might consider wearing multifocal contact lenses.
You are probably much more active now than your parents were at a young age. You might cycle, jog, move a lot, and do all kinds of sports. These are just some of the activities that people over 40 enjoy regularly today.
It is therefore not surprising that many people aged 40 and over prefer to wear contact lenses instead of glasses when pursuing an active lifestyle.
Once we reach the age of mid-40s, presbyopia makes it difficult for us to focus on objects that are close by. Previously, reading glasses were the only available option for lens wearers when they wanted to read a menu or perform all those other tasks that require good near vision.
But today, fortunately, there are many options available with multifocal lenses that are certainly worth considering. Multifocal lenses offer, so to speak, the best of both worlds: you don't need glasses, and yet you get good vision both near and far.
Some multifocal lenses have a bifocal design with two different types of lenses, namely one for near vision and one for distance vision. Others have a multifocal design where the lenses work progressively, with a gradual change in the power of the lens, providing a natural transition of vision between near and far.
Multifocal lenses are available in both soft and rigid gas-permeable (RGP or GP) lens materials and are designed to be worn either daily or for extended periods, even overnight.
Some of this type of lens can be worn comfortably on a part-time basis. This is useful if you only want to wear these lenses during the weekend or on other occasions and not on a daily basis.
To make it completely comfortable, there are also soft multifocal lenses available that you only wear for one day, allowing you to simply discard the lenses in the evening. You then have no further maintenance.
In some cases, GP multifocal lenses will provide better vision than soft multifocal lenses. However, due to their somewhat tighter fit, GP multifocal lenses often require some adjustment, and it will be easier and more comfortable to wear them if you do so every day so that your eyes can get used to the contact lenses.
Hybrid multifocal lenses are a new alternative. These lenses have a GP core with a soft surrounding, which makes adjustment easier.
Multifocal designs
A commonly used contact lens design for people with myopia is a concentric bifocal pattern. With this type of contact lens, the correction for near vision is performed in a small circle in the center of the lens, surrounded by a much wider circle in which the correction for distance vision takes place.
The correction of the near distance is thus performed in the center, and that of the far distance in the outer ring.
In addition to this usual configuration, there are two other types of basic multifocal lenses:
- alternating vision
- simultaneous vision.
Alternating vision designs (also sometimes called 'translating' designs) have specific zones in the lens for near and distance vision. These designs are only available in gas-permeable lens materials.
Just like with bifocal glasses, the upper part of a multifocal GP lens with alternating vision is intended for near vision and the lower part for distance vision. These two zones are separated by an almost invisible line that your eye care professional must help you determine whether the lens fits properly.
When you look straight ahead while wearing this type of lens, you are actually looking through the part of the lens that is suitable for distance. When you look down to read, the lens remains supported by your lower eyelid. In this way, you guide your gaze through the lower part of the lens that is suitable for near vision.
With alternating multifocal lenses with segments in the shape of a half-moon or a circle, the lens maintains its own rotating position by using an area of unequal thickness in the lens that we know as a prism ballast.
In some cases, the lower part of the lens is also truncated to help with alignment and provide better wearing comfort on the lower eyelid.
Because alternating lenses are suitable for near and distance vision, this type of lens usually provides good vision when driving and reading. But they may not work as well as a simultaneous lens design for computer use and other visual tasks that are at an intermediate distance.
Simultaneous vision designs offer good results for both near and distance vision at the same time through certain parts that are in the lens just in front of the pupil. These designs are available in both soft and GP lens materials.
There are also mixed designs, such as an aspheric lens, and these can be very complex because they are intended to correct the specific vision problems you have in order to achieve the most natural vision.
This is of course work for a professional eye care specialist who will first have to determine exactly which part of your eye needs to be supported in order to be able to go for optimal vision by means of a customized type of lens in the right material.
Astigmatism
In the past, soft multifocal lenses unfortunately could not correct astigmatism. If you suffered from this eye condition, you only had the choice of rigid gas-permeable lenses for multifocal contact lenses.
Fortunately, soft multifocal lenses can now also correct astigmatism by using a toric lens design.
This type of lens achieves the correct rotating position on the eye by using unequal thickness zones in the lens to create a prime ballast effect, which is the same as that of a 'translating' GP multifocal lens.
Hybrid lenses can also correct most forms of astigmatism.
Monovision
As long as you have not found a suitable type of lens, there is no way to be sure whether you will be able to successfully adapt to wearing multifocal lenses.
If this type of lens does not feel comfortable or does not give you sufficient vision, then a monovision contact lens may be a good alternative.
Monovision lenses use your dominant eye for distance vision and the non-dominant eye for near vision. People who are right-handed are more likely to have a dominant eye on the right side, and people who are left-handed are more likely to have one on the left.
But to be able to determine this, you must have a test performed by a specialist.
Usually, single vision lenses are used for monovision. One of the advantages here is that single vision lenses cost less to replace, which can significantly reduce your annual budget for your lenses.
But in some cases, you can achieve better results by using a single vision lens on the dominant eye for distance vision and a multifocal lens on the other eye for intermediate or near vision.
In other cases, your specialist may choose to use a distance-based multifocal lens for your dominant eye and a near-based multifocal lens for the other eye. These techniques are also known as customized monovision solutions.
What if multifocal lenses don't work for you?
If, despite everything, multifocal lenses do not offer the right solution for you, your specialist can return most brands to the manufacturer in order to get a refund of your money.
If you are not a successful wearer of this type of lens, you can usually get a full or partial refund of the costs you have incurred for the material and for adjusting the lenses.
But part of the total cost picture is determined by the time and service that your specialist has spent examining your eyes, adjusting the lenses, and additional check-ups. This part of the cost will usually not be refunded.
To increase your chance of success when wearing multifocal lenses, it is important that you adjust your expectations somewhat.
This type of lens will usually not be able to provide the same clear vision that you get when wearing bifocal or progressive lenses. It is even more likely that you will still need single vision glasses or reading glasses for specific tasks such as driving in the dark or reading the fine print on, say, a package insert.
But it is reasonable to expect that multifocal lenses will offer you an overall acceptable vision for 80% of your daily activities, without the need for supplementary glasses.