The Difference Between Toric and Multifocal Lenses
Toric contact lenses
Toric contact lenses are made from exactly the same material as spherical contact lenses. The crucial distinction between toric contact lenses and spherical contact lenses lies in the design of the lenses.
The purpose of toric contact lenses is to correct astigmatism. The term refers to an abnormal curvature of the cornea or the lens, which is not a normal spherical shape. Thus, a dot image will be projected at different points on the retina, generating a blurred image. The astigmatism can also induce myopia or hyperopia. Normally, the shape of your eye is like a football ball, but when you have astigmatism, your eyeball looks like a rugby ball.
A typical prescription for this type of lens is power, cylinder and axis.
To correct this abnormal curvature, the toric lenses need to correct the vision on a particular axis. If the lenses rotate a few degrees the vision will be blurry. They are built with a special design to allow the lenses to be stable, even if you move or jump around.
The most common stabilization system is called Prism-ballasted, involving a thickness at the bottom of the lens to stabilise it on the eye. The advantage of this system is easy handling for the wearer, and the stability itself is good. However, the difference of thickness may alter the vision. That’s why so few manufacturers have introduced new technology or improved the existing system.
Some of the designs:
- The Accelerated Stabilization DesignTM from Johnson & Johnson consists of a big lens diameter, no alteration of the optical zone and a stabilisation system on the edges. With this system, the vision is perfect and very accurate.
The Precision Balance 8|4 design from Alcon is a mix between the prism-ballasted and the ASD, with the benefit of both technologies.
Nowadays, every type of astigmatism can be corrected with contact lenses. You just need to be aware that adapting to this type of contact lens is more complex than with spherical contact lenses, which is why you may have to test different brands before finding the one that suits you.
After turning 40 years of age, a new type of ailment may occur. The lens inside your eye becomes less flexible and less transparent. Consequently, you may require an additional correction for the reading distance.
Over the past 30 years, developing multifocal lenses has been a real challenge as it requires correcting distance and reading at the same time, on a single lens surface. All manufacturers developed multifocal lenses with 2 main goals in mind, improving the optical quality with an active search for new multifocal geometries and improving comfort on the cornea.
All multifocal contact lenses nowadays use the principle of simultaneous vision. Optical performance in this type of contact lens is strongly dependent on the cortex and the pupi. Pupil diameter plays an important role as its size dictates the rays that pass through it. A Pupil on the miosis state pupil will select the central portion of the lens, whereas a bigger pupil will focus on the peripheral area. After the eye receives the image from the correct area, the brain will select itself the most accurate picture, depending on the distance you want to see. Given the size of the optical area, and the role of accommodative miosis, the near correction is generally central.
Air Optix Aqua Multifocal was one of the first silicone hydrogel multifocal contact lenses on the market. It contains a wetting agent for comfort and includes lay a surface treatment to improve comfort and the increase resistance to deposits. Its geometry is fully progressive (Precision Profile Design), with very smooth areas of transition. There is no image jump between the profiles of addition. That means that the vision is always comfortable whatever the distance. This lens was an immediate success thanks to its comfort on the eye (particularly at the end of the day) and its visual quality. Studies show that far vision suffers very little due to another correction in the lens which makes it very effective for distance vision.
Handling Air Optix Aqua is very easy. If you never handled contact lenses before, you will find it very easy to hold and to put on your eye.
These contact lenses are particularly recommended for the new presbyopic wearer.
Even if you have myopia, hyperopia or astigmatism in addition to your presbyopia you can still find a contact lens that will fit you. Overall patient satisfaction with these types of contact lenses is around 90%. Do not hesitate to ask your optician for a trial.
If I have astigmatism, should I wear toric lenses?
Contact lens manufacturers
- Alcon.com Home
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Contact lens resources
- Contact lens - Wikipedia, the free encyclopedia
- All About Vision - Complete Consumer Guide About Vision and Eye Care
A complete consumer guide to vision and eye care. Learn about eye safety, eye nutrition, LASIK, contact lenses, eye problems and treatments, and much more.