Monovision and Multifocals
Monovision contact lenses
When you wear one contact lens for reading and one for distance that is called monovision. It is used to correct presbyopia or when you start to need reading as well as distance glasses or multifocals spectacles. 80% of the population can get used to wearing monovision as their brain is able to separate out the two images, one distance and one for near and can shift between them seamlessly without you noticing. It is a bit like learning to drive a manual car, in the beginning everything is harder and then it just becomes automatic and you don’t think about it.
There are some variations possible on monovision. Mini-monovision is where one eye is corrected for reading but not to the same extent as in full monovision. This will give reading vision but perhaps not enough for extended computer work. Importantly it will provide better distance vision so it is sometimes used when people cannot get used to full monovision. Modified monovision is where you have one eye for distance and one eye has a multifocal contact lens, which provides both distance and reading vision.
What are some of the problems associated with monovision?
Sometimes people cannot get used to having one eye for distance and one for reading. They find that the reduction in their distance vision is noticable and the benefit of having reading vision does not outweight this. For other people they find the loss of some depth perception (3D vision) is disturbing and they find driving can be more difficult particularly at night. For many people with monovision there will be times (such as night driving or extended computer work) where a pair of reversal glasses can be made up to help balance the two eyes together again and reduce eye strain. The night driving reversal specs are kept in the car and the computer ones at your desk, so for most of the time you are able to see without the use of glasses.
For people that have been wearing contact lens monovision for years often request the same sort of visual correct if they ever have LASIK or cataract surgery. Sometimes we do trials of monovision for people who want to have cataract surgery but still be able to read without glasses afterwards. Whilst there are some multifocal intra-ocular lenses available for cataract surgery they are not yet at the stage where everyone is suitable. It may be best to wait a few more years and the technology has stabilised.
Multifocal contact lenses
Multifocal contact lenses are available but they aren’t like multifocal spectacles in that you look down the lens to read. With contact lenses because they rotate on your eye for them to work properly the multifocality is arranged in an aspheric progression or concentric rings out from the centre of the lens towards the edge.
With multifocal contact lenses both eyes will see one image for distance and one for reading and a range in between. This is quite different to monovision where one eye sees a total distance image and the other a total reading image.
Multifocal contact lenses have been improving over the last few years and are starting to be more successful. We find monovision works in a larger percentage of people and in those it doesn’t work in we will try multifocals contact lenses.