If you notice that you have started to move books and newspapers further away from your eyes in order to focus properly on what you are reading, chances are that you have developed presbyopia. This is a common eye condition that normally affects people in their forties whose eyes are losing elasticity, and makes it difficult to switch between focusing on near and distant objects. Thankfully, presbyopia is not dangerous at all, and most sufferers can be helped by bifocal contact lenses.
Bifocal contact lenses come in soft or rigid gas permeable materials and for daily or extended wear. Most common are the two-weekly Acuvue Bifocals. Bifocals would sometimes be referred to as multifocals, in which case the word would be used to distinguish any type of lens which comes with more than one power. Technically, however, bifocal contact lenses always have two powers for each eye while multifocals have more than two.
Simultaneous vision contact lenses require your eye to look through both powers at all times, learning to choose a power appropriate for any one situation. They come either with so called concentric ring designs or as aspherics, the former containing one prescription in the centre and another around it. RGP concentrics are normally of centre-distance design, meaning that they have the distance prescription in the centre of the lens, and soft bifocals are most commonly designed as centre-near. Aspheric bifocal contact lenses are rather like progressive eyeglasses, in that they have both powers blended across the lens.
The other type of bifocal contact lenses is called translating, or alternating vision, lenses. This means that the pupil alternates between the two powers depending on where you look. For this to work the lens needs to stay in position at all times, which is generally ensured by your lower eyelid and thanks to a much smaller diameter than that of other contact lenses.
If your optician believes that you could benefit from wearing bifocal lenses, they will find out your ‘add’ prescription and measure your pupil to decide which type of lens may be suitable. A large pupil can interfere with an aspheric lens. There are other options for presbyopes, should you find bifocal contact lenses difficult to adapt to. Monovision lenses is one alternative which involves wearing your near prescription on one eye and your distance power on the other. Thanks to modern technology, even wearers who in the past found bifocals frustrating are now able to wear them and receive almost perfect vision.