When you hit 40 years of age, you start to lose the ability to focus on objects close to you -- say, within your arms reach. That's because the crystalline lens inside your eye begins to harden. So it loses the ability to flex, and increase it's focal power. This is called Presbyopia.
There's no known cure for presbyopia (which is a normal condition that comes with aging, not an eye disease.) However, there are alternative ways to regain your focusing ability at near point.
One way is with multifocal eyeglasses. Also called bifocals, progressive or trifocals. This option utilizes what's known as an 'alternating multifocal' in that you either look through the top of the lens for distance, or through the bottom of the lens for near. Essentially, there are 2 lenses (for each eye) within your frame.
When you correct presbyopia with contact lenses however, you do so with a 'simultaneous multifocal' which means your distance, intermediate and near vision are all accessed through the centre pupil zone of the lens. This is much more like the natural method of the eye when viewing at different distances.
Another factor considered in contact lens fitting, is which eye is 'dominant.' Imagine someone handed you a pen and asked you to write your name. Which hand would you use? You likely don't give it much thought and you certainly didn't consciously choose that hand. What happened is your brain chose that hand because it gives better detailed feedback and thus more information. Nothing wrong with your other hand. But your dominant hand works better.
It's the same with your eyes. You have one eye that is dominant and your brain prefers that eye when it comes to detailed distance vision. This is important for your eye practitioner to determine when fitting contact lenses.
All this means your vision with contact lenses will be different than with glasses. You'll get a more natural experience in your range depth and peripheral vision. Of course, the added benefits are many. No fogging, no glare, no frame blind spots.
There are also some potential risk factors. If you have eye disease, extreme dry eyes or if you work in a dusty environment then you may not be able to wear contact lenses. The best way to know is to get an assessment and try some diagnostic contact lenses. If you're a candidate like most people, you can experience better vision and the freedom of not wearing glasses.