Commentary by Dr. Jeremy Ciano
“How do bi-focal contact lenses work?” That is the million-dollar question we get asked multiple times daily. In one word, the answer is: magic! It’s actually some pretty complicated physics, but “magic” is a bit easier to comprehend unless you work for NASA or love nerdy optometric ray light diagrams, but I digress.
For the sake of simplicity, the multifocal contact lenses are designed like a bulls-eye target, with alternating zones of distance and near prescriptions. Each zone helps the patient to see clearly at different distances. Simple enough, right? We’re often asked, “But how can I ‘see’ far and up close at the same time?” Well, you can and you can’t.
Multifocal contacts work on the principle of simultaneous vision. Imagine placing a screen door in between you and another person. You can choose to focus on the screen door or the person standing on the other side. You can actually see both at the same time, but you can only focus clearly on one at a time.
The same holds true with the bifocal/multifocal contact lenses. Your brain is getting simultaneous images from each different zone but needs to choose which one it wants to see clearly at that moment in time.
Again, this sounds a lot more difficult and complicated than in actual practice, which is why “magic” covers a lot of the explanation sans physics. The reality is that most patients adapt very quickly and easily to the above mentioned complex system. Typically, it will take 48 to 72 hours for a patient to adjust to their new simultaneous vision contact lenses. And once they adapt, they will be able to enjoy clear vision at near, far and computer distances without needing reading glasses or having to suffer from the pitfalls of monovision.
