Understanding bifocal contact lenses—how do they work?

Bifocal contact lenses are designed to help people see clearly at two distances—for instance, near and far. They combine two different prescriptions into one lens to help you enjoy clearer vision when you look from, say, a map in your hands to a road sign. Bifocal contact lenses work by ensuring that light from both near and far objects focus correctly on your retina, which is the surface at the back of your eye that helps turn light into what you see. After wearing bifocal contacts for a little while, your brain usually adapts to the different zones in the lenses, allowing you to switch from seeing far to seeing near. It’s important to note that much like how bifocal glasses have mostly been phased out in favor of progressive glasses, bifocal contact lenses have largely been replaced by more advanced types of multifocal contact lenses, which help provide clearer vision at more than two distances.

Bifocal contact lenses are actually a type of multifocal contact lenses. Multifocal simply means “more than one focal point.” Bifocal contact lenses have two focal points, while multifocals have two, three or more.

• Bifocal contact lenses:
  These lenses typically have two distinct prescription zones: one for seeing far away and one for seeing up close.
• Multifocal contact lenses:
  Multifocal lenses have two or more prescription zones. If the multifocal lenses have more than two prescription zones, they may help the wearer have clear vision when looking at things that are close, far, or at a middle distance.

Adults with presbyopia

As you get older, the lens inside your eye gets more rigid, making it harder for you to see things up close—like menus, text messages and the words on the pages of book. It’s called presbyopia, it happens to everyone and is the reason you may see so many people over 40 wearing reading glasses. Bifocal contact lenses are kind of like reading glasses built into your contact lenses. They can help people who already wear contacts rely on reading glasses less.

Children with myopia

Myopia is more than just nearsightedness, the main symptom of myopia. It’s when the eye grows too long, increasing the chance of vision-threatening eye health issues later in life. Studies indicate that specially designed multifocal contact lenses may slow the progression of myopia in children and young adults, which could help decrease the health risks of an elongated eye.

It may seem unbelievable that you could get more than one prescription in the same little contact lens, but this technology has been around for more than 70 years. There are several reasons this approach can work to help provide clear vision at more than one distance.

Two (or more) focus zones

This can be done many different ways within the contact lens (as shown below) but the most common technique currently is with what’s called “aspheric” multifocal lenses.

Some designs work with your pupils

Our pupils adjust in size depending on what you're looking at. For distance viewing, your pupils dilate a bit, while they constrict when you're focusing on something up close. Some multifocal contacts take advantage of these changes, allowing your eyes to smoothly transition between seeing near and far objects.

Your brain adapts

When you first start wearing multifocal lenses, your brain may need some time to adjust to the different zones. It might take a few days or even weeks before your vision feels comfortable. Just like getting used to a new pair of shoes, this adjustment period is normal. Some people may experience slight distortion, glare, or halos initially, but these issues typically improve as you adapt.