Monovision

What is monovision?

Monovision is a vision correction technique that helps with focusing on up-close objects when you have conditions like presbyopia or cataracts. This technique changes your eyesight so one of your eyes is best at focusing on objects up close and the other is best for focusing on objects far away. Another name for monovision is “blended vision.”

You need close-up focus for everyday tasks that involve reading and writing. Monovision is useful because it restores that ability and still lets you keep the ability to focus on things far away.

There are also multiple ways that you can get monovision. Some of these give you permanent monovision, but others are temporary and you can switch between monovision and your unaltered eyesight at will.

Why is monovision used?

Your ability to focus your sight on objects up close relies on specific muscles in the ciliary body of your eyes. Those muscles automatically adjust the shape of the lens, which focuses light onto your retinas. The adjustments help your eye focus on whatever you’re looking at. That process is known as the accommodation reflex.

But for many people, the accommodation reflex weakens as they get older. The most widely accepted explanation is that the lens of your eye loses flexibility as you age. Eventually, the ciliary muscles can’t pull hard enough to change the shape enough for you to focus on close-up objects.

An age-related loss of up-close focusing ability is a condition with its own name, “presbyopia” (from Ancient Greek words that together mean “old eyes”). It’s why older adults sometimes hold objects farther from their faces to read them (unless they’re using reading glasses or other types of corrective eyewear).

People who undergo cataract surgery in just one eye may also benefit from a monovision artificial lens. An eye surgeon can place the artificial lens during the procedure to remove the cataract-clouded lens.

How common is monovision?

Monovision is a very common treatment. About 10 million people in the U.S. have some form of it. The condition it treats, presbyopia, is extremely common.

What are the forms of monovision?

There are a few different ways that you can have monovision corrections to your sight. Some of them involve corrective lenses you can wear for just part of the day. Others involve surgery or laser procedures that permanently change your sight. The different ways you can have monovision include:

• Contact lenses.
• Laser vision correction surgeries, like laser in-situ keratomileusis (LASIK) or photorefractive keratectomy (PRK).
• Intraocular lens placement or replacement surgery.

What are the advantages of monovision?

Monovision is a popular treatment for presbyopia because it has several advantages:

• It restores your ability to focus on objects that are up close without giving you nearsightedness (myopia) in both eyes.
• You can do a trial run to see how it works before committing to procedures that cause permanent monovision.
• If you want monovision but can’t or don’t want to undergo surgery for any reason, you can get monovision from contact lenses.

What are the disadvantages of monovision?

Monovision is a helpful treatment option for many people, but there are a few reasons why it might not be the best option for you, including:

• Trouble adapting to the change.
• Loss of depth and contrast perception.
• The Pulfrich effect.

Trouble adapting to the change

Some people have trouble adjusting (or can’t adjust at all) to using one eye for up-close focus and the other for far-away focus. That’s one reason why experts almost always recommend a trial period before you undergo any surgery to give you permanent monovision.

Loss of depth and contrast perception

Your eyes are supposed to work together to give you a three-dimensional (3D) view of the world in front of you. But monovision means you can’t focus both eyes on objects that are up close or far away. Without the ability to focus both eyes that way, you can’t have depth perception and 3D vision.

Using both eyes to focus on a single object also lets your brain compare the two images and process what it sees more effectively, especially the differences between light and shadow (that difference is called contrast). Without both eyes to focus on an object, your brain can’t process contrast differences as well.

The Pulfrich effect

If your brain doesn’t process input from both eyes at the same time, it has trouble judging distance, movement direction and whether or not objects are 3D. This is the Pulfrich (pronounced “PULF-rick”) effect, named for its discoverer, German scientist Carl Pulfrich. That effect is why 3D glasses in movie theaters work. The glasses make your brain process input from one eye a tiny fraction of a second slower, and your brain turns that into the illusion of seeing things in 3D.

Since Carl Pulfrich discovered this effect in 1922, experts have found that certain medical conditions can affect the timing of how your brain processes signals from your eyes. An example is multiple sclerosis, which can disrupt how fast signals travel through your optic nerves to your brain.

But in 2019, researchers figured out that your brain also doesn’t process input from a clearly focused eye and a blurry eye at the same time, with the same distance misjudgment issues seen with the Pulfrich effect. If it happens while you’re driving, that can create potentially dangerous situations (and the effect can cause bigger misjudgments at higher speeds or in low-light situations).

Because of that, you may want to talk to your eye care specialist further about monovision and how it might affect your everyday life. An eye specialist can also take your concerns into account when recommending treatment options.

How can I take care of myself if I have monovision?

If you have monovision, your eye care specialist can monitor your eye health and eyesight with regular eye exams. You should get these exams every one to two years, or more frequently if your eye care specialist recommends it. (Some medical conditions, like Type 2 diabetes, can affect your eye health and make more frequent eye exams necessary.)

If you notice you’re having issues with seeing in certain situations because of your monovision, your eye care specialist can also help with that. They may be able to provide corrective lenses like glasses that you wear only in specific situations like driving, leaving you free to rely on your monovision when you aren’t behind the wheel.