Red Green Glasses in Vision Therapy: How They Work

Updated 2026-10-23

Written by the Optics Trainer team from published research, with every source linked below. Not yet reviewed by a clinician.

If your child came home from an eye appointment with a pair of red-green or red-blue glasses, you may be wondering what they do. These glasses are a simple tool. Each lens is a color filter, so each eye sees different parts of a picture, a chart or a game. Eye care professionals use them to check whether both eyes are working together and, in vision therapy, to make the weaker eye do more of the work while both eyes stay open. This guide explains how red green glasses work, what activities like MFBF and anti-suppression exercises are, and what the research does and does not show. Some red-green and red-blue treatments have been tested in randomized trials, while classic anti-suppression activities have mostly been studied in small or non-randomized studies.

Why kids wear red-green or red-blue glasses in vision therapy

When the two eyes do not team well, the brain can start to tune out, or suppress, one eye. This often goes with a lazy eye (amblyopia) or an eye that turns (strabismus). Suppression can be hard to notice, because the child still sees with the other eye.

Colored filter glasses, also called anaglyph glasses, let an eye care professional show each eye something different. That helps with two jobs. The first is testing: seeing whether a child is using both eyes at once. The second is practice: setting up activities where the weaker eye has to do part of the task while the stronger eye stays open.

The glasses do not treat anything on their own. What matters is the test or activity they are used with, and whether that activity has evidence behind it.

How do red green glasses work?

Each lens blocks the other color. A red lens blocks green light, and a green lens blocks red light. So an eye behind the red lens cannot see green marks, and an eye behind the green lens cannot see red ones. White marks can be seen by both eyes. Red-blue glasses work the same way with a different pair of colors.

The classic example is the Worth 4 Dot test, described in EyeWiki, the American Academy of Ophthalmology's clinical wiki. The child wears red-green glasses, usually with red over the right eye, and looks at four lights: one red, two green and one white. What the child reports tells the examiner how the eyes are working: Eye care professionals can read our clinician articles on the Worth 4 Dot test and anaglyph glasses in vision therapy.

4 dots: both eyes are being used together (in a child with a visible eye turn, the examiner reads this result differently).
2 red dots: the left eye is being suppressed.
3 green dots: the right eye is being suppressed.
5 dots: the child is seeing double.

MFBF and anti-suppression vision therapy activities

Anti-suppression activities aim to help the brain notice the eye it has been ignoring. In a PEDIG pilot study of vision therapy for amblyopia, the anti-suppression steps included a Brock string, a long string with beads, and drawing with anaglyph glasses.

MFBF stands for monocular fixation in a binocular field. The term appears in optometry journals at least as far back as 1981. The idea is that both eyes are open, but only one eye can see the target. In a 2015 Optometry Times article, an optometrist described an MFBF matching game. The child wears red-green glasses and matches tiles to targets laid over a red sheet, so each eye sees only one set of pictures. If the child cannot see one set, or the targets start to disappear, the author says that is a sign of suppression. The author disclosed a financial interest in this game.

A 2024 study described MFBF as a way to make the weaker eye work with the other eye without a patch. Some programs run MFBF tasks on a computer, such as the software tested in a 2020 study described below.

Red green glasses for lazy eye: what the game trials found

Several binocular treatments for amblyopia were tested with red-green or red-blue glasses. In the iPad games, the stronger eye sees lower-contrast parts of the game and the weaker eye sees higher-contrast parts, so both eyes are needed to play. CureSight instead blurs the center of the picture for the stronger eye. What the trials found:

In a small 2016 trial of 28 children aged about 4 to 9, an iPad game played with red-green glasses improved vision more than patching after 2 weeks.
In a larger 2016 PEDIG trial of 385 children aged 5 to 12, an iPad game played with red-green glasses for 1 hour a day did not match 2 hours of daily patching. Only 22% of children in the game group did more than three-quarters of their assigned play.
In two PEDIG trials of a game called Dig Rush, also played with red-green glasses, the game added no benefit over glasses alone in children aged 7 to 12. In children aged 4 to 6, it helped a little at 4 weeks, but the difference was gone by 8 weeks.
CureSight, an FDA-cleared prescription treatment for children aged 4 to under 9, uses red-blue glasses plus an eye tracker while a child watches videos. In a trial of 103 children, 90 minutes a day, 5 days a week, for 16 weeks was found noninferior to 2 hours of daily patching, meaning it was not meaningfully worse.
A 2022 Cochrane review found only one eligible trial comparing binocular treatment with patching in young children and said firm conclusions were not yet possible.

Do vision therapy glasses work? What MFBF and anti-suppression studies found

We did not find a large randomized trial showing that home MFBF or anti-suppression exercises improve vision in a lazy eye.

PEDIG tried to run a trial that added office-based vision therapy, including anti-suppression work, to daily patching for children aged 7 to 12 with amblyopia. It enrolled only 19 children and was stopped because too few could be recruited. The team also had trouble collecting data on home practice.
A 2020 pilot study of 54 children with amblyopia from unequal glasses prescriptions found that an MFBF computer program was not better than patching; the difference between groups was not statistically significant.
In a 2024 study of 65 children that was not randomized, a vision therapy program that included anti-suppression and MFBF improved depth perception more than patching, but not sharpness of vision. The authors said randomized trials are needed.
For a different condition, intermittent exotropia, where an eye sometimes drifts outward, a 2024 trial of 40 children found that office-based vergence and anti-suppression therapy improved eye control at 17 weeks compared with watching and waiting. The authors called for a larger, longer trial.

Using red-blue glasses at home: what to ask your eye doctor

Red-green and red-blue activities are usually one part of a plan from an ophthalmologist, optometrist or orthoptist, often alongside glasses or patching. Before starting at home, it helps to ask:

What condition are we treating, and is suppression part of it?
Is a prescribed treatment, such as patching, atropine drops or a cleared dichoptic treatment, a better first step?
Which glasses should we use, and which eye goes behind which color?
How many minutes a day, and when will you recheck vision?
What should we do if my child sees double, gets headaches or says the targets keep disappearing?

Where Optics Trainer fits

For more on lazy eye treatment, see our guides to lazy eye exercises and VR lazy eye treatment. For eye turns, see our guide to strabismus exercises.

Optics Trainer is a set of game-based vision and brain training apps for iPhone, iPad, Android, web browsers and Meta Quest. Its binocular games give each eye its own target while both eyes stay open. On a phone, tablet or computer, you wear red-blue glasses for these games; on Meta Quest, the separation is built in. It is a way to practice visual skills at home. Optics Trainer is not a treatment or diagnosis for amblyopia or strabismus, it is not FDA cleared, and it was not tested in the studies described above. It is not an alternative to a prescribed treatment such as patching or CureSight.

Optics Trainer is not a substitute for professional diagnosis or prescribed care. Consult your eye care professional for guidance about your specific condition. If your clinician agrees that home practice fits alongside your plan, mobile and web access is $14.99 a month or $149.99 a year. The phone and tablet apps start with a 7-day free trial, and a free web account includes 3 plays a day. VR access is $19.99 a month or $199 a year after a 7-day free trial.

Frequently asked questions

How do red green glasses work for vision therapy?

Each lens is a color filter that blocks the other color, so each eye sees different marks on a chart, card or screen. That lets an eye care professional check whether both eyes are working together, or set up activities where the weaker eye has to do part of the task.

Do red green glasses help lazy eye?

Not on their own. Some games and video treatments that use colored glasses have been tested. One, CureSight, was found noninferior to (not meaningfully worse than) patching in its trial, but in larger trials two iPad games did not match patching or beat glasses alone.

What is MFBF in vision therapy?

MFBF stands for monocular fixation in a binocular field. Both eyes stay open, but filters make the target visible to only one eye, usually the weaker one. In a 2020 pilot study of 54 children, an MFBF computer program was not better than patching.

What are anti-suppression exercises?

They are activities meant to help the brain stop tuning out one eye, such as a Brock string or drawing while wearing colored filter (anaglyph) glasses. They are used in vision therapy, but we found no large randomized trial showing they improve vision in a lazy eye at home.

What is the red and green dot test at the eye doctor?

It is probably the Worth 4 Dot test. Your child wears red-green glasses and looks at four lights. Seeing four lights suggests both eyes are being used together. Seeing two, three or five can point to one eye being suppressed or to double vision.

Are red blue glasses the same as red green glasses?

They work on the same idea, with a different pair of colors. Each lens blocks the color of the other, so each eye sees different things. Use the glasses your clinician or program specifies, and ask which eye goes behind which color.