Binocular Vision and Eye Teaming, Explained

Updated 2026-10-23

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

Binocular vision means using both eyes together as a team. Your two eyes each see the world from a slightly different spot, and your brain blends those two views into one clear, three-dimensional picture. Eye care professionals call this teamwork eye teaming. When it works, you never think about it. When it does not, close work can feel tiring, words can blur or double, and headaches can build up. This guide explains what binocular vision is, the signs of poor eye teaming, the main binocular vision problems, how an eye doctor tests for them, and what the evidence says about the term binocular vision dysfunction (BVD) and microprism glasses.

What is binocular vision? What eye teaming means

EyeWiki, the American Academy of Ophthalmology's clinical wiki, describes three levels of binocular vision. The first is seeing with both eyes at the same time. The second is fusion, where the brain merges the two images into one. The third and highest is stereopsis, the fine depth perception that comes from the small differences between what each eye sees.

Several skills make this possible:

Vergence: turning the eyes in together (convergence) to look at something close, and back out (divergence) to look far away.
Fusional vergence: the reserve that keeps the two eyes locked on the same target, so you see one image instead of two.
Accommodation: focusing the lens inside the eye for close work. Focusing and turning inward are linked, so a problem with one can strain the other.
Eye movements: following a moving target and jumping accurately from one word to the next.

Eye teaming issues: common signs and symptoms

Eye teaming problems often show up during reading, screen use or other close work, and tend to get worse the longer the task goes on. Signs that EyeWiki and the American Optometric Association (AOA) list for eye teaming and focusing problems include:

Tired, sore or strained eyes during or after close work
Headaches with reading or screen use
Blurred vision up close, or blur when looking up from near to far
Double vision, or words that seem to move on the page
Losing your place while reading
Closing or covering one eye, rubbing the eyes, or avoiding close work

The main binocular vision problems

These symptoms are not specific. Needing glasses, a focusing problem and an eye teaming problem can all feel the same, which is why an exam matters. The most common binocular vision disorders include:

Convergence insufficiency (CI): EyeWiki describes it as "a decreased ability to converge the eyes and maintain binocular fusion while focusing on a near target." Our guide to convergence insufficiency exercises covers it in depth.
Phorias: a phoria is a hidden drift. The eyes stay lined up while both are open and fused, and drift only when fusion is broken, for example when one eye is covered. A phoria that is hard to control can cause strain.
Tropias (strabismus): a tropia is a turn you can see while both eyes are open. Our guide to strabismus exercises covers eye turns and when they need medical care.
Amblyopia (lazy eye): vision in one eye does not develop fully in childhood. See our guide to lazy eye exercises.
Suppression: the brain tunes out one eye to avoid double vision or a blurred image. See our guide to visual suppression.
Accommodative dysfunction: a focusing problem that the AOA says is often linked to the eyes not working together well.

How eye doctors test binocular vision

There is no single binocular vision test. An ophthalmologist, optometrist or orthoptist runs a set of short checks, usually after measuring your glasses prescription. The AOA says a comprehensive exam looks at how your eyes focus, move and work together. Common parts of an eye teaming test include: Eye care professionals who want to measure eye movements objectively can see Optics Tracker on our clinic site.

Cover test: you look at a target while the examiner covers one eye, then the other. If the uncovered eye has to move to pick up the target, that points to a tropia. Moving the cover back and forth brings out a hidden phoria. Prisms can then measure the size of the drift. Eye care professionals can read our clinician guide to binocular vision assessment.
Near point of convergence (NPC): a small target moves toward your nose until it doubles or one eye drifts out. EyeWiki treats a break point farther than 6 cm as abnormal before middle age, or farther than 10 cm once close focus naturally declines.
Fusional vergence ranges: prisms of increasing strength test how far your eyes can turn before the image doubles. EyeWiki says near convergence ranges below about 15 to 20 prism diopters suggest CI.
Stereo tests: pictures seen through polarized or colored glasses check fine depth perception. Our guide to depth perception and stereopsis explains these tests.
Worth 4 Dot: four lights seen through red-green glasses show whether both eyes are being used together.
Symptom questionnaires: for CI, the 15-item Convergence Insufficiency Symptom Survey is common. The cutoff depends on age. EyeWiki gives a score of 16 or more as a sign of CI, the cutoff used in studies of children, while a 2005 trial in adults aged 19 to 30 counted a score under 21 as symptoms being gone.

What is binocular vision dysfunction (BVD)?

If you search for binocular vision dysfunction symptoms, you will find some practices using "BVD" for something narrower: a very small vertical misalignment, where one eye aims slightly higher than the other. These practices link it to dizziness, headaches and other symptoms, and treat it with microprism glasses, lenses with a very small amount of prism. This idea is often called vertical heterophoria or vertical heterophoria syndrome.

What reviews and studies of this use report:

A 2022 consensus statement by neuro-ophthalmologists said the scientific basis for vertical heterophoria syndrome is weak. The published studies were case reports and case series without control groups, and the statement did not support vertical prisms for this diagnosis.
A 2021 review in Survey of Ophthalmology called vertical heterophoria as a cause of symptoms after mild brain injury an unproven concept, with no controlled data on vertical prisms.
A 2010 study often cited for this approach looked back at the records of 43 people with concussion symptoms and reported a 71.8% drop in self-reported symptoms after prism glasses. It had no comparison group, so it cannot show the prisms caused the change.
A placebo-controlled trial of these glasses was registered in 2008. It enrolled 13 people, was stopped because it could not recruit enough, and posted no results.
A 2026 study of 84 service members with past brain injury found small vertical misalignments were common; they were not tied to any single symptom, and had only a weak link with the total number of symptoms. The authors said treating them needs more study.

Binocular vision dysfunction treatment: what studies have tested

Treatment depends on the actual diagnosis. For convergence insufficiency, EyeWiki notes that correcting any glasses prescription comes first. For convergence insufficiency, our guide to convergence insufficiency exercises covers what the main trials found about office and home therapy, and our guide to home vision therapy explains what home programs can and cannot do.

Other binocular vision problems have different treatments. Eye turns may need glasses, prisms or surgery. Lazy eye is treated with glasses, patching, atropine drops or a cleared prescription treatment. For vertical misalignment and microprism glasses, there is no controlled trial evidence yet. If a clinician recommends prism glasses, it is reasonable to ask what was measured, what the glasses are expected to change, and how you will both judge whether they helped.

If symptoms started after a head injury, or you have sudden double vision, a new eye turn or vision loss, see an eye doctor or physician promptly. These need a medical exam, not home practice.

Where Optics Trainer fits

Optics Trainer is a set of game-based vision and brain training apps for iPhone, iPad, Android, web browsers and Meta Quest. Its games include eye teaming practice with convergence and divergence levels, binocular games where each eye gets its own target while both stay open, depth games and visual reaction games. On a phone, tablet or computer, the binocular games use red-blue glasses; on Meta Quest, the separation is built in. Optics Trainer does not test or diagnose binocular vision, it is not a treatment, it is not FDA cleared, and it was not tested in the studies described above.

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

What does eye teaming mean?

Eye teaming means your two eyes working together. They turn in or out as a pair, stay aimed at the same spot and send matching images, so your brain can blend them into one clear, three-dimensional picture.

What are the symptoms of poor eye teaming?

Common signs include eye strain, headaches with close work, blur or double vision up close, words that seem to move, losing your place while reading, and closing one eye. These can also come from needing glasses or a focusing problem, so an eye exam is the way to find the cause.

How do you test for binocular vision problems?

An eye care professional uses several short checks: a cover test for eye drifts and turns, the near point of convergence, prism tests of how far your eyes can turn together, stereo tests for depth perception, and sometimes a symptom questionnaire. There is no single test, and an online check cannot replace this exam.

Is binocular vision dysfunction a real diagnosis?

Binocular vision problems such as convergence insufficiency and strabismus are well established. Some practices use "BVD" to mean a tiny vertical misalignment treated with microprism glasses. A 2022 neuro-ophthalmology consensus statement said its scientific basis is weak and that the studies lacked control groups.

Do microprism glasses work for BVD?

There is no controlled trial showing they do. The main supporting study looked back at 43 patient records without a comparison group, and a placebo-controlled trial was stopped after enrolling 13 people, with no results posted.

Why are my eyes not teaming together?

Common reasons include convergence insufficiency, a hidden drift (phoria) that is hard to control, an eye turn, lazy eye, a focusing problem or an uncorrected glasses prescription. Eye teaming can also be affected after a concussion. A comprehensive eye exam with binocular vision testing can tell these apart.