Vision therapy is designed to improve how the eyes and brain work together, but what actually changes in the brain? Researchers have used MRI and other brain-imaging techniques to study how visual processing may change after vision therapy. The findings offer some evidence of neurological changes, but they also have important limitations.
This article looks at what vision therapy neurological research has shown, what the major clinical trials tell us about vision therapy, and where the current evidence still falls short. It also explains how Dr. Kelly Lee, OD, FAAO, FOVDRA, owner and lead optometrist at Tonic Eye Care, approaches vision therapy in Midtown Toronto.
Why Is Brain Research Important to Vision Therapy?
Vision therapy neurological research looks at how visual processing may change with training and experience. Neuroplasticity refers to the brain’s ability to change in response to experience and repeated activity. Because vision depends on coordinated processing between the eyes and brain, researchers have studied whether visual function can change with training.
Some of the foundational evidence for experience-dependent changes in the visual system came from David Hubel and Torsten Wiesel, who shared the 1981 Nobel Prize in Physiology or Medicine. In experiments with kittens, they found that covering one eye during an early period of development affected how the visual cortex responded to that eye. The same type of deprivation in adult cats did not produce the same changes. This work helped establish the concept of a critical period in visual development.
Later research has shown that the adult visual system may retain some capacity for change. A 2023 review in the European Journal of Ophthalmology by Benjamin Thompson and colleagues discusses evidence that some visual plasticity can persist beyond childhood. Studies of adults with amblyopia have also reported improvements in visual function under certain conditions.
This research provides a basis for studying whether visual training can produce changes in visual processing, but it does not by itself prove that vision therapy causes specific changes in the brain. That question requires clinical and neuroimaging studies in people undergoing vision therapy.
How Does the Brain Build One Picture From Two Eyes?
Visual information travels from the retina through the optic nerves and optic chiasm before reaching the brain’s visual processing areas. Signals from both eyes are eventually processed together, allowing the brain to compare the two images and create a single view of the world. This coordination is important for binocular vision and depth perception.
Four terms come up in the research on vision therapy:
- Vergence is the movement of the eyes inward or outward so they can aim at the same point. Convergence is the inward movement used for near tasks such as reading.
- Accommodation is the eye’s ability to change focus so a near object appears clear.
- Fusion is the brain’s process of combining the images from both eyes into one.
- Suppression occurs when the brain reduces or ignores input from one eye, which can help prevent double vision.
Convergence insufficiency is one of the most studied binocular vision conditions in vision therapy research. The eyes can converge, but they may not converge enough or maintain that position comfortably for near tasks. Reading can then cause symptoms such as eye strain, headaches, blurred or moving words, and difficulty concentrating. It is one of several eye-teaming conditions covered under binocular vision dysfunction treatment at Tonic Eye Care. Tonic Eye Care’s convergence insufficiency symptom survey uses the same 15-question Convergence Insufficiency Symptom Survey used in major clinical trials.
What Do Brain Scans Show in Vision Therapy Neurological Research?
Functional MRI, or fMRI, measures changes in blood flow and oxygen use in the brain while a person performs a task. Researchers can use these changes to see which brain regions are more or less active during visual tasks. Tara Alvarez’s lab at the New Jersey Institute of Technology has used fMRI to study the neurological side of convergence insufficiency and vision therapy.
| Study | Who was scanned | What changed | Main limit |
|---|---|---|---|
| Alvarez et al., Optometry and Vision Science, 2010 | 4 adults with convergence insufficiency, 13 controls | After 18 hours of therapy, activity increased in the frontal eye fields, cerebellum and brainstem; symptom scores also improved | Four patients and no placebo group |
| Alvarez et al., Scientific Reports, 2021 | 50 adults with convergence insufficiency, 50 controls | Before treatment, patients showed slower convergence and differences in activity in the cuneus and oculomotor vermis | Shows an association, not a treatment effect |
| Sangoi et al., Frontiers in Neuroscience, 2025 (CONCUSS trial) | 54 people aged 11 to 25 with concussion-related convergence insufficiency, 46 controls | After vision therapy, activity changed in visual area V3 and the cerebellar vermis; clinical measures also improved | Longer-term follow-up was limited |
| Barberán-Bernardos et al., Journal of Ophthalmology, 2024 (systematic review) | 4 studies, 84 participants in total | Changes were reported in frontal, parietal, cerebellar and brainstem regions across studies | Certainty of evidence was rated very low |
The 2010 study was very small: four women in their twenties were scanned before and after six weeks of office-based and home therapy. Their near point of convergence, the closest distance at which they could maintain a single image, improved from 13.4 cm to 8.1 cm. Because there were only four patients and no placebo group, the study could not establish whether the observed brain changes were caused by the therapy.
The 2021 study looked at people with convergence insufficiency before treatment. Compared with controls, they showed slower convergence and differences in activity in the cuneus, a visual-processing region at the back of the brain, and the oculomotor vermis of the cerebellum. This study is useful for understanding how convergence insufficiency may differ neurologically, but it does not show what happens after vision therapy.
The 2025 CONCUSS results provide newer evidence from people aged 11 to 25 with concussion-related convergence insufficiency. After vision therapy, the near point of convergence improved from 10.4 cm to 3.1 cm, and researchers reported changes in activity in areas including visual area V3 and the cerebellar vermis. Greater changes in some brain measures were also associated with greater clinical improvement.
The 2024 systematic review brought the available neuroimaging studies together and rated the certainty of the evidence as very low. The review highlighted small sample sizes, different treatment protocols and inconsistent findings between studies. One study reported decreased activity in some regions where others reported increases. The authors concluded that the available research is not strong enough to confirm that vision therapy causes specific changes in the brain.
The research is promising, but the distinction matters: brain scans show that visual processing can differ in people with convergence insufficiency and may change after therapy. They do not yet establish exactly why those changes occur or prove that the changes themselves are responsible for clinical improvement.
What Did the Large Randomized Trials Prove About Vision Therapy?
Brain scans can help researchers understand how a treatment might affect the visual system. Randomized clinical trials test whether the treatment improves clinical measures compared with a control or placebo treatment. Convergence insufficiency has been studied in several major randomized trials.
- The Convergence Insufficiency Treatment Trial, published in Archives of Ophthalmology in 2008, randomized 221 children aged 9 to 17 to office-based therapy, two types of home-based exercises or office-based placebo therapy. After 12 weeks, 73% of children in the office-based therapy group met the study’s definition of success, compared with 35% in the placebo group and 43% in the pencil push-up group.
- The CITT-ART trial, published in Optometry and Vision Science in 2019, randomized 311 children aged 9 to 14 to 16 weeks of office-based therapy or placebo therapy. Near point of convergence improved by 10.4 cm with therapy compared with 6.2 cm with placebo, while fusional vergence range improved by 23.2 prism dioptres compared with 8.8. However, symptom scores improved by similar amounts in both groups.
- The CINAPS trial, published in Optometry and Vision Science in 2020, used a similar design in 50 adults aged 18 to 32. Measures of convergence improved more with office-based therapy than with placebo, while symptom scores again improved by similar amounts between groups.
Taken together, these trials provide evidence that office-based vision therapy can improve some clinical measures of convergence function beyond placebo treatment. The results for symptoms are less clear, since people in both the therapy and placebo groups often reported feeling better.
That distinction matters when evaluating the evidence. Clinical measurements such as near point of convergence and fusional vergence can show whether a specific visual function has changed, while symptom questionnaires capture how the patient feels. Both are useful, but they measure different things. Tonic Eye Care describes its approach to tracking these measures in its evidence and outcomes guide to vision therapy.
Can Amblyopia Be Treated After the Critical Period?
Amblyopia, often called lazy eye, is reduced vision in one eye that is not fully corrected by glasses and develops when the brain favours the other eye during childhood. It has become an important area of research into whether visual plasticity can continue beyond the traditional critical period.
Researchers have studied approaches such as perceptual learning, which uses repeated visual tasks to train the weaker eye, and dichoptic training, which presents different images to each eye with the goal of reducing suppression.
The results have been mixed. In a 2016 trial from the Pediatric Eye Disease Investigator Group, 385 children were randomized to a binocular iPad game or patching. After 16 weeks, visual acuity improved in both groups, but the binocular game did not meet the study’s criteria for being as effective as patching. Only 22% of children played the game as often as prescribed, which also limited the study’s interpretation.
A 2023 review by Thompson and colleagues similarly found promising but inconsistent evidence for binocular approaches. A Cochrane review also concluded that there was not enough evidence to establish lasting benefits.
The research suggests that some visual plasticity may remain after childhood, but it does not mean that every vision problem can be retrained. The strength of the evidence varies considerably by condition.
How Does Tonic Eye Care Apply This Research?
Dr. Kelly Lee, OD, FAAO, FOVDRA, completed a residency in vision therapy, vision rehabilitation and pediatric care and is a Fellow of the American Academy of Optometry. At Tonic Eye Care, she uses clinical evidence as the starting point and treats brain-imaging research as an area of ongoing study. Progress is assessed through measurable changes in visual function, along with the symptoms and concerns that brought the patient in.
Tonic Eye Care’s programs use weekly in-office sessions supported by home practice. Children begin with a developmental vision evaluation through the kids vision therapy program. The vision therapy service page explains the conditions the clinic treats and those it does not, including learning disabilities and ordinary refractive errors such as nearsightedness and astigmatism.
Frequently Asked Questions
Is there scientific evidence that vision therapy works?
Yes, particularly for convergence insufficiency. Randomized clinical trials have found that office-based therapy improves measures of eye teaming more than placebo therapy in children and adults. Evidence for amblyopia and strabismus is more mixed. Research does not support vision therapy as a treatment for dyslexia or as a way to improve reading skills.
How does neuroplasticity relate to vision?
Neuroplasticity is the brain’s ability to change in response to experience and repeated activity. Because vision involves coordinated processing between the eyes and brain, researchers have studied whether visual training can produce changes in this system. Small fMRI studies have reported changes in brain activity after vision therapy, although a 2024 systematic review rated the certainty of this evidence as very low.
Am I too old to benefit from vision therapy?
No. Adults can benefit from vision therapy for convergence insufficiency. A 2020 randomized trial in adults aged 18 to 32 found greater improvements in convergence measures with office-based therapy than with placebo. Research into adult amblyopia is less conclusive, with studies of perceptual learning and dichoptic training showing some improvement but mixed results.
Does vision therapy treat dyslexia?
Vision therapy is designed to treat visual dysfunctions, not learning disabilities like dyslexia. However, resolving an underlying eye-teaming issue can remove a major barrier to reading comfort. A child with reading or attention difficulties should still have a comprehensive eye exam to identify any separate vision or eye-teaming problem.
Is vision therapy recommended?
The strongest clinical evidence is for symptomatic convergence insufficiency and some accommodative problems. Whether vision therapy is appropriate depends on the child’s or adult’s specific diagnosis and symptoms. Tonic Eye Care assesses patients before recommending therapy and can identify situations where it is unlikely to help.
