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Vision Therapy Glossary

Explore the vision therapy glossary terms and definitions below.



Also known as focusing ability, the eye’s ability to change focus from one distance to another and maintain focus at close distances. Symptoms of a focusing problem include blurred vision during reading or copying, eye strain, headache, fatigue and difficulty with reading comprehension. Presbyopia is an accommodative disorder that affects everyone as they become older and is why reading glasses and bifocals are necessary as we age.

Acuity (Clarity of Sight)

The ability to see clearly at near and far distances, expressed as 20/20, 20/40 etc. Visual acuity only refers to the ability to see small images and does not predict how well the eyes work together, focus, track or interpret what is seen.


Also called lazy eye. Leading cause of vision loss in children. Undeveloped or reduced vision in one eye that is not correctable with glasses. Caused by strabismus, unequal amounts of refractive power between the 2 eyes or high amounts of farsightedness, nearsightedness, or astigmatism in both eyes. Amblyopia can be treated with patching therapy, eye drops or vision therapy, and can be treated effectively even beyond childhood.


Condition where the eyes have a significantly different refractive power from each other. Often results in amblyopia and suppression without treatment.


A refractive error where objects have a distorted appearance due to the cornea (outside layer of the eye) being misshapen. Causes distance and near blurred vision as well as eyestrain but is usually correctable with glasses or contact lenses.

Binocular vision

Ability of both eyes to work together as a team that allows normal depth perception and clear comfortable single vision. Binocular vision problems cause headaches, eye strain, double vision, blurred vision and loss of place especially during reading and close work. Reading comprehension can also be affected. More significant binocular vision problems include strabismus where the eyes appear misaligned all or part of the time.


A brain injury resulting from a blow to the head or a whiplash that causes rapid deceleration or acceleration of the brain. Concussion causes cellular damage in brain networks and has a variable recovery. Typical post-concussion symptoms can include a range of vision deficits, vestibular and balance issues, headaches, and cognitive, sleep and emotional issues.


Eyes’ ability to cross or turn inwards towards the nose during any close visual activities such as reading or computer use.

Convergence Insufficiency

The most common eye teaming disorder. Causes eye strain, double vision, headaches, blur and loss of place with reading and close work. Children with convergence insufficiency are at higher risk of being diagnosed with ADHD.

Convergence Excess

A common eye teaming disorder where the eyes have a tendency to cross too much during reading and close work. Causes eye strain, double vision, headaches, blur and loss of place during close visual activities.

Developmental or Behavioral Optometrist:

A Developmental or Behavioral Optometrist diagnoses and treats vision disorders that affect development, learning, behavior and functional uses of the visual system. Most Developmental Optometrists offer vision therapy services and are often board certified by the College of Optometrists in Vision Development (COVD.org).


Eyes ability to turn outward in a coordinated fashion as when we look from near to far.

Diplopia or Double Vision

When two images of the same object are perceived by one or both eyes. Can look like words are moving or running together during reading. Usually the result of binocular vision (eye teaming) problems.


When the eyes have a tendency to cross inwards towards the nose but do not actually become misaligned. The effort involved in keeping the eyes working together as a team can cause headaches, eye strain, or double vision especially during reading and close work.

Esotropia When one or both eyes are misaligned and point inward, so the eyes are “crossed.” This is one type of strabismus.


When the eyes have a tendency to drift outwards towards the ears but do not actually become misaligned. The effort involved in keeping the eyes working together as a team can cause headaches, eye strain, or double vision especially during reading and close work.

Exotropia When one or both eyes are misaligned and point outward; also called a drifting or wandering eye. This is one type of strabismus.


The ability of the brain to combine the input from each eye into single vision. When fusion can’t be maintained, double vision will occur or one eye must be suppressed in order to avoid double vision.


Also called farsightedness. A refractive error where extra focusing effort is needed to see distance and near objects clearly. Depending on age and degree of hyperopia, objects may be clear or blurred without glasses. Other symptoms of hyperopia include headaches, eye strain, and avoidance of reading and other near tasks. Can also affect pre-school vision development.


Also called nearsightedness. A refractive error where near objects are seen clearly but distance vision is blurred. Myopia typically begins in childhood and progresses during the school years. Squinting is the primary sign of myopia in early childhood.


Rapid and involuntary eye movement where the eyes oscillate either slowly or quickly. Blurred vision usually results. Nystagmus typically appears in infancy.

Oculomotor Dysfunction

Another term for eye tracking difficulty. Also known as deficiencies of pursuits and saccades.


Individuals who are trained to make and fit glasses. Opticians are not licensed to write prescriptions for glasses or to perform eye examinations.

Optometrists (O.D.)

Doctors of Optometry who have attended 4 years of optometry school after college to study the eye and visual system. They can perform eye examinations, fit contact lenses, provide vision therapy and treat various eye diseases with topical and systemic medications. They do not perform ocular surgery.

Ophthalmologist (M.D.)

Physicians who have completed a residency in the treatment of eye disease after medical school. They perform eye examinations and treat eye disease with medications and surgery.


A term for a limited form of vision therapy originally developed for strabismus.


A type of prescription lens that can help lessen double vision as well as impact visual spatial perception.

Pursuit Eye Movements

The ability to maintain your eyes on a moving object by moving the eyes at the same speed as the object, regardless of any changes in head or body posture. Important in sports and eye-hand coordination.

Saccadic Eye Movements

Also known as visual tracking. Saccades are small eye movements used when jumping from one word to another along a line of print or scanning objects in the environment. They are a developed fine-motor skill. Problems with saccadic eye movements cause loss of place with reading, omitting and substituting words, skipping lines, and reduced reading speed, as well as slow or inaccurate copying.


Also known as depth perception, it is the result of binocular fusion and allows us to see a three dimensional world. Amblyopia, strabismus and eye teaming problems often cause reduced stereopsis.


The cancellation or shutting off by the brain of the visual signals from one eye to prevent double vision and confusion that arise from binocular vision problems. Suppression causes reduced depth perception and in young children can also lead to amblyopia. Suppression is reversible with vision therapy.

Visual Processing

Visual processing, or visual perception, is the brain’s ability to analyze, interpret and output visual information. Visual processing is important in letter and number recognition, early reading and math skills, handwriting, and the ability to copy and organize written work. It includes such visual skills as visual-spatial ability, directionality, discrimination, closure, figure-ground, visual-motor integration, and processing speed.

Visual-Motor Integration (VMI) Dysfunction

The inability of the mind’s eye to guide the hands accurately during motor tasks. Children with VMI deficits struggle with handwriting, copying, drawing, organizing written output on paper, and answer sheets. Gross motor tasks can also be affected. Occupational therapists will often diagnose visual-motor problems in a school setting.

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