Dictionary of terms relating to
eyesight and vision

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A three-dimensional picture that is used to strengthen the binocularity system. Available in fixed and variable styles to provide base-in and/or base-out training. 3D glasses are used to view the picture.


To turn the eyes horizontally (convergence- inward or divergence- outward). Accommodative vergence, fusional vergence, proximal vergence, and tonic vergence are needed to maintain single vision.

Vergence Facility

A measure of the ease and speed of the eyes to change from a converging to diverging position.


A disordered state in which the individual is dizzy or feels that the surrounding environment is whirling.

Visagraph Eye-Movement Recording System

Records and measures eye movements while an individual reads. The system also measures reading efficiency. Specially created goggles and a computer program are used.


The ability to take in information through our eyes and process the information so that it has meaning.

Vision Therapy (VT)

See "Optometric Vision Therapy"

Vision Therapy Technician

One who works under the supervision of an optometrist in evaluating clients and in planning and implementing vision therapy programs.

Vision Therapist

Optometrist or an optometric vision therapy technician who develops and administers vision therapy programs. (Typically this term is referring to a vision therapy technician rather than an optometrist.)

Please note that there are some individuals that call themselves vision therapists, but they are not optometrists or vision therapy technicians.

Visual Acuity

Sharpness or clearness of eyesight. For more information see "Near Acuity" and "Distance Acuity", "20/20"

Visual Acuity Test

This test is the most basic test performed during a routine eye examination and tells you how well you can see objects from a distance. If you can see letters that are approximately one inch high from 20 feet away you have 20/20 vision. This is considered to be "normal" visual acuity. When you have 20/40 vision it means that you need to be 20 feet away to see what a person with normal visual acuity can see from 40 feet away. Keep in mind that your visual acuity may change depending on what time of day you have the test.

The doctor will ask you to read rows of letters that are 20 feet away from you. If the examination room has limited space the doctor will use mirrors to make the letters appear 20 feet away.

Normal Range of Results
"Normal" vision is 20/20. Though some states are more lenient, in most states your corrected vision must be 20/40 or better in at least one eye to pass a driver's licensing test.

Visual Analysis

Refers to figure-ground, form constancy, spatial relation, visual closure, visual discrimination, visual memory, and visualization.

Visual Closure

The ability to identify or recognize a symbol or object when the entire object is not visible.

Visual Discrimination

The ability to discriminate between visible likeness and differences in size, shape, pattern, form, position, and color. Such as the ability to distinguish between similar words like "ran" and "run".

Visual Field

The total area that can be seen while looking straight ahead. (See "Tunnel Vision".) (Note: Perimetry is the method of testing an eye's field of vision. For more information, please see "Perimetry".)

Visual Form Dysfunction

Difficulty with figure-ground, form constancy, visual closure, and visual discrimination. Symptoms include confusion with similar objects, words, or colors. Vision therapy is a treatment option.

Visual Memory

The ability to recall and use visual information from the past. (See "Visual Sequential Memory")

Visual Memory Dysfunction

Difficulty with retention, recall, or recognition of things seen. Symptoms can include poor spelling and poor recall of visual information. Vision therapy is a treatment option.

Visual-Motor Dysfunction

The inability to process and reproduce visual images by writing or drawing. Symptoms can include poor pencil grip/writing, poor organization on written page, poor copying/spacing, and excessive erasing. Vision therapy is a treatment option.

Visual-Motor Integration (VMI

After visual data is gathered, it is processed and combined in the brain with information from movement (eye hand coordination).

Visual-Motor Skills

The ability of our eyes to guide our hands (eye hand coordination, visual-motor integration).

Visual Pathway

Route of the nerve impulses from the retina along the optic nerve, and optic nerve radiations to the brain's sensory cortex that is located at the base of the skull.

Visual Perceptual Disorders

Information processing dysfunctions of the visual system. These dysfunctions can be a directionality/laterality disorder, visual form dysfunction, visual memory dysfunction, and visual-motor dysfunction. Vision therapy is a treatment option. (Also see "Perceptual Skills")

Visual Perceptual Skills

The ability to organize and interpret information that is seen and give it meaning. These information-processing skills include figure-ground, form constancy, spatial relations, visual closure, visual discrimination, visual memory, and visualization.

Visual-Sensory Integration

After visual data is gathered, it is processed and combined in the brain with information from hearing (auditory-visual integration), balance (gross-motor/bilateral integration), posture, and movement (visual-motor integration).

Visual Sequential Memory

Ability to recall a sequence of numbers, letters or objects in the order they were originally given.

Visual Skills

Are accommodation (eye focusing), binocularity (eye teaming), and oculomotor skills (eye movement), which are neuro-muscular abilities that are controlled by muscles inside and outside of the eye and are networked with the brain.


The ability to crate and manipulate mental pictures of an object or concept on the basis of past visual experience and memory. Essential in reading and playing sports.