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Vision Defects and Vision Restoration Therapy – Glossary of Common Terms

It is easy to become confused by the array of terms used to describe vision, vision loss, and vision rehabilitation after a stroke or a brain injury. NovaVision has prepared this list of definitions to help educate both patients with vision loss and those who care for them.

Glossary A-B


Eye focusing; the eye’s ability to adjust its focus from far to near by the action of the ciliary muscle this increases, or decreases the focusing power of the lens and helps maintain clear vision at all distances. Accommodation usually and naturally stops in middle age.


Clarity of vision. Depends on the sharpness of images and the sensitivity of nerve elements in the retina.

Advanced Care Center

A medical center with special expertise in VRT that is available to treat patients with special needs or desiring more medical or functional attention.


The proper fusing (uniting) of images to each eye provides a single clear image.

Arteriovenous Malformation (AVM)

A congenital, or developed disorder occurring in the brain or spinal cord characterized by an abnormal development of a complex, tangled web of arteries, and veins. The most common symptoms of AVM include hemorrhaging (bleeding), seizures, headaches, and neurological problems such as paralysis, loss of speech, memory loss, or visual field defects.


The brain’s ability to blend the visual images of both eyes into one three dimensional perception.

Brain Abscess

Can result from direct extension of a cranial infection (e.g., osteomyelitis, mastoiditis, sinusitis, and subdural empyema from penetrating head wounds or bacterial infections) May produce brain swelling leading to visual field defects.

Brain Tumor

An expanding benign or metastatic (i.e., spread from another location) intracranial mass that may be a granuloma, a parasitic cyst, a hemorrhage (intracerebral, extradural, or subdural), an aneurysm, an abscess, or a neoplasm (metastatic or primary). Any of these conditions can produce visual field defects. Intracranial neoplasms include craniopharyngioma, chordoma, germinoma, teratoma, dermoid cyst, angioma, and hemangioblastoma.

Glossary C-G

Cerebral Aneurysm

A weak bulging spot on the wall of a brain artery that develops gradually, often as a result of an injury, an infection, or heredity. In shape, a cerebral aneurism resembles a thin balloon or a weak spot on an inner tube. Many aneurysms never produce symptoms; however, a ruptured brain aneurysm will often produce various neurological symptoms, including visual field defects.

Cognitive Disorder

A disorder that affects people’s ability to either interpret what they see and hear or to connect information from different parts of the brain. Cognitive disorders can be divided into broad categories: speech and language disorders, memory disorders, motor disorders, visuospatial disorders, attention/concentration disorders, and planning and behavior monitoring disorders.

Color Vision Deficiency (Color blindness)

An inability to distinguish certain colors or a defect in how colors are perceived.

Constriction (Tunnel Vision)

A loss of peripheral vision that leaves only a central area of functional vision in one or both eyes.


The ability to coordinate the movements of both eyes by turning them inward to maintain single vision on a near object.


A benign slow-growing brain tumor often located near the optic chiasm which may or may not produce endocrine, visual field defects, or psychological disorders.

Depth Perception (Stereopsis)

The ability to judge the relative distances of objects. Proper depth perception is important to balance and coordination.

Diffuse Field Defects

Scattered spots or areas of decreased or lost vision in one or both eyes.

Diplopia (Double Vision)

A condition in which a single object is perceived as two images rather than one.


The ability to coordinate the movements of both eyes by turning them outward to focus on distant objects.


The ability to direct and maintain steady visual attention on a target.

Founding Center

One of the original top medical institutions to offer NovaVision Vision Restoration Therapy.


The union of images from each eye into a single image.


A variable degenerative disease of the optic nerve caused by a combination of pressure within the eye, circulatory problems, and genetic predisposition. As the optic nerve deteriorates, blind spots initially develop in the peripheral field of vision, followed by central vision loss and sometimes progressing to blindness.

Glossary H-M

Head Injury

Also referred to as traumatic brain injury, closed head injury, or penetrating head injury. Frequently produces visual field defects. Head injury may result in cerebral contusion, acute and chronic subdural hematomas, epidural hematomas, and post-traumatic epilepsy. Visual field defects caused by a head injury may be treatable with NovaVision Vision Restoration Therapy.


Decreased or lost vision in one half of the visual field in one or both eyes. Treatable with NovaVision Vision Restoration Therapy.

Hypothalamic-Pituitary Disorders

Patients with hypothalamic-pituitary disorders will experience some combination of:

  • Symptoms or signs of a mass lesion (e.g., headaches or visual field defects)
  • Hypersecretion or hyposecretion of one or more pituitary hormones

These masses frequently compress the optic chiasm, producing bitemporal hemianopias.

Intracerebral Hemorrhage

Usually results from the rupture of a blocked artery that has been exposed to hypertension for a long period of time or made ischemic by local thrombosis. Less often, the cause is a congenital aneurysm or other vascular malformation.


Intracranial Neoplasm

Brain tumor – an expanding benign or metastatic (i.e., spread from another location) intracranial mass that may be a granuloma, a parasitic cyst, a hemorrhage (intracerebral, extradural, or subdural), an aneurysm, an abscess, or a neoplasm (metastatic or primary). Any of these conditions can produce visual field defects. Congenital primary intracranial neoplasms include craniopharyngioma, chordoma, germinoma, teratoma, dermoid cyst, angioma, and hemangioblastoma.



The colored part of the eye located between the lens and cornea; regulates the entrance of light.



The part of the retina dedicated to activity and detail, about the size of a pinhead; where our most detailed vision occurs.


Macular Degeneration (AMD)

A deterioration of the central portion of the retina known as the macula.


Also called microtropia, monofixation syndrome, and small-angle strabismus. A small-angle deviation (most commonly inward but outward as well) of less than five degrees with some amount of stereopsis (depth perception) and anomalous retinal correspondence (ARC).

Multiple Endocrine Neoplasia – Type 1 (Wermer’s Syndrome)

A syndrome characterized by tumors of the parathyroid glands, the pancreatic islet cells, and the pituitary gland that may produce visual field defects.


Multiple Sclerosis

A slowly progressive, or sporadic disease of the nervous system characterized by disseminated patches of demyelination in the brain and spinal cord, resulting in multiple and varied neurologic symptoms, including visual field defects, usually with remissions and exacerbations.

Glossary N-O

Near Point of Convergence (NPC)

The closest point at which the two eyes can maintain fixation on a single target.


A physician who specializes in the treatment of patients with disease processes and injuries involving the nervous system.


Any of the conducting cells of the nervous system.



The brain’s ability, at the level of the neuron, to recover structurally and or functionally after injury or disease.

NovaVision Vision Restoration Therapy

Vision therapy intended for the diagnosis and improvement of visual function in patients with impaired vision resulting from traumatic brain injury, stroke, inflammation, surgical removal of brain tumors, or brain surgery.


The blocking out of light. An eye can be completely or partially blocked. This technique is used to promote improved visual capabilities of the unblocked eye.

Ocular Motility

Pertaining to binocular alignment and eye muscle movement: The extent to which a person can correctly move their eyes in each direction of gaze.

Ocular Motor (OM)

General eye movement ability, which includes pursuits (visually tracking and/or following moving objects) and saccades (directing and coordinating eye movement as both eyes quickly and voluntarily shift from one target to another).

Optic Atrophy

Optic atrophy is a sign of previous optic nerve disease and is not a diagnosis in itself; its presence demands a search for its cause. Dramatic return of vision can accompany reversal of certain pathologic processes (e.g., central vision and visual field defects may return after relief of pressure on the optic nerve caused by a tumor).

Optic Glioma

A mass (astrocytoma) created by the growth of abnormal nerve cells, or an uncontrolled proliferation of cells, in one optic nerve, both optic nerves, the optic chiasm, or in conjunction with hypothalamic glioma. As the glioma grows, it presses and displaces optic nerve tissue and may also result in progressive loss of vision in one or both eyes.

Optic Nerve

A bundle of nerve fiber that connects each eye to the brain and transmits images from the retina to the brain.

Optic Pathway Lesions

The site of damage along the optic pathway determines the type of visual field changes. Optic nerve lesions cause visual disturbances restricted to one eye. Lesions about the chiasm usually affect vision bilaterally. Lesions above or below the chiasm (e.g., a pituitary tumor) destroy nerve fibers supplying the inner (nasal) half of both retinas, resulting in defects in the temporal visual fields (as in bitemporal hemianopia). Lesions in the optic tract, optic radiations, or cerebral cortex produce homonymous hemianopia, with a loss of function in the right or left halves of both visual fields opposite the side affected. This is the most common type of hemianopia and is usually caused by a brain tumor or a cerebrovascular accident.

Glossary P-R


The measurement of the quality of vision throughout the visual field (the total area that can be seen while looking straight ahead) using targets of different sizes and brightness (light levels). The visual field is measured in degrees. VRT STATUS diagnostic measures the central 30 degrees of visual field.

Peripheral Vision

The ability to see or be aware of objects located on the outside edge of one’s field of view; side or lateral vision.

Pituitary Adenoma

A pituitary tumor that frequently produces visual field defects, particularly bitemporal hemianopsia.


The natural deterioration of the eye’s ability to accommodate or to change the shape of its crystalline lens in order to maintain clear vision up close. Onset usually occurs between the ages of 40 and 45 and results in increased dependence on reading glasses.


A wedge-shaped lens that is thicker on one edge than the other. This plastic or glass lens bends light in the direction of its thicker end. Prisms can be used to measure an eye misalignment and / or treat a binocular dysfunction caused by eye coordination problems). A prism is sometimes added to glasses to help improve eyesight due to an eye misalignment or visual field loss.



Decreased or lost vision in one quarter of the visual field in one or both eyes. (Treatable with NovaVision Vision Restoration Therapy).

Radiation Injury to the Brain

Radiation treatment for cancer, leukemia, etc. may produce visual field defects.


The innermost layer of the eye, and the neurological tissue onto which light rays are focused by the lens. The retina contains receptor cells (rods and cones) that send electrical impulses to the brain via the optic nerve when light rays are present.

Glossary S-Z


The white outer layer of the eye.


An island-like area of lost or decreased vision in one or both eyes. Treatable with NovaVision Vision Restoration Therapy.


May occur only once or as epilepsy, a recurrent disorder of cerebral function. Epilepsy is characterized by sudden, brief attacks of altered consciousness, motor activity, and sensory perception, as well as by inappropriate behavior caused by excessive discharge of cerebral neurons. Temporary visual field defects may be caused by seizures but are generally not of a chronic nature. Patients with other indicated primary disorders (stroke, TBI, tumors, etc.) may also experience epilepsy.


The ability to perceive three-dimensional depth, requiring adequate fusion of the images from each eye.


Ischemic stroke occurs among individuals with a history of hypertension, diabetes mellitus, or signs of atherosclerosis, as well as among people with conditions that produce emboli. Several terms are used to define the possible locations of a stroke in the brain:

  • Middle cerebral artery (MCA), frequently produces homononymous hemianopia
  • Internal carotid artery (ICA), may produce hemianopia
  • Anterior cerebral artery (ACA) – less common
  • Posterior cerebral artery (PCA), frequently associated with contralateral homonymous hemianopia
  • Vertebrobasilar – lower brainstem function

Stroke patients may be affected in more than one area.

Subarachnoid Hemorrhage

Sudden bleeding into the subarachnoid space, one of the membranes that cover the brain and spinal cord. Head trauma is the most common cause of subarachnoid hemorrhage, followed by a ruptured intracranial aneurysm.

Traumatic Brain Injury (TBI)

Also known as acquired head injury, closed head injury, and penetrating head injury. Frequently produces visual field defects. Head injury may result in cerebral contusion, acute and chronic subdural hematomas, epidural hematomas, and post-traumatic epilepsy.

Tunnel Vision

A constriction of the visual field, commonly caused by chronic glaucoma, retinal degeneration, a tumor, or a brain disorder that interferes with the fibers connecting the optic nerve to the brain. Only treatable with NovaVision Vision Restoration Therapy when caused by a tumor, brain surgery, or a brain disorder – not when caused by glaucoma, retinal detachment, or retinitis pigmentosa.


The eyes ability to move horizontally. Occurs as either convergence, in which the eyes turn inward, or divergence, in which they turn outward. Accommodative vergence, fusional vergence, proximal vergence, and tonic vergence are types of turns that occur automatically without conscious effort.


A disordered state in which the individual becomes dizzy or feels that he or she is falling, or that his or her surroundings are whirling; common in brain-injured patients.


A complex interaction between the eye and networks of neurons in the brain that process visual stimuli into ideas and images.

Visual Acuity

Sharpness or clearness of eyesight – measured at close, far (distance), and computer/reading distances.
Visual Field

The total area that can be seen while looking straight ahead. Varies among individuals, with the average range lying between 160 and 180 degrees.

Visual Pathway

The route of the nerve impulses from the retina along the optic nerve, and optic nerve radiations to the brain’s sensory cortex located at the base of the skull.

Yoked Prism

Two prisms mounted so that both bases (thick parts) are pointing in the same direction. Yoked prisms create a shift in the position of the visual field by moving incoming images in the same direction before both eyes. Yoked prisms are used to train or compensate for a binocular dysfunction (eye coordination problem) or a visual field loss.