Dictionary of terms relating to
eyesight and vision

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To block out light. An eye can be completely or partially blocked. This procedure is used to promote the use of one eye or both eyes. This therapy procedure may be used for people with amblyopia, strabismus, or closed head trauma. It may also be used in a vision therapy program for someone with amblyopia, eye focusing (accommodation) disorder, or poor eye tracking (oculomotor) skill. An eye patch, black contact, or another device may be used to block out light from an eye. (See "Direct Occlusion" and "Inverse Occlusion")

Ocular Motility

Pertaining to binocular alignment and eye muscle movement. (See "Binocularity", "Strabismus")

Ocular Motor (OM)

General eye movement ability, which include pursuits (to visually track and/or follow moving objects) and saccades (to direct and coordinate eye movement as the eye quickly and voluntarily shift from one target to another).

Ocular Motor Dysfunction

Poor eye movement skills. Vision therapy is an effective treatment option. To see the American Optometric Association's guidelines for vision therapy, please click here. (See "Pursuits Dysfunction" and "Saccades Dysfunction")

Oculomotor Skills

The ability to quickly and accurately move our eyes. These are sensory motor skills that allow us to move our eyes so we can fixate on objects (fixation), move our eyes smoothly from point to point as in reading (saccades), and to track a moving object (pursuits). (See "Fixation", "Pursuits" and "Saccades")

Oculus Dexter (OD)

Right eye.

Oculus Sinister (OS)

Left eye.

Oculus Uterque (OU)

Both eyes.


A physician (doctor of medicine (M.D.) or doctor of osteopathy (D.O.) who specializes in the comprehensive care of the eyes and visual system in the prevention of eye disease and injury. The ophthalmologist has completed four or more years of college premedical education, four or more years of medical school, one year of internship, and three or more years of specialized medical and surgical training and experience in eye care. The ophthalmologist is a physician who is qualified by lengthy medical education, training and experience to diagnose, treat and manage all eye and visual system problems, and is licensed by a state regulatory board to practice medicine and surgery. The ophthalmologist is the medically trained specialist who can deliver total eye care: primary, secondary and tertiary care services (i.e., vision services, contact lenses, eye examinations, medical eye care and surgical eye care), and diagnose general diseases of the body. An ophthalmologist is not trained to provide vision therapy.


A device used to illuminate the inside of the eye and enlarge the image for examining the retina, optic nerve entrance, arteries, and veins.

Optic Nerve

Is a bundle of nerve fiber that connects each eye to the brain and transmits images from the retina to the brain. (See diagram of the eye)

Optic disc:

The circular area in the back of the inside of the eye where the optic nerve connects to the retina. Also called the optic nerve head.


iIs a professional in the field of designing, finishing, fitting and dispensing of eyeglasses and contact lenses, based on an eye doctor's prescription. The optician may also dispense colored and specialty lenses for particular needs as well as low-vision aids and artificial eyes.

Optometric Vision Therapy (VT)

As defined by the American Optometric Association: Optometric vision therapy is a treatment plan used to correct or improve specific dysfunctions of the vision system. It includes, but is not limited to, the treatment of strabismus (turned eye), other dysfunctions of binocularity (eye teaming), amblyopia (lazy eye), accommodation (eye focusing), ocular motor function (general eye movement ability), and visual-perception-motor abilities.

Optometric vision therapy is based upon a medically necessary plan of treatment which is designed to improve specific vision dysfunctions determined by standardized diagnostic criteria. Treatment plans encompass lenses, prisms, occlusion (eye patching), and other appropriate materials, modalities, and equipment. (Vision therapy can also be called visual or vision training, orthoptics, eye training, or eye exercises.)

Please note that the definition above describes Optometric Vision Therapy, which has been clinically shown to improve certain eye disorders, which are described above. However Optometric Vision Therapy is NOT the same as the Bates Method, vision therapy using Bates, integrated vision therapy, or natural eye exercises. These holistic programs use some form of eye exercises associated with relaxation techniques, which claim to improve nearsightedness, farsightedness, astigmatism, decreasing vision with age, and other disorders. There is virtually no statistical studies/results indicating the success of these methods.


A health care professional who is state licensed to provide primary eye care service. These services include comprehensive eye health and vision examinations; diagnosis and treatment of eye disease and vision disorders; the detection of general health problems; the prescribing of glasses, contact lenses, low vision rehabilitation, vision therapy, and medications; the performing of certain surgical procedures; and the counseling of patients regarding their surgical alternatives and vision needs as related to their occupations, avocations and lifestyle. The optometrist has completed pre-professional undergraduate education in a college or university and four years of professional education at a college of optometry, leading to the doctor of optometry (O.D.) degree. Some optometrists complete a residency.

Organic Amblyopia

Gradual or sudden loss of central vision (partial loss) affecting visual acuity with no treatment options.

Types of organic (irreversible) amblyopia:

Nutritional amblyopia - vision loss caused by low levels of vitamin B12 due to poor nutrition and poor absorption associated with drinking alcohol.
tobacco-alcohol amblyopia- clinical evidence exists that a nutritional deficiency is the underlying cause of this vision loss; however, many still believe that the toxic effects of alcohol and/or tobacco are contributing factors.
toxic amblyopia- caused by exposure to toxins such as ethambutol, methyl alcohol (moonshine), ethylene glycol (antifreeze), cyanide, lead, and carbon monoxide.

Orthophoria (ortho)

The absence of either esophoria or exophoria. The eyes do not have a tendency to want to turn more inward than necessary or want to turn more outward than necessary when pointed on an object.


The science of correcting defects in binocular vision. The technique of eye exercises to correct strabismus (esotropia or exotropia), convergence insufficiency (exophoria), or convergence excess (esophoria), amblyopia, and ocular motility disorders. Orthoptics was pioneered by French ophthalmologist Javal in the mid to late 1800's. Today ophthalmologists use specialty-trained healthcare professionals called orthoptists to evaluate patients and treat them with orthoptics. In America, the non-surgical technique of orthoptics is less commonly used by ophthalmologists compared to other countries. Orthoptics is a limited form of optometric vision therapy.