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Glossary of Terms: Vision, Visual Health

AMBLYOPIA ("lazy eye"): a visual defect that affects approximately 2 or 3 out of every 100 children in the United States. Amblyopia involves lowered visual acuity (clarity of sight) in one eye which can not be corrected by glasses or contact lenses. The result is often a loss of stereoscopic vision (3D) and depth perception. Vision therapy can improve this condition. Early detection and treatment offer the best outcome.


For many years, it was thought that amblyopia (lazy eye) was only amenable to treatment up to the age of seven or eight years. Scientific research by the National Eye Institute, National Institutes of Health, Department of Health and Human Services has now proven that effective treatment can take place up to the age of 17. Scientific research on treatment after the age of 17 has not yet been done. Nevertheless, behavioral/developmental optometrists report decades of successful treatment results with adult amblyopia patients. The length of the treatment period does increase dramatically the longer the condition has existed prior to treatment, so early detection and treatment are still preferred.


There are many reasons that early childhood eye examinations and proper treatment are essential. Research has also demonstrated that patients with amblyopia are more likely to sustain injuries resulting in the loss of their good eye than individuals with two good eyes.

See more in-depth information at What is Amblyopia (Lazy Eye)?


See Find a Doctor for a free referral to an eye doctor who offers comprehensive eye examinations to children of all ages, including infants.


People often confuse amblyopia (lazy eye) with strabismus (crossed eyes, eyes that wander, turn or deviate). These are two different but sometimes interrelated visual problems. See Strabismus below or a comprehensive web site at What is Strabismus?


BEHAVIORAL OPTOMETRIST: See Developmental Optometrist below.

BINOCULAR: Of or involving both eyes at once.


BINOCULAR VISION: vision as a result of both eyes working as a team; when both eyes work together smoothly, accurately, equally and simultaneously.


BINOCULAR DEPTH PERCEPTION: a result of successful eye teaming and stereoscopic vision; the ability to visually perceive three dimensional space; the ability to visually judge relative distances between objects; a visual-motor skill that aids accurate movement in three-dimensional space.


BINOCULAR VISION IMPAIRMENT: A visual defect in which the two eyes fail to work together as a coordinated team resulting in a partial or total loss of binocular depth perception and stereoscopic vision. At least 12% of the population has some type of binocular vision impairment. Amblyopia and strabismus are the most commonly known types of binocular vision impairment. To find out more, see What is Convergence Insufficiency?, What is Amblyopia (Lazy Eye)?, What is Strabismus?, and/or What is Binocular Vision Impairment?


CONVERGENCE INSUFFICIENCY: is a common near vision problem that interferes with the child's ability to see, read, learn, and work at near (close distances). An eye teaming problem in which the eyes have a strong tendency to drift outward or away from the target when reading or doing close work. When the eyes drift, the child might have double vision. The condition can manifest or worsen in the later school years as near work, homework, and reading demands increase significantly.

Convergence insufficiency disorder often goes undetected and untreated in children because testing for this common vision disorder is typically not included in (1) pediatrician's eye tests; (2) school eye screenings; or (3) the basic 20/20 eye exam. Please note that a child can pass the 20/20 eye test and still have convergence insufficiency. The National Eye Institute and Mayo Clinic recently proved that in-office vision therapy is the best treatment for convergence insufficiency in children. For comprehensive information on symptoms, complications and treatment, go to What is Convergence Insufficiency?

DEVELOPMENTAL OPTOMETRIST:(also, known as Behavioral Optometrist or Pediatric Optometrist) a doctor of optometry who belongs to an international branch of optometry which specializes in the practice of In-office Vision Therapy. The term "behavioral" came into use because these optometrists will consider how environmental, nutritional and/or behavioral factors affect visual health and function. The practice focus or methodology of behavioral optometrists has absolutely nothing to do with Behaviorism (B. F. Skinner). See the Directory for a free referral to behavioral, developmental or pediatric optometrists.

DIPLOPIA OR DOUBLE VISION: See What is Double Vision?


DYSLEXIA: (dyslexic). Margaret S. Livingstone, Ph.D., Professor of Neurobiology, Dpt. of Neurobiology, Harvard Medical School defined dyslexia as follows: "Developmental dyslexia is the selective impairment of reading skills despite normal intelligence, sensory acuity, and instruction. It is important to note that Dr. Margaret Livingstone defines dyslexia as "impairment of reading skills DESPITE NORMAL...SENSORY ACUITY." Normal vision and normal hearing are essential parts of normal sensory acuity, so it is critical to rule out any problems with vision or hearing when considering the diagnosis and/or treatment of dyslexia. Notably, normal vision is NOT defined as 20/20 acuity alone. A 20/20 eye test only tests how the person sees at the distance of 20 feet. A person can pass a 20/20 test and still have serious vision problems. Likewise, the standard hearing test only looks for hearing loss, but does not test for other auditory processing abnormalities.

Dr. Livingstone's research on developmental dyslexia also showed that "Visual abnormalities were reported to be found in more than 75% of the reading-disabled children tested." This statement was made about reading-disabled children, not dyslexic children. Therefore, it is imperative that testing for possible dyslexia be multi-disciplinary and include thorough testing of the child's sensory function and integration. See an article on Vision, Learning and Dyslexia by the American Optometric Association.



OPHTHALMOLOGIST OR PEDIATRIC OPHTHALMOLOGIST: A doctor of medicine (M.D.) specializing in surgery and diseases of the eye. To learn more about the differences between the practices of pediatric ophthalmologists and pediatric optometrists, visit our web page on Choosing an Eye Doctor and What is the difference between an optometrist and an ophthalmologist?.


ORTHOPTIC THERAPY: a small part or limited form of Vision Therapy which trains convergence (eye teaming) skills and visual acuity only. A non-surgical or post-surgical treatment, it is typically home-based. Mayo Clinic and the National Eye Institute have proven that in-office Vision Therapy is more effective in the treatment of a convergence disorder. Orthoptics do not address sensory integration or visual processing issues. Orthoptics first became popular in Europe in the 1900s. David Wells, M.D., an ophthalmologist at Boston University, is credited with introducing orthoptics to the U.S. in 1912. Currently, orthoptics is practiced by very few ophthalmologists and/or orthoptists in the United States. Opthalmologists are typically surgeons and are usually no longer offering this non-surgical treatment.


STEREOPSIS: (stereopsis or stereoscopic vision) a byproduct of good binocular vision; vision wherein the separate images from two eyes are successfully combined into one three-dimensional image in the brain. To learn more, visit an easy-to-understand, illustrated page on Stereo Vision!


STRABISMUS OR CROSSED EYES: ("crossed eye", "wall eye", "wandering eye", strabismus, esotropia, exotropia, hyperphoria): affects approximately 4 out of every 100 children in the United States. It is a visual defect in which the two eyes point in different directions. One eye may turn either in, out, up, or down while the other eye aims straight ahead. Due to this condition, both eyes do not always aim simultaneously at the same object. This results in a partial or total loss of stereo vision and binocular depth perception. The eye turns may be visible at all times or may come and go. In some cases, the eye misalignments are not obvious to the untrained observer.


A consultation with an optometrist who offers supervised in-office Vision Therapy is recommended with this binocular vision condition. Visit the most comprehensive site on What is Strabismus? on the internet! Also visit another doctor's page on strabismus on this site. See the Referral Directory: Find a Pediatric Eye Doctor for a free referral to an eye doctor who specializes in the treatment of crossed eyes.


VISION: The act of perceiving visual information with the eyes, mind, and body.


VISION & ATTENTION DEFICIT DISORDER: (also known as Attention Deficit Hyperactivity Disorder, Attention Deficit Hyperactive Disorder, ADD-ADHD, AD/HD, ADD/ADHD). Read about Vision and ADD-ADHD - Attention Deficit Disorder?


VISION THERAPY: (also known as vision training, visual therapy, visual training): supervised therapy involving procedures (eye exercises) which are aimed at improving visual skills such as eye teaming, binocular coordination and depth perception, focusing, acuity (clarity of sight), and "hand-eye" or "vision-body" coordination. Vision therapy can involve a variety of procedures to correct neurophysiological or neurosensory visual dysfunctions.


Some vendors of self-help eye exercise kits have taken to advertising under the term "Vision Therapy." This is misleading. Vision Therapy is practiced by optometrists and includes evaluation, supervision, and the use of medically regulated devices. See comprehensive information at What is Vision Therapy?
To locate an eye doctor who provides comprehensive pediatric vision examinations and treatment, including Vision Therapy, request a referral through our Referral Directory: Find a Pediatric Eye Doctor.
All other images and text: copyright © 1996- by Rachel Cooper. All rights reserved.
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