Eyesight Dictionary

Emmetropia

Normal vision, no correction needed. (See diagram of the eye.)

Esophoria (Eso) (clinical condition)

A tendency of the eyes to want to turn more inward than necessary when an individual is viewing an object at near or at distance, which may cause the individual to experience eyestrain and other symptoms. Symptoms of basic esophoria include: eyestrain, headaches, blurred or double vision, apparent movement of print, and difficulty concentrating on and comprehending reading material. Clinical signs of basic esophoria include: AC/A ratio is normal, equal esophoria at distance and near, and normal near point of convergence. Sometimes esophoria is caused by a refractive error such as hyperopia (farsightedness), and glasses or contacts can correct the problem alone. However, sometimes vision therapy is needed to to help re-train the eyes to function more appropriately. (See "Convergence Excess" and "Divergence Insufficiency")

Esotropia (ET) (clinical condition)

A condition in which an eye is turned either constantly or intermittently inward toward the nose. Esotropia is a type of strabismus. It is caused by a reduction in visual acuity, reduced visual function, high refractive error, traumatic brain injury, oculomotor nerve lesion, or eye muscle injury. Treatment options may include one or more of the following: glasses or contacts, bi-focal lenses, prisms, vision therapy, surgery, or Botulinum Toxin Type A (Oculinum, Botox®) injections. In some cases, esotropia is caused by a refractive error such as hyperopia (farsightedness), and glasses or contacts alone may allow the eyes to straighten. Vision therapy is most appropriate when there are small degrees of misalignment. Surgery, to re-position or shorten the eye muscles, may be required for high degrees of misalignment. If surgery is required, a combination of surgery and vision therapy often yields the best results. For more information, please click here. (See “Strabismus”)

Exophoria (Exo) (clinical condition)

A tendency of the eyes to want to turn more outward than necessary when an individual is viewing an object at near or at distance, which may cause the individual to experience eyestrain and other symptoms. Symptoms of basic exophoria include: eyestrain, headaches, blurred or double vision, apparent movement of print, and difficulty concentrating on and comprehending reading material. Clinical signs of basic exophoria include: normal AC/A ratio, equal exophoria at distance and near, and decreased near point of convergence. Vision therapy is an effective treatment option. (See "Convergence Insufficiency" and "Divergence Excess")

Exophthalmos

Exophthalmos is a bulging of the eye anteriorly out of the orbit. Exophthalmos can be either bilateral (as is often seen in Grave's Disease) or unilateral (as is often seen in an orbital tumor). Measurement of the degree of exophthalmos is performed using an exophthalmometer. Complete or partial dislocation from the orbit is also possible from trauma or swelling of surrounding tissue resulting from trauma.

In the case of Graves Disease, the displacement of the eye is due to abnormal connective tissue deposition in the orbit and extraocular muscles which can be visualized by CT or MRI.

If left untreated, exophthalmos can causes the eye lids to fail to close during sleep leading to corneal damage. The process that is causing the displacement of the eye may also compress the optic nerve or ophthalmic artery leading to blindness.

Exotropia (XT) (clinical condition)

A condition in which an eye is either constantly or intermittently turned outward toward the ear. Exotropia is a type of strabismus. It may also be called divergent strabismus, wandering eye, or wall eye(s). It is caused by a reduction in visual acuity, reduced visual function, high refractive error, traumatic brain injury, oculomotor nerve lesion, or eye muscle injury. Treatment options may include one or more of the following: glasses or contacts, bi-focal lenses, prisms, vision therapy, surgery, or Botulinum Toxin Type A (Oculinum, Botox®) injections. Vision therapy is most appropriate when there are small degrees of misalignment. If surgery is required, a combination of surgery and vision therapy often yields the best results. For more information, please click here. To see the American Optometric Association's guidelines for vision therapy, please click here. (See “Strabismus”)

Extraocular Muscles

The muscles attached to the outside of the eyeball which control eye movement. Each eye has six muscles (lateral rectus, medial rectus, superior oblique, inferior oblique, superior rectus, and inferior rectus) that are coordinated by the brain. For more information and diagram, please click here.

Eye Hand Coordination

The ability of our eyes to guide our hands, also called visual motor integration.

Eye Trac(equipment)

An electronic testing and recording system of eye movements as in reading.

Eye Tracking

The ability of the eyes to smoothly and effortlessly follow a moving target.

Eye diseases:

Dictionary of terms relating to eyesight and vision.