Thyroid Eye Disease Glossary

This following is general information about thyroid eye disease terms.

To learn more about thyroid eye disease and state-of-the-art, minimally invasive care at Mass. Eye and Ear, visit the Center for Thyroid Eye Disease and Orbital Surgery. This center includes a multidisciplinary team of physicians with expertise in the full spectrum of thyroid eye disease symptoms.

CAT Scan

Also known as a CT scan, this kind of imaging is similar to an X-ray, but produces three-dimensional information about the eye socket and surrounding structures.


Transparent tissue that forms the front part of the eyeball and covers the iris and pupil, providing most of the eye’s optical power. Eye dryness generally affects the cornea.


A physician who specializes in the study and treatment of hormonal conditions, including thyroid disease.


A normal level of thyroid hormone.


Protrusion (“bulging”) of the eye, also known as proptosis.

Extraocular muscle

One of six muscles originating within the eye socket that move each eye. If enlarged due to thyroid eye disease, these muscles may function abnormally, causing double vision.

Eyelid retraction

Abnormally high position of the eyelid, causing the white of the eye (sclera) to become visible, producing a wide-eyed “stare”or look of “surprise.”


A chemical released by a cell or a gland in one part of the body that functions as a messenger that affect cells in other parts of the body. Thyroid hormones are among many types of hormones in the body.


An abnormally low thyroid hormone level.


Typically blue, brown or green, the part of the eye responsible for “eye color”.

MRI scan

This kind of imaging produces three-dimensional information. It differs from a CT scan, and your doctor may choose to order one or the other.

Ophthalmic plastic surgeon

An ophthalmologist who specializes in surgery of the eyelids and eye socket.


A physician who specializes in the medical and surgical diagnosis and treatment of eye diseases and disorders.

Optic nerve

The nerve that travels through the eye socket transmitting all vision information from the eye to the brain. The optic nerve can be affected by thyroid eye disease.


The eye socket. Composed of the portion of the skull that holds the eye, the orbit houses the eyeball and the muscles that move the eye, fat, blood vessels, and nerves.


A physician who specializes in medical and surgical diagnosis and treatment of head and neck disorders, particularly diseases of the ears, nose, sinuses, and throat.


Protrusion (“bulging”) of the eye, also known as exophthalmos.


The black, circular opening in the center of the iris. Its size determines the amount of light that enters the eye.


The outer, white layer of the eye that along with the cornea forms the external, protective coat of the eye.


Misalignment of the eye, which may occur with thyroid eye disease.

Thyroid gland

Located just below the “Adam’s apple” in the neck, this endocrine gland produces hormones (chemicals) that control the metabolism rate.