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- tapetum
- Silvery lining behind the retina in some animals active in dim light. Reflects light back through the eye and allows the photoreceptors a second chance to absorb photons.
- tarsal glands
- tarsoconjunctival glands
- Little glands in the eyelids that make a fatty lubricant which they discharge through tiny openings in the edges of the lids. The meibomian glands can become inflamed, a condition termed meibomianitis or meibomitis. Chronic inflammation of the meibomian glands lead to a cyst, also called chalazion, which is a pimple in the margin of the eyelid. The meibomian glands are also known as the meibomian glands, or palpebral glands.
- Tay-Sachs disease (TSD)
- A progressive neurodegenerative disorder affecting babies. The child with TSD usually develops normally for the first few months of life. Then the baby gets an exaggerated startle reaction, and loses head control by 6 to 8 months of age. The infant cannot roll over or sit up, spasticity and rigidity develop, and excessive drooling and convulsions become evident. Blindness and head enlargement set in by the second year. It is fatal by age 5. TSD results from an enzyme deficiency, which in turn allows a fat, named lipid, to be deposited in the brain. It occurs primarily in Ashkenazi Jews of European origin, a group comprising 95 percent of the Jews in the United States.
- tears
- Watery, slightly salty secretion of the lacrimal glands that serve to lubricate the front of
the eye and wash away particles and foreign bodies. Natural tears are composed of three
layers: the outer oily layer, the middle watery layer, and the inner mucus layer.
See Free Eye Tests.
- temple
- Side pieces of an eyeglass frame that hook over or behind the ear to hold the glasses firmly
in place.
See Free Eye Tests.
- temporal
- Eye care terminology referring to the direction leading toward the ear or temple, away
from the nose.
See Free Eye Tests.
- thermokeratoplasty
- Refractive eye surgery procedure that involves use of the Holmium laser to heat and
shrink tissues in the peripheral area of the cornea in order to change the shape of the
cornea to correct farsightedness and/or some cases of astigmatism.
See Refractive Surgery in Eye Care Encyclopedia.
See Free Eye Tests.
- tonometer
- Instrument used by the eye care professional to determine the intraocular or internal
pressure of the eye.
See Free Eye Tests.
- tonometry
- Measurement of intraocular pressure of the eye in millimeters of mercury.
See Free Eye Tests.
- toric
- Contact lenses that contain a cylinder component to correct astigmatism by bearing two
different optical powers at right angles to each other. These lenses may be thicker in one
meridian to enable the lens to maintain proper orientation on the eye.
See Free Eye Tests.
- trachoma
- Severe, chronic, contagious conjunctival eyelid and corneal infection caused by a virus.
Leads to corneal blood vessel formation, corneal clouding, conjunctival and eyelid scarring
and dry eyes. Leading cause of blindness in the world.
See Free Eye Tests.
- trifocals
- Eyeglass or contact lens design that includes three focal areas: usually a reading lens, a
lens for faraway viewing, and a lens for mid-distance viewing.
See Free Eye Tests.
- twenty-twenty vision (20/20)
- Normal visual acuity as gauged by the Snellen Eye Chart. A person with a normal optical
system (20/20 vision) can see standardized symbols on the chart at a distance of 20 feet. A
person with 20/30 vision can see symbols on the chart from 20 feet that a person with
normal vision could see from 30 feet.
See General Eye Examination in Eye Care Encyclopedia.
See Free Eye Tests.
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