Laser eye surgery glossary
T
Twenty twenty vision (20/20 vision)
Normal visual acuity. Upper number is the standard distance (20 feet) between an eye being tested and the eye chart; lower number indicates that a tested eye can see the same small standard-sized letters or symbols as a normal eye at 20 feet. This is the American measurement; the UK version is 6/6.
Tear film
A very thin film of water and other chemicals riding on top of the epithelium that lubricates the front of the eye.
Tissue sparing treatment
Laser eye surgery treatments involve the removal of a small quantity of tissue from the front surface of the eye (the cornea). This will slightly alter the curvature of the cornea, thereby improving your vision. The higher the prescription then, the more tissue needs to be removed. Unfortunately this means that some patients are unable to have laser eye surgery, as it would leave them with a cornea thickness below the safety level. The Bausch and Lomb Zyoptix Tissue-Sparing system has been developed with these patients in mind because it is efficient in minimising the amount of corneal tissue to be removed in order to produce the desired prescription change. Tissue-sparing can remove up to 25% less tissue than standard laser eye surgery treatment. Instead of merely treating the prescription, the laser is guided in its treatment by the actual structure of the eye using the information collated from the scans taken at the initial consultation. This means that no two treatments are the same as each one takes into account the individual differences between each person's eyes.
Tonometer
Equipment used to test the internal fluid pressure inside the eye (IOP). A puff Ionument is an instrument can be used without touching the eye by blowing a small puff of air into the eye. Further reading
Topography
Mapping a surface of the eye used to determine the corneal profile and it's suitability for laser eye surgery. Further reading
Trefoil
A type of higher order aberration. See Aberrations.
