Glossary

Astigmatism
An error of refraction in which light rays are not focussed sharply on the retina. Astigmatism is due to differences in curvature of the cornea. Astigmatism is believed to be inherited, and can be improved or eliminated by corrective lenses or reshaping of the curvature with the Excimer laser.

Cornea
The clear, transparent front window to the eye which plays a key part in the refraction of light.

Epithelium
The cellular covering of internal and external surfaces of the body, including the eye. It consists of cells joined by small amounts of cementing substances. These cells are removed manually before PRK, and grow back in 3-5 days.

Excimer Laser
Belonging to a family of cool beam ultraviolet rays, the Excimer is the most easily applicable to precise corneal shaping. Functions of this type of laser are controlled by computer software.

Hyperopia
(Farsightedness) A visual defect in which parallel light rays reaching the eye focus behind the retina. Vision is better for distant objects than for near.

LASIK
Laser Assisted In-Situ Keratomileusis Or " Flap and Zap" where a partial thickness of corneal tissue is hinged to get at the corneal tissue to do the laser correction.

Microkeratome
The instrument used to make the corneal flap to do LASIK or " flap & zap"

Myopia
(Nearsightedness) the most common sight disorder, resulting either from an eye that has grown too long, or a cornea with too much curvature. In the myopic eye, objects viewed from a distance appear out of focus, while near objects are seen clearly.

Presbyopia
A condition of the eye which begins around the age of 40. The crystalline lens inside the eye loses flexibility with age, and causes the need for reading glasses.

Photorefractive Keratectomy (PRK)
A surgical procedure performed with an Excimer laser to correct refractive disorders such as myopia, hyperopia, and astigmatism.