Page 91 - The Book Pi in eye

Pi in eye

Corneal topographer: An instrument that creates a three-
dimensional map of the cornea, using computerized analysis.

Crystalline lens: See lens.
Cylinder: One of three measures in an eyeglass prescription. It
indicates whether astigmatism is present, and to what degree.

Dilate: To become larger, as when the pupil enlarges in very dim light
conditions.

Diopter: A measurement of how strong a lens is. One diopter lens is
one that will bring light from very far to focus at one meter. Thicker
lenses have a higher number of diopters. In eye care, it is used to
measure your refractive error, or what eyeglass lens is needed to
correct your vision. Hyperopia is measured in terms of positive
diopters whereas myopia in terms of negative diopters.

Dry eye: A condition characterized by corneal dryness due to
inadequate tear production.

Endothelium: The innermost layer of the cornea, a single cell thick,
that helps regulate the cornea's hydration.

Enhancement procedure: A secondary treatment with the excimer
laser to fine-tune one's visual acuity after the initial Prelex procedure.
Enhancements take place after vision has stabilized, usually three to
six months after Prelex.

Epi-LASIK: A variant of PRK in which the epithelium (the clear skin
that covers the eye) is peeled off by an automated machine called an
epikeratome.

Epithelium: The thin, protective outermost surface of the cornea. It
is made up of the same kind of cells as the skin. It also grows rapidly
and continually regenerates.

Excimer laser: The type of laser used in refractive surgery to remove
corneal tissue. It emits highly precise pulses of ultraviolet light to

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