Vision Diseases, Disorders & Definitions

# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

S Defintions


Opaque, fibrous, protective outer layer of the eye (white of the eye) that is directly continuous with the cornea in front and with the sheath covering optic nerve behind.

Single Vision:

A lens that has one sphere power and/or one cylindrical power.

Slit lamp:

Microscope used for examining the eye; allows cornea, lens and otherwise clear fluids and membranes to be seen in layer-by-layer detail.

Snellen chart:

Test chart used for assessing visual acuity. Contains rows of letters, numbers, or symbols in standardized graded sizes, with a designated distance at which each row should be legible to a normal eye. Usually tested at a distance of 20 feet.


Eye misalignment caused by extraocular muscle imbalance; one fovea is not directed at the same place in a scene as the other. This is usually corrected through the use of prisms.

Standard Lenses:

Lenses that are made of either tempered glass or CR-39 plastic manomer. Standard lenses are typically not coated or tinted.


Portions of this page are excerpted from Dictionary of Eye Terminology, copyright 1990-2006 by Barbara Cassin and Triad Communications. Reprinted with permission.

Some of the information above is reprinted from the National Eye Institute, National Institutes of Health, and is for educational purposes only. Superior Vision strongly recommends eye exams as the best way to diagnose eye conditions and learn more about potential vision problems.