Welch Allyn SureSight Vision Screener - User Manual - Manual (Page 30)

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Appendix
Glossary of Terms
Amblyopia: An uncorrectable marked loss of visual acuity in one eye; “lazy-eye”.
Causes of amblyopia include: refractive errors, strabismus, and cataracts.
Anisometropia: The difference in refractive error between the two eyes, also
known as refractive difference.
Astigmatism: A refractive error due to an uneven curvature of the cornea,
resulting in asymmetrical focus which blurs some of what the person sees. An
astigmatic eye typically has areas of the cornea that are steeper or flatter than
normal, which produces distorted vision.
Cylinder: A measure of the power of astigmatism
False Negative: A test or procedure that indicates the abnormality or disease
being investigated is not present when in fact it is.
False Positive: A test or procedure that indicates the abnormality or disease
being investigated is present when in fact it is not.
Focal Length: The distance at which a lens focuses.
Hyperopia: Far-sightedness; close images are blurry due to the rays of light
converging on the retina short of the focal length at which they would be in focus.
Myopia: Near-sightedness; a condition in which distant images are blurry
resulting from too much focusing power in the lens and cornea. The light rays
focus in front of the retina rather than at the retina.
Sphere: The power of the eye, which determines hyperopia and myopia.
Strabismus: Intermittent or constant misalignment of the eyes; sometimes
referred to as muscle problems.