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Eye Conditions Glossary
Ametropia
Refractive error that prevents the eye from focusing the image of distant objects on the retina; includes hyperopia, myopia and astigmatism.
Astigmatism
Uneven curvature of the cornea. Corrected with cylindrical lenses (denoted by plus or minus power and axis).
Farsightedness
see Hyperopia
Floaters
Small particles in the vitreous which may be of embryonic or pathological origin (e.g. in retinal detachment, vitreous detachment). The patient sees spots especially against a bright background which float as the eye moves. Floaters are common in normal older eyes.
Hyperopia (farsightedness)
A refractive error in which the eyeball is too short or the lens system of the eye is too weak causing light rays to focus behind the retina. Can be corrected with convex or plus (+) lenses.
Legal Blindness
In the U.S., this is a term defined in the Social Security Act (section 216(i)1) as central visual acuity of 20/200* or less in the better eye with the use of a correcting lens, or a limitation in the field of vision such that the widest diameter of the visual field subtends an angle no greater than 20 degrees.
Myopia (nearsightedness)
A refractive error in which the eyeball is too long or the lens system of the eye is too powerful causing light rays to focus in front of the retina. Can be corrected with concave or minus (-) lenses
Nearsightedness
see Myopia
Presbyopia
Reduced ability to focus that usually occurs in middle age due to the hardening and inelasticity of the crystalline lens. It is corrected with plus lenses.
Refractive error
A defect in the eye's ability to bring light rays to focus on the retina. Refractive errors can be corrected to normal vision.
* This means that what a person with normal vision can see at 200 feet, a legally blind person can see at 20 feet.