accommodation: the tightening of the ciliary muscle which causes the lens to become more convex.
accommodation/convergence relationship: the relationship by which accommodation and convergence stimulate each other and change in proportion to each other as the distance to the viewed object changes.
acquired myopia: myopia which develops in a normal eye as a result of excessive close work.
acuity: see visual acuity.
anterior chamber: the portion of the eye located between the cornea and the lens.
aqueous: the liquid which fills the anterior chamber.
astigmatic: pertaining to astigmatism.
astigmatism: the eye condition in which light rays from a single point are not brought to a single focus.
axial-length myopia: permanent myopia resulting from an overelongation of the eye.
bifocals: glasses having lenses with different powers in the upper and lower portions.
binocular vision: vision using both eyes.
cataract: a clouding of the lens of the eye.
choroid: the middle coat at the rear of the eye, located between the retina and the sclera.
ciliary muscle: the circular muscle which surrounds the lens and controls its shape.
concave lens: a lens which is thicker at the periphery than at the center.
congenital: existing at birth.
convergence: the turning in of the eyes toward the nose.
convex lens: a lens which is thicker at the center than at the periphery.
cornea: the transparent part of the coat of the eye which covers the iris and pupil and admits light.
cylindrical lens: a lens which is shaped like the surface of a cylinder.
diopter: a unit used to express the power of a lens.
emmetropia: the eye condition in which the light rays from distant objects come to a focus at the retina when the accommodation is relaxed.
emmetropic: pertaining to emmetropia.
far point: the limit of clear vision, beyond which the vision is blurred.
farsightedness: see hyperopia.
floaters: odd-shaped spots which appear to float and jump around in the field of vision.
focal length: the distance of the focal point from the surface of a lens.
focal point: the point at which light rays meet after passing through a lens.
focus: to cause light rays to come together at a point.
fogging: using a lens which causes the vision to be blurred.
fovea: the small area of the retina which gives the sharpest vision.
fusion: the condition where the retinal images in both eyes are seen as one image.
genetic: see hereditary.
glaucoma: a disease marked by increased pressure inside the eye and a gradual loss of vision.
hereditary: passed on from parent to offspring.
hypermetropia: see hyperopia.
hyperopia: the eye condition in which the light rays from distant objects would not come to a focus unless projected behind the retina.
hyperopic: pertaining to hyperopia.
intraocular pressure (IOP): the pressure of the fluid inside the eye, usually expressed in millimeters of mercury.
iris: the colored portion of the eye which regulates the size of the pupil.
lens: the part of the eye which changes its shape to focus the eye for different distances.
M.D.: the abbreviation for Doctor of Medicine.
macula: the portion of the retina in which the fovea is located.
minus lens: see concave lens
myope: a myopic person.
myopia: the eye condition in which the light rays from distant objects come to a focus before reaching the retina.
myopic: pertaining to myopia.
Myopter viewer: an optical device which simulates distance vision when used for close work.
nearsightedness: see myopia.
negative accommodation: the active relaxation of the ciliary muscle which causes the lens to become less convex.
O.D.: 1) abbreviation for Doctor of Optometry. 2) the abbreviation for "oculus dexter" which is used on prescriptions to indicate "right eye.
O.S.: the abbreviation for "oculus sinister" which is used on prescriptions to indicate "left eye."
O.U.: the abbreviation for "oculus uterque" which is used on prescriptions to indicate "both eyes."
oculist: see ophthalmologist.
ophthalmologist: a physician who specializes in eye care, including surgery and the treatment of disease.
optician: a person who makes or sells glasses.
optometrist: an eye specialist trained to examine the eyes, detect defects, and prescribe lenses and exercises.
periphery: the outer edge of a lens.
plus lens: see convex lens.
presbyopia: the gradual loss of the power of accommodation with advancing age, making convex lenses necessary for close work.
prismatic lens: a lens which changes the direction but not the focus of the light rays passing through it.
pupil: the opening in the center of the iris which admits light.
pupillary distance: the distance between the pupils of the eyes, usually expressed in millimeters.
reading glasses: glasses with lenses selected for use in close work and not for distance.
refraction: 1) an examination of the refractive status of the eye. 2) the result of an examination, expressed in diopters. 3) the bending of light rays that occurs when they pass from one medium into another.
refractive error: the amount, expressed in diopters, by which the optical properties of the eye differ from emmetropia.
retina: the innermost coat at the rear of the eye which receives the image formed by the cornea and the lens and is connected to the brain by the optic nerve.
sclera: the outermost coat at the rear of the eye.
single-vision lenses: lenses with the same power over the entire surface.
spastic myopia: temporary myopia resulting from a spasm of the ciliary muscle.
spherical lens: a lens which is shaped like the surface of a sphere.
stereopsis: see stereoscopic vision.
stereoscopic vision: the seeing of objects in three dimensions.
suspensory ligament: the structure which supports the lens.
visual acuity: sharpness of vision.
vitreous: the jelly-like substance which fills the vitreous chamber.
vitreous chamber: the portion of the eye located between the lens and the retina.