Ophtalmic glossary

Ability of the eye to change its focus between distant objects and near objects.

Sharpness of central vision. Normal visual acuity is defined as 20/20 vision in relation to the Snellen acuity chart. This is the eye chart used to establish your glasses prescription, with rows of letters that start large at the top and get smaller towards the bottom

Condition of the eyes in which they have unequal refractive power.

Structural defects of the eye in which the light rays from a viewed object do not meet in a single focal point, resulting in blurred images being sent to the brain. An astigmatic cornea is not perfectly rounded like a basketball but has an irregular shape more like the side of a football. Astigmatism is most often combined with myopia or hyperopia.

Simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and parallax-induced depth perception.

Transparent tissue that forms the front part of the eyeball, covering the iris and pupil. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power.

Refers to the degree of astigmatism (uneven roundness) present in the cornea.

Unit of measure of the refractive power of an optical lens (equal to the power of a lens with a focal distance of one meter). A negative diopter value (such as -3D) signifies an eye with myopia and positive diopter value (such as +3D) signifies an eye with hyperopia.

Common term for hyperopia.

Abbreviation for the Food and Drug Administration. It is the United States governmental agency responsible for the evaluation and approval of medical devices.

Also called farsightedness, hyperopia is the inability to see near objects as clearly as distant objects, and the need for accommodation to see distant objects clearly.

An inherited corneal disease. The cornea gradually becomes thinner and less able to maintain its shape against the pressure of the fluids inside the eye. It bulges forward, blurring vision and may eventually require a corneal transplant.

Common term for myopia.

Also called nearsightedness or shortsightedness, the inability to see distant objects as clearly as near objects.

Non-surgical procedure using contact lenses to alter the shape of the cornea to effect a change in the refractive error.

Inability to maintain a clear image (focus) as objects are moved closer. Presbyopia is due to reduced elasticity of the lens with increasing age.

Test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another.

A tool used to see the refractive problems that might be present in the cornea. Corneal topography is used not only for screening all patients before refractive surgery like LASIK but also for fitting contacts.