Glossary

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TermDefinition 
 
AberrationAn unequal refraction or focalization of light rays.View
Accommodative Astigmatism Ocular astigmatism induced by alterations of the curvatures of the crystalline lens. See also Astigmatism.View
Against-The-Rule AstigmatismThe flattest (longest) radius of corneal curvature lies vertically and the steepest (shortest) curve of the cornea is horizontal. This form of astigmatism has its greatest refractive power in the horizontal meridian. See also Astigmatism. View
Alternating Multifocal Contact LensesThis design has distinct zones in the lens for distance and near vision. When the user looks straight ahead they are using the distance portion of the lens. When looking down, correct lid interaction allows for near vision through the inferior portion of the lens. The near segment can be designed in a half-moon, crescent, or annular shape. Stabilization techniques use prism ballast or truncation. View
Annular Multifocal Contact LensesSee also Concentric Multifocal Contact Lenses. View
Apical BearingA resulting fluorescein pattern where the posterior lens curvature lightly touches the corneal apex .View
Apical ClearanceA resulting fluorescein pattern where the posterior lens curvature does not touch the corneal apex .View
Apical PoolingSee also Apical Clearance.View
Apical TouchA resulting fluorescein pattern where the posterior lens curvature rests on the corneal apex .View
Aspheric LensA lens design where one or both surfaces of the lens are non-spherical. An aspherical surface is designed to reduce various forms of optical aberrations. See also Aberration. View
Aspheric Multifocal Contact LensesSee also Simultaneous Multifocal Contact Lenses.View
AstigmatismA vision disorder that occurs when the cornea of the eye is uneven in shape. Astigmatism may also result from the irregular way the natural crystalline lens refracts light. Both causes result in light rays that focus at more than one point on the retina. View
Axial Edge LiftSee also Edge Lift.View
Back Optic Zone Diameter (BOZD)Diameter of the central back optic zone measured by the surrounding junction.View
Back Optic Zone Radius (BOZR)The radius of curvature of the back optic zone; previously called the back central optic radius (BCOR) View
Back Peripheral Radius (BPR)The radius of curvature of the peripheral zone surrounding the central optic zone.View
Back Peripheral Zone Diameter (BPZD)The diameter of the back region surrounding the central optic zone.View
Back Surface ToricLens design where part or the entire posterior surface of the lens is of a toric construction. See also Toric Lens. View
Bandage Contact LensA soft contact lens worn to protect or treat a diseased or injured cornea. View
Bi-AsphericLens design where the posterior surface of the lens consists of two different aspheric curves. See also Aspheric Lens. View