Glossary

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TermDefinition 
 
Corneal StainingThe uptake of fluorescein dye by the irregularities in the corneal or conjunctival epithelium.View
Cylindrical Refractive ErrorWhen the correcting power is located in one specific meridian.View
Daily WearA contact lens designed to be removed before sleeping. View
Dimple veil stainingCorneal staining caused by trapped air bubbles under a poorly fitting rigid gas permeable contact lens.View
DimplingAir bubbles that develop beneath a contact lens that cause small indentations in the corneal epithelium. View
Dioptric Aberration See also Spherical Aberration. View
Direct Astigmatism See also With-The-Rule Astigmatism.View
Disinfecting Agents A substance that is applied to non-living objects in order to destroy microorganisms. View
Disposable LensesSoft contact lenses designed for daily, weekly or monthly replacement.View
DkA measure of oxygen permeability where the permeability is a product of diffusion (D) and solubility (k). View
Dk/tA measure of oxygen transmissibility, where the permeability - a product of diffusion (D) and solubility (k) - is divided by the thickness (t) of the contact lens material used.View
Double Reverse Geometry LensA lens where more than one intermediate curve is steeper than the central optic zone. View
EBMDSee also Epithelial Basement Membrane Dystrophy.View
Edge ClearanceThe relationship between the edge of the lens and the corneal surface as estimated by a fluorescein pattern.View
Edge LiftThe distance from the edge of the contact lens to the imaginary line that would be created by extending the back central optic zone. This relationship is defined as axial edge lift or radial edge lift. Edge lift is a lens design, not a clinical measurement. View
Edge StandoffSee also Edge Clearance. View
EnzymesEnzymes are catalysts that work by lowering the activation energy of a reaction.View
Epithelial Basement Membrane Dystrophy (EBMD)Clinical signs of bilateral epithelial microcysts and whirling superficial defects, such as corneal ridges and opacities. These findings are due to an inadequate corneal basement membrane. View
Extended WearThe use of contact lenses without removal. These designs allow for longer wearing periods of up to 30 consecutive nights.View
FenestrationA hole drilled into a contact lens. This hole assists with oxygen permeability, adhesion and dispersion of air bubbles or dimples. See also Dimpling.View