Glossary
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E-value
Conventional contact lenses typically include an aspheric progressive multifocal zone that is formed by rotating a conic section about a central axis. As used herein, the term "conic section" refers to a curve that results from intersecting a cone with a plane at any angle. A conic section may be mathematically defined in terms of "eccentricity", which is the variation in the shape of an ellipse and is numerically always less than one.
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Eccentricity
Term referring to the angular distance from the centre of the visual field or from the foveola of the retina
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Edema
An abnormal excess accumulation of fluid in a tissue.
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Edge lift
Deviation of the posterior surface of a contact lens from a sphere at a given diameter. This is produced by either the peripheral curve(s) or the edging process. Edge lift provides peripheral clearance of a rigid contact lens, which is assessed by fluorescein pattern. If the edge lift is specified axially (as an extension of the back central optic zone, measured parallel to the axis of symmetry) it is referred to as axial edge lift. If specified radially as an extension along the back optic zone radius it is referred to as radial edge lift.
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Emmetropia
The scientific term for normal vision. When the cornea and lens of the eye focus an image directly on the retina, clear vision is the result.
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Endothelium
The innermost corneal layer of flat, hexagonal cells which function to pump fluid out of the cornea.
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Enhancing tint
A transparent tint on a contact lens which blends with the underlying iris color to achieve a new, enhanced iris color effect.
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Enzymatic cleaner
A cleaner that will decompose or digest protein, muco-protein, or lipoprotein deposits on a contact lens.
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Equivalent oxygen percentage
A lens that is impermeable to oxygen is said to have an EOP of zero; a lens completely permeable to oxygen would have an EOP of 21 (the same as the percentage of oxygen in the atmosphere). The EOP of a contact lens falls between zero and 21, depending upon its material
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Extended wear lens
Worn without removal for sleeping. Most extended wear lenses are worn continuously for a week; several brands are approved for 30-day wear.
