Glossary

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TermDefinition 
 
Scleral LensA contact lens which fits over the cornea as well as the bulbar conjunctiva.View
Seal-OffWhen the entire edge of a contact lens is firmly pressed against the ocular surface preventing tear exchange.View
Semi-Scleral LensSoft contact lens that extends beyond the limbus onto the conjunctiva. View
Silicone AcrylatePolymer used in the manufacturing of button materials for rigid contact lenses.View
Silicone HydrogelSoft contact lens material with high oxygen permeability.View
Simple Astigmatism Ocular astigmatism where one principle meridian is emmetropic and the other is either myopic or hyperopic. See also Astigmatism.View
Simultaneous Multifocal Contact Lenses This design has both the distance and near vision portion of the lens in front of the pupil at the same time. This design requires the users eyes to ignore near objects when viewing distance objects, and to ignore distant object when focusing near. Pupil size is a big factor when considering these lenses.View
Spherical Aberration The inability of a spherical lens to bring all rays of light to a single focal point. See also Aberration. View
Spherical EquivalentThe sum of the spherical power plus half of the cylindrical power. View
Spherical Refractive ErrorWhen the correcting lens power is equal in all meridians.View
Spin CastA contact lens manufacturing process where a liquid polymer is spun into a prescribed shape and then firmed into a soft lens. View
Stabilization TechniquesMethods used to maintain a contact lenses correct orientation when worn by the patient.View
Stabilizing Agents Stabilizing agents are the opposite of catalysts. This is a chemical which tends to inhibit the reaction between two or more other chemicals.View
Steep “K” The meridian of the cornea that has the shorter radius of curvature.View
StriaeWhite, usually vertical, stress lines found in Descemet's membrane and posterior stroma. View
SurfactantsA surfactant molecule contains both a water insoluble component and a water soluble component enabling them to bind to both protein and water. Surfactants serve as cleaners, especially toward proteins, but also serve as wetting agents.View
Terrien’s Marginal DegenerationA slowly progressive, painless peripheral thinning of the corneal stroma. This finding is typically bilateral and predominantly in men.View
Three and nine o’clock stainingCorneal staining parallel to the nasal and temporal limbus. This clinical finding is due to contact lens associated dry eye.View
TopographyA non-invasive medical imaging instrument used for mapping the curvature of the cornea.View
Toric LensA single lens that has two different powers in two meridians perpendicular to each other.View