Lens power terminology, frame fitting measurements, and prescription reading concepts tested on optician certification exams.
36 cards · basic cards · AI-written, checked twice. Edit anything.
- What is a diopter?
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A unit of measurement for the optical power of a lens, equal to the reciprocal of the focal length in meters.- What does the sphere (S) value represent in a prescription?
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The amount of correction needed for myopia or hyperopia, expressed in diopters.- What does the cylinder (C) value represent in a prescription?
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The amount of correction needed for astigmatism, expressed in diopters.- What is the axis in a prescription?
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The meridian angle (0 to 180 degrees) at which cylindrical power is applied to correct astigmatism.- What is a prism in ophthalmic lenses?
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A correction that shifts the line of sight to compensate for eye muscle imbalances or strabismus.- What does ADD power mean?
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The additional magnifying power added to the lower portion of a multifocal lens for near vision correction.- What is the base curve of a lens?
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The curvature of the front surface of a lens, measured in diopters, that determines the overall lens shape and fit.- What is PD in eyeglasses fitting?
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Pupillary distance, the distance in millimeters between the centers of the pupils of both eyes.- What is bridge width?
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The horizontal distance in millimeters between the inner edges of the two lenses where they meet at the nose.- What is temple length?
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The length in millimeters of the arm of the frame that extends from the hinge to the bend at the ear.- What is DBL?
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Distance between lenses, measured in millimeters from the inner edge of one lens to the inner edge of the other lens.- What is pantoscopic tilt?
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The angle at which eyeglass frames tilt downward at the bottom, typically 8 to 12 degrees, for optimal viewing and comfort.- What does segment height refer to?
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The vertical distance in millimeters from the bottom of the lens to the top of the bifocal or progressive segment line.- What is the fitting cross?
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Two perpendicular reference lines on a lens marking the optical center, one horizontal and one vertical.- What is the optical center of a lens?
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The point on a lens where no prismatic effect occurs, located where the fitting cross intersects.
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