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?
- 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?
- The amount of correction needed for myopia or hyperopia, expressed in diopters.
- What does the cylinder (C) value represent in a prescription?
- The amount of correction needed for astigmatism, expressed in diopters.
- What is the axis in a prescription?
- The meridian angle (0 to 180 degrees) at which cylindrical power is applied to correct astigmatism.
- What is a prism in ophthalmic lenses?
- A correction that shifts the line of sight to compensate for eye muscle imbalances or strabismus.
- What does ADD power mean?
- 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?
- 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?
- Pupillary distance, the distance in millimeters between the centers of the pupils of both eyes.
- What is bridge width?
- The horizontal distance in millimeters between the inner edges of the two lenses where they meet at the nose.
- What is temple length?
- The length in millimeters of the arm of the frame that extends from the hinge to the bend at the ear.
- What is DBL?
- 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?
- 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?
- 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?
- Two perpendicular reference lines on a lens marking the optical center, one horizontal and one vertical.
- What is the optical center of a lens?
- The point on a lens where no prismatic effect occurs, located where the fitting cross intersects.