Refractive error types, lens power calculations, and clinical optics concepts tested on the NBEO.
39 cards · basic cards · AI-written, checked twice. Edit anything.
- What is emmetropia?
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The refractive state in which parallel light rays focus exactly on the retina with accommodation relaxed.- What is myopia?
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A refractive error in which parallel light rays focus in front of the retina.- What is hyperopia?
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A refractive error in which parallel light rays focus behind the retina.- What is astigmatism?
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A refractive error in which unequal curvature between meridians causes light to focus at two separate points instead of one.- What is presbyopia?
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The age-related loss of accommodative amplitude caused by progressive hardening and reduced elasticity of the crystalline lens.- What is a diopter?
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A unit of lens (or vergence) power equal to the reciprocal of the focal length measured in meters.- Lens power in diopters equals ____.
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1 divided by the focal length in meters- The thin lens vergence formula is ____, where U is object vergence, D is lens power, and V is image vergence.
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U + D = V- How does increasing vertex distance affect the effective power of a plus (convex) lens?
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It increases the effective plus power at the eye.- How does increasing vertex distance affect the effective power of a minus (concave) lens?
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It decreases the effective minus power at the eye.- Prentice's rule states that induced prism in prism diopters equals ____.
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the decentration in centimeters multiplied by the lens power in diopters- What is the base curve of a spectacle or contact lens?
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The curvature of a reference surface of the lens, commonly the front surface for spectacles, used to define the lens form.- Spherical equivalent equals ____.
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the sphere power plus half the cylinder power- What is with-the-rule astigmatism?
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Astigmatism in which the steepest corneal meridian is near 90 degrees (vertical).- What is against-the-rule astigmatism?
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Astigmatism in which the steepest corneal meridian is near 180 degrees (horizontal).
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