jump

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jump

The displacement of the image of an object occurring when viewing across the borderline between two portions of different power in a bifocal or trifocal lens. The jump is eliminated by placing the optical centres on the dividing line; the lens is then called a no jump bifocal (e.g. a monocentric bifocal with a straight dividing line) (Fig. J1). Syn. image jump; prismatic jump. See monocentric.
Fig. J1 Image jump upward caused by the segment of a bifocal lens, as the direction of gaze is lowered across the dividing lineenlarge picture
Fig. J1 Image jump upward caused by the segment of a bifocal lens, as the direction of gaze is lowered across the dividing line
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
Occasionally we would realize a cow or horse had jumped the rails, and my cowboy-husband would rope them in before the police did.
According to a JR study, the train should not have jumped the rails unless it was moving at 133 kph or faster.
The 74-year-old's first brush with death came in 1962 when a train he was travelling on from Sarajevo to Dubrovnik jumped the rails and plunged into an icy river.
The passenger train's engine and three carriages jumped the rails in the collision near the town yesterday morning.
Meanwhile, Mi-yeong has completely jumped the rails, silently wandering the seashore and copulating like crazy with half the platoon.