A + DBL for a frame is equivalent to which measurement?

Study for the NBEO Physiological Optics Test. Prepare with flashcards and multiple-choice questions, each question has hints and explanations. Ace your exam!

Multiple Choice

A + DBL for a frame is equivalent to which measurement?

Explanation:
Frame PD is the distance between the centers of the two lenses when the frame is worn. The A value is the horizontal width of one lens (eye size), and the DBL is the distance between the inner edges of the two lenses (the bridge). The centers of the lenses sit at half of each lens’s width from the inner edge, so the center-to-center distance is A/2 + DBL + A/2, which simplifies to A + DBL. Therefore, A + DBL for a frame equals the frame PD.

Frame PD is the distance between the centers of the two lenses when the frame is worn. The A value is the horizontal width of one lens (eye size), and the DBL is the distance between the inner edges of the two lenses (the bridge). The centers of the lenses sit at half of each lens’s width from the inner edge, so the center-to-center distance is A/2 + DBL + A/2, which simplifies to A + DBL. Therefore, A + DBL for a frame equals the frame PD.

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