For plus-powered spectacles, prism is oriented in which direction?

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Prepare for the NBEO Physiological Optics Test with flashcards and multiple choice questions, each offering hints and explanations. Equip yourself for your exam!

Multiple Choice

For plus-powered spectacles, prism is oriented in which direction?

Explanation:
Prism orientation is described by where the base, the thicker part of the prism, faces. In plus-powered lenses, the center of the lens is thicker than the edges, so light tends to bend toward the center of the lens. When two plus lenses are worn, any natural prismatic effect from decentration or frame alignment tends to have the bases directed toward the midline between the eyes. That places the prisms in both eyes with their bases facing each other, i.e., base-to-base.

Prism orientation is described by where the base, the thicker part of the prism, faces. In plus-powered lenses, the center of the lens is thicker than the edges, so light tends to bend toward the center of the lens. When two plus lenses are worn, any natural prismatic effect from decentration or frame alignment tends to have the bases directed toward the midline between the eyes. That places the prisms in both eyes with their bases facing each other, i.e., base-to-base.

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