In hyperopes, when correcting with spectacles, the induced prism tends to be in which direction?

In hyperopes, when correcting with spectacles, the induced prism tends to be in which direction?

• A. BO prism
• B. BI prism
• C. No prism
• D. BU prism

Answer: (A)

Induced prism from spectacles comes from lens decentration relative to the pupil. For hyperopes the corrective plus lenses are often fitted so the pupil ends up looking through the outer (temporal) portion of the lens. When the eye views through that lateral part, the light is shifted in a way that the eye experiences a prism with its base directed outward. In practical terms, this is called base-out prism. No prism would be expected only if the pupil lined up exactly with the lens center, which is uncommon. A base-in prism would occur if the eye looked through the inner (nasal) portion of the lens, and a base-up prism would require vertical decentration or tilt rather than horizontal decentration from hyperopic correction.

Induced prism from spectacles comes from lens decentration relative to the pupil. For hyperopes the corrective plus lenses are often fitted so the pupil ends up looking through the outer (temporal) portion of the lens. When the eye views through that lateral part, the light is shifted in a way that the eye experiences a prism with its base directed outward. In practical terms, this is called base-out prism.

No prism would be expected only if the pupil lined up exactly with the lens center, which is uncommon. A base-in prism would occur if the eye looked through the inner (nasal) portion of the lens, and a base-up prism would require vertical decentration or tilt rather than horizontal decentration from hyperopic correction.