prism 1,2a,2b Flashcards
(11 cards)
How do prisms affect light passing through them?
Prisms bend light toward the base, causing image displacement. The amount of deviation is proportional to the prism’s power and the distance from the optical center.
What does the base direction of a prism indicate?
The base direction refers to the direction in which the thicker part of the prism is oriented. It determines the direction in which the image will be displaced (e.g., base up, base down, base in, base out).
How are prisms used to correct strabismus?
Prisms are used in strabismus to align the eyes by shifting the image towards the base direction, thereby improving binocular vision and helping the patient align both eyes on the same target.
What are Fresnel prisms and how are they used?
Fresnel prisms are made from polyvinyl chloride (PVC) and are used to temporarily correct prismatic errors. They are lighter than traditional prisms and are commonly used in progressive lenses or for short-term vision adjustments.
How are prisms used in anisometropia?
In anisometropia, prisms are used to compensate for differential prismatic effects between the two eyes due to differences in refractive power. Prisms help to equalize the image size and position in both eyes.
What is decentration in optometry?
Decentration refers to the process of shifting the optical center of a lens from the geometrical center of the lens to the desired position, which can induce a prismatic effect.
How does decentration affect the prismatic power of a lens?
Decreasing the distance from the optical center to the point of interest increases the prismatic effect. The further the optical center is from the pupil, the stronger the prism effect, as calculated using Prentice’s Rule.
What happens when a lens is shifted away from the optical center?
Shifting the lens away from the optical center causes a prismatic effect, where the light passing through the lens is deviated towards the base direction. This can cause diplopia or double vision if the misalignment is not compensated for.
How are prisms used in combination with cylinder lenses?
Prisms can be combined with cylindrical lenses to correct both astigmatism and binocular vision issues simultaneously. The prism helps align the image, while the cylinder corrects for the meridian-specific refractive error.
How do prisms help in the treatment of binocular vision disorders like heterophoria?
A: Prisms help compensate for muscle imbalances in the eyes by shifting the image towards the base direction, aiding in the alignment of both eyes and improving single binocular vision.
How does binocular vision benefit from prism correction in patients with convergence insufficiency?
In convergence insufficiency, prisms are used to shift the image towards the base of the prism, allowing the eyes to more easily converge and focus on a near object, thus improving near vision alignment.
