prism peter Flashcards
(50 cards)
What does a relieving prism do?
Displaces the image toward the direction the eye turns
Prism Base
A prism is placed before the eye with reference to the base
3 Effect of a prism on light
Displacement, Dispersion, Deviation
Effects of prism on light
Prism will have no focal length and light will deviate toward the base
The_____ the prism the ______ the light will _____ and the _____ the image will be ______
Stronger, more, Deviate, More, Displaced
Strabismus (heterotropia)
When one eye is not aligned with the other eye to look in a different direction
What is Adverse Prism?
Stimulate an eye muscle to work harder, designed to strengthen weak muscles
Who came up with Fresnel Prism
French physicist, Augusti Jean Fresnel
What is Dissociating Prism
Affect temporary interference with a fusion of both eyes, use of risley prisms in phoropter
Base
Compounding Situations
Base up and Base down
Base in and Base in
Base out and Base out
What is the Prismatic effect?
visual discomfort when optical centers are not situated over the pupils
What is Excessive Base down?
Makes people and vertical objects seem taller than they are
Excessive Base Up
Makes people and vertical objects seem shorter than they are
4 different prism power units
Deviating Angle, Prism Diopter, Centrad, Apical
What is the Rule of Thumb for 45° off axis?
50% of cylinder power
What unit is used to measure prism power in optics?
Prism diopter (∆)
What is the apex of a prism?
The edge where two prism surfaces meet
What is the patient’s reaction to excessive prism?
Discomfort, dizziness, and spatial distortion
What is one drawback of Fresnel prisms?
Reduced visual contrast
What happens with excessive BD prism?
Objects appear concave; patient feels like standing in a bowl
Base
Cancelling situations
Base up and base up
Base down and base down
Base in and base out
What does a 1 prism diopter do to light?
Deviates light 1 cm at 1 meter distance
What is the formula for decentration from prism power?
Dec = 10 × ∆ / D
Why add 2mm in MBS calculation?
To compensate for edge chipping or defects