6.1 Ophthalmic Prism

How do you calculate the angle of deviation for a prism??

d=A(n-1)

A=apical angle

Where is light deviated toward in a prism?

toward the base

Where is the image moved toward in a prism?

toward the apex/away from the base

What is a prism diopter?

deviation in cm at a distance of 100cm (1m)

How do you get prism diopters from an angle in degrees?

pd=100 tan (degrees)

What is yolked prism?

both prisms are in the same cardinal directiosn (R/L/U/D) in equal amounts

If both prism are in the same cardinal direction in equal amounts (yolked prism) how does this affect eye movement and ocular convergence?

eyes move in same direction

ocular convergence does not change

If bases are in opposite cardinal directions, how does this affect eye movements?

eyes will move in opposite directions

How does BI prism over both eyes affect ocular convergence?

increases ocular divergence (decreases convergence demand)

How does BO prism over both eyes affect ocular convergence?

increases ocular convergence

What does prism change and what does it not change?

changes vergence demand of target

does not change accommodative demand of target

If horizontal prism are not in the same cardinal direction, how do you calculate vergence demand?

add the two prism powers together

What is the resultant prismatic effect on vergence if prism are in the same cardinal direction, but different prism powers?

difference in prism power with the higher prism power determining direction

If a patient is given un-needed BO prism, what deviation will they have?

exo deviation

If a patient is given un-needed BI prism, what deviation will they have?

eso deviation