11 - Prism Effect on Lens Thickness

Question 1

Does Prism affect the lens thickness?

Answer 1

Yes

Question 2

How much thicker is the lens to be assumed when prism is present? 3

Answer 2

one half of the prism thickness difference
or 1/2 g when prism is present (Regardless of how the prism base is orientated)

Question 3

What does the Base direction determine when considering thickness of lenses + prism?

Answer 3

How much the prescribed prism will change the center or edge thickness.

Question 4

How is thickness affect in a plus lens with Base In prism?

Answer 4

Center thickness increases by one half of the prism thickness difference.

Question 5

How is thickness affect in a plus lens with Base Out prism?

Answer 5

Center thickness decreases by up to the full thickness difference, depending on the amount of decentration present.

Question 6

How is vertical prism affected in a plus lens with a small B measurement?

Answer 6

Center thickness will not change

Question 7

How is vertical prism affected in a plus lens with a large B measurement?

Answer 7

Center thickness increases by up to one half the thickness difference.

Question 8

What does this formula find? g=dP/100(n-1)

Answer 8

The difference in thickness between the apex and base of the prism.

Question 9

What do the letters stand for in g=dP/100(n-1)?

Answer 9

P=the amount of prism
n=the refractive index of the lens material
g=the difference in thickness between the apex and base of the prism
d=the distance between the apex and the base of the prism

Question 10

Try and match the frame PD to the Patient PD to avoid decentration in? T/F

Answer 10

True

Question 11

See powerpoint 11 last two pages to review