transpositions

Question 1

positive and negative forms of lenses

Answer 1

neg- specify positive power first and axis along most positive power

positive- specify most negative power first and axis is along the most negative power

Question 2

negative to positive sphere cyl form

Answer 2

add sphere to the cyl
change the sign
add or take 90 from axis

Question 3

sphere cyl to crossed cyl

Answer 3

cyl 1= keep sphere same and add or take 90 from axis
cyl 2= add sphere and cyl and axis is same as original

Question 4

crossed cyl to sphere cyl

Answer 4

sphere= most positive cyl
cylinder= least positive- most positive cyl
axis= of the most negative cyl

Question 5

toric lenses front and back

and what is sphere base and cross curve

Answer 5

front always positive
back always negative

sphere curve= spherical surface
base curve= lowest power
cross curve=highest power

Question 6

toric to sphere cyl form

Answer 6

1) add sphere curve to first cylinder power w same axis
2) add sphere curve to second cylinder power w same axis
3) convert crossed cylinders to sphere cyl

Question 7

sphere cyl to toric when sphere curve is specified

Answer 7

1)Convert to crossed cylinder form
2)Subtract spherical surface from each power
3)Keep axis same
Put into thing. Remember front is positive. sphere=sphere

Question 8

Sphere cyl to toric when base curve is specified

Answer 8

Transpose to same sign as base curve
Base curve+90 onto cyl axis
Cross curve= base curve+cyl power. Axis same as cyl axis.
Sphere curve= sphere-base curve