Theta Formula

[princess]

From the given prescription , how to find out the power at axis 180? using the Theta formula

Example : -4.50 -3.5 X 40
what is power at 90 axis ?
what is the answer ?


+2.00 +3.00 X 110
what is the power at axis 180 ? using the theta formula

-6.00 +2.00 X 85
what is the power at axis 180?

Please answer these for me as soon as possible
i have a test on this next week

[Robert Martellaro]

From the given prescription , how to find out the power at axis 180? using the Theta formula

Example : -4.50 -3.5 X 40
what is power at 90 axis ?
what is the answer ?


+2.00 +3.00 X 110
what is the power at axis 180 ? using the theta formula

-6.00 +2.00 X 85
what is the power at axis 180?

Please answer these for me as soon as possible
i have a test on this next week

D₉₀ = D_s + D_c*cos²a

D₁₈₀ = D_s + D_c*sin²a

D_s is the sphere power, D_c is the cylinder power, a is the axis.

[HarryChiling]

Theta is aften described as the difference in the meridian in question and the major meridian or sph.

In Roberts equation use the sin version and replace a or axis with the difference in axis as described above.