Station three
(allowed 5 minutes)
aa
 Perform toric transposition of the following:   a. +3.00 / -1.00 X 180 to the base curve + 6 D b. -2.00 / +1.50 X 90   to the base curve - 6D

 Answer to a -4.00DC / +6.00DC X 180 / +7.00X 90 Step one: First transpose the cylinder so that it is the same sign as the base curve. +3.00 / -1.00 X 180 becomes +2.00 / +1.00 X 90 Step two: The required spherical surface is obtained by subtracting the base curve power from the spherical power above and this give +2 - (+6) = -4 DS Step three: Specify the axis of the base curve. This is 90 degrees to the axis of the required cylinder and represent the weaker principal meridian of the toric surface. The value is: +6.00 X 180 Step four Add the required cylinder to the base curve power and this give: +6D +1D = +7.00 X 90 The complete toric formula is -4.00DS / +6.00DS X 180 /+ 7.00 X90   Answer to b +5.50DS / -6DS X 90/ -7.50DS X 180 Step one: -2.00 /+1.50 X 90 =  -0.50 / -1.50 X 180 Step two Required spherical surface is -0.50 - (-6) = +5.50 DS Step three: -6.00 DS X 90 Step four: -6.00 + (-1.50) = -7.50DS X 180 The final toric formula is +5.50DS / -6DS X 90 / -7.50DS X 180