Depending if you go to an ophthalmologist or optometrist your prescription (Rx) will look different.
1.Ophthalmologist Rx are in a plus form : -3.00+1.00 x 180
2.Optometrist Rx are in minus form: -2.00-1.00 x 090
Believe it or not your looking at the same Rx. Optician used the optometrist version. This is the one I will be referring once I show you how to convert #1 to #2.
Its very simple.
- The first number called the sphere is added to the second number which is the cylinder.
- -3.00+1.00= -2.00 this is now your sphere
- The second number (cylinder) will be converted from plus to a minus. +1.00=-1.00 this is now your cylinder.
- The last number is your axis. The axis can only go from 1 through 180(zero).What ever number the axis is it will be added 90 of subtracted 90. In this case its 180-90=90 and this is your new axis.
- Final answer is -2.00-1.00 x 090
Where will the thickness be in the lens?
Unless you have a spherical Rx your lenses will not be the same thickness all around.
For example -2.00 -1.00 x 090
The total power on this lens is a -3.00. This is the sphere and the cylinder together. Your axis is the one that determines where that extra thickness going to be placed. The -2.00 will be at 090 (top and bottom). The -3.00 will be at axis 180 (on the sides).
Example 2: -4.75 -1.00 x 65
The total power on this lens is -5.75. This is by adding -4.75 -1.00= – 5.75. The sphere -4.75 will always be at the axis it was given in this case axis 65. This means the total thickness will be 90 degrees away. 65+90= 155. Looking at the cross below, you can see it will be place at an angle or corner of the lens.
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