Transpose the prescription
-0.75DS/-3.25DCx30 to the toric form with a capstan-form surface which has a +2.50D base curve
Try this
http://www.opticampus.com/files/introduction_to_ophthalmic_optics.pdf
Thank you but I have already been on this website and did not find an example of capstan transposition...Are you able to help at all?
I have transposed the prescription so that it has a plus cyl as we are given a plus base curve=
-4.00DS/+3.25DCx120
what do i do next?
-6.5 DS/ +2.50x130/+5.75x120
To transpose the prescription into the toric form with a capstan-form surface having a +2.50D base curve, follow these steps:
Step 1: Understand the prescription notation
The prescription -0.75DS/-3.25DCx30 can be broken down as follows:
-0.75 - Sphere power (DS)
-3.25 - Cylinder power (DC)
30 - Axis (x)
Step 2: Determine the base curve for the capstan-form surface
The base curve is +2.50D in this case. The base curve represents the power of the curvature of the lens surface.
Step 3: Transpose the sphere power
To transpose the sphere power, subtract the difference between the desired base curve and the original base curve from the original sphere power.
In this case, the original base curve is 0D (since there is no base curve mentioned) and the desired base curve is +2.50D.
New sphere power = -0.75 - (2.50 - 0) = -0.75 - 2.50 = -3.25
So, the new sphere power is -3.25.
Step 4: Transpose the cylinder power and axis
To transpose the cylinder power and axis, the original prescription needs to be calculated on the new base curve.
To calculate the new cylinder power and axis, use the following formula:
New cylinder power = (Original cylinder power) * (New base curve) / (Original base curve)
In this case, the original cylinder power is -3.25 and the original base curve is 0D.
New cylinder power = (-3.25) * (2.50) / 0 = undefined
Since dividing by zero is not possible, the new cylinder power cannot be calculated in this case.
Therefore, the prescription cannot be transposed into the toric form with a capstan-form surface having a +2.50D base curve, as the calculation for the new cylinder power results in an undefined value.