1. What is Cylinder Conversion?

Cylinder conversion is the process of changing the sign of the cylinder power in an eyeglass prescription while maintaining the same optical effect. This is often needed when switching between plus and minus cylinder formats.

2. How Does the Calculator Work?

The calculator uses the following formulas:

Where:

• Old Sphere — Original sphere power (D)
• Old Cyl — Original cylinder power (D)
• Old Axis — Original axis (degrees)

Explanation: The conversion maintains the same refractive error but expresses it differently by redistributing the power between sphere and cylinder components.

3. Importance of Cylinder Conversion

Details: Accurate cylinder conversion is crucial when comparing prescriptions, switching between lens manufacturing systems, or verifying prescription consistency.

4. Using the Calculator

Tips: Enter the original sphere, cylinder, and axis values. The calculator will automatically compute the converted values. All values must be valid (axis between 0-180 degrees).

5. Frequently Asked Questions (FAQ)

Q1: Why convert cylinder values?
A: Different optical systems use different cylinder formats. Conversion ensures the same optical correction is maintained.

Q2: Does the conversion change the prescription's effect?
A: No, the optical effect remains identical - only the mathematical expression changes.

Q3: How does axis change during conversion?
A: The axis is rotated by 90 degrees (modulo 180) when the cylinder sign is flipped.

Q4: Are there limitations to this conversion?
A: The conversion is mathematically exact for all valid prescriptions. However, very high cylinder powers might have practical limitations in lens manufacturing.

Q5: Is this conversion used in contact lens prescriptions?
A: The same mathematical principles apply, but contact lens prescriptions often have additional parameters that need consideration.