1. What is Positive to Negative Cylinder Conversion?

This calculator converts eyeglass prescriptions between positive cylinder and negative cylinder formats while maintaining the same optical effect. This is useful when comparing prescriptions or when a specific format is required.

2. How Does the Conversion Work?

The conversion uses these mathematical transformations:

Where:

• Sphere — The spherical power of the lens
• Cylinder — The cylindrical power (must be positive for this conversion)
• Axis — The orientation of the cylinder (0-180 degrees)

Explanation: The conversion maintains the same refractive error correction while changing the mathematical representation of the prescription.

3. Importance of Cylinder Conversion

Details: Some optical systems or practitioners prefer one format over the other. Being able to convert between them ensures accurate interpretation of prescriptions.

4. Using the Calculator

Tips: Enter the sphere power, positive cylinder power, and axis. The calculator will output the equivalent prescription in negative cylinder format.

5. Frequently Asked Questions (FAQ)

Q1: Why convert between formats?
A: Different practitioners and regions may use different conventions. Conversion ensures consistency.

Q2: Does the conversion change the actual prescription?
A: No, it's mathematically equivalent - just represented differently.

Q3: What if my cylinder is already negative?
A: This calculator is specifically for converting positive cylinder to negative format.

Q4: Why does the axis change?
A: The axis rotates by 90° because the cylinder sign flip requires compensating for the orientation.

Q5: Is there a difference in optical performance?
A: No, both formats produce identical optical correction when properly converted.