What is a common pitfall when recording lens parameters on a prescription?

• A. Verifying PWR values
• B. Mixing up sphere/cylinder signs
• C. Recording base curve and diameter correctly
• D. Using consistent units

Answer: (B)

The key idea here is how signs for sphere and cylinder work together on a prescription. The sphere power represents the overall focus error, while the cylinder power corrects astigmatism along a specific meridian. Cylinder can be written with a plus or minus sign depending on the notation system being used, and when you convert or transcribe an Rx, it’s easy to mix up these signs. If the cylinder sign is recorded incorrectly or swapped with the sphere, the lens is prescribed with the wrong correction in different meridians, leading to blur, eye strain, or poor lens performance, especially with toric soft contacts where precise toricity and axis are critical. Always check that the cylinder’s sign matches the notation system in use and is recorded in the correct place so the intended astigmatic correction is preserved.