What is the residual astigmatism for this patient?

• A. -0.50 x 90
• B. -0.25 x 180
• C. -0.75 x 180
• D. 0.00 x 180

Answer: (B)

Residual astigmatism is what remains after a gas-permeable lens has corrected the corneal cylinder during wear. With GP lenses, you aim to neutralize the corneal toricity, so the residual is the small amount of cylinder that persists due to noncorneal factors or imperfect neutralization.

A small residual of 0.25 diopters at axis 180 is consistent with a largely successful GP correction that leaves only a tiny amount of astigmatism along the horizontal meridian. This level is plausible after fitting, and the axis shows where that remaining cylinder sits.

The other possibilities imply larger residual errors or a different axis that would typically produce more noticeable blur or require a lens redesign, making them less likely in this scenario. Therefore, the residual astigmatism best fits as -0.25 x 180.