In this context, what is the maximum residual astigmatism that would still allow wearing a spherical GP lens?

• A. 0.75D
• B. 0.25D
• C. 1.00D
• D. 0.50D

Answer: (A)

Small residual astigmatism can be tolerated with a spherical GP lens because the tear film under the lens forms a smooth, nearly spherical surface that helps mask some of the corneal cylinder. This tear lens effect, combined with the spherical front of the GP lens, can neutralize a portion of astigmatic error so vision remains reasonably sharp.

When residual astigmatism is about 0.75 diopters or less, a spherical GP lens can still provide acceptable acuity for many wearers. If the residual exceeds that amount, the blur becomes too evident for a spherical design to compensate, and a toric GP lens or other specialty design is usually indicated.

So, the maximum residual astigmatism that would still allow wearing a spherical GP lens is around 0.75D. Smaller residuals (0.25D or 0.50D) would also work, but the question asks for the upper limit.