Back and bitoric lenses will have two base curves far from each other; front torics will have one base curve. Which lens type does this describe?

• A. Spherical lenses
• B. Front torics
• C. Toric lenses
• D. Back toric

Answer: (C)

Toric lenses. These lenses correct astigmatism by having different curvatures in different meridians. In back-surface toric or bitoric designs, there are two distinct back surface curvatures (two base curves) that are set far apart, which creates the needed toricity and helps the lens align with the corneal astigmatism and stay stable on the eye. Front-toric designs achieve toricity mainly through the front surface and typically rely on a single back curve. Spherical lenses, by contrast, have a single, uniform curvature and don’t correct astigmatism.