When you increase power on a PAL, this creates:

• A. Reduced field of view
• B. No change in aberrations
• C. Surface astigmatism
• D. Central prismatic effect

Answer: (C)

Increasing power in a progressive lens changes how the lens surface is curved in two principal meridians. To create the gradual change from distance to near, the lens must bend more in one direction than in the other. As the addition gets larger, the difference between the meridional curvatures grows, so the surface itself becomes more astigmatic. This is what we mean by surface astigmatism—the lens surface imposes different refractive powers in perpendicular meridia, especially away from the central region. Other effects like a simple reduction in field of view aren’t the direct consequence of higher add power, and while aberrations can change with power, the characteristic outcome described here is the surface-level astigmatism introduced by the toric surface needed for the progression.