In a cylinder or spherocylinder lens, what do the two meridians correspond to?

In a cylinder or spherocylinder lens, the two meridians correspond to maximum and minimum powers. This concept is crucial in understanding how cylindrical lenses, which are used to correct astigmatism, function.

A cylindrical lens has varying powers in different orientations, with one meridian providing the maximum optical power and the other providing the minimum optical power. This variation allows the lens to correct vision for astigmatism, which occurs when light rays fail to focus evenly on the retina due to the irregular shape of the eye.

Choosing the correct meridian includes aligning the lens to the appropriate axis, thus ensuring that the maximum power counteracts the astigmatism effectively. The difference between the maximum and minimum powers is known as the cylinder power, which plays a significant role in the prescription of corrective lenses for patients with astigmatism.

The other options refer to distinct aspects that do not accurately describe the function of the meridians in cylindrical lenses. For example, maximum and minimum thickness pertains to the physical dimensions of the lens rather than its optical characteristics. Shape and curvature involve the general form of the lens but do not specifically relate to power variation across meridians. Similarly, the reference to the optical center and edge relates more