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The component of a lens prescription that has the same refractive power in all meridians. It is responsible for correcting Myopia (nearsightedness, expressed as negative power) or Hyperopia (farsightedness, expressed as positive power).
read more about spherical power ...A spherical lens has surfaces that are segments of a sphere, causing light rays to converge or diverge to a single focal point (or theoretical focal point).
Measured in Diopters ($D$). The power is the inverse of the focal length (in meters).
In a prescription, the spherical power (Sphere or SPH) is always listed first (e.g., $-2.50 D$ is $2.50$ diopters of myopia).
Spherical power focuses light equally in all meridians. Cylinder power (for astigmatism) has zero power in one meridian and maximum power 90 degrees away.
A plano lens has zero spherical power ($0.00 D$) and is used for non-prescription sunglasses or readers.
Positive spherical power (convex lens) causes light to converge before the eye, used to correct hyperopia or presbyopia.