What type of lens correction is specified by Cylinder Power?

Cylinder Power specifically refers to the correction required for astigmatism, which occurs due to an irregular shape of the cornea or lens in the eye, causing light to focus on more than one point. The cylinder value measures the degree of astigmatism and is used to determine how much correction is necessary to focus light evenly onto the retina.

Astigmatism does not affect a person's ability to see near or distance objects uniformly; rather, it causes blurriness and distortion at all distances. Therefore, when lens prescriptions include a cylinder power value, it indicates the presence of astigmatism that needs correction, making it the primary reason this answer is correct.

In contrast, near vision refers to the clarity of vision at close range, distance vision concerns clarity at far distances, and presbyopia is an age-related condition affecting the ability to see close objects, which may require bifocal or multifocal lenses. Each of these conditions may require different types of lens corrections that do not specifically rely on cylinder power measurements.