Which type of lens characteristic specifically addresses astigmatism?

The characteristic that specifically addresses astigmatism is cylinder power. Astigmatism occurs when the curvature of the cornea or lens is not uniform, leading to multiple focal points. To correct this condition, lenses must have a component that counteracts the unequal curvature. This is where cylinder power comes into play.

Cylinder power refers to the additional lens power that is needed to correct the astigmatism by introducing a particular amount of curvature in one meridian of the lens. The cylinder lens has different powers in different orientations, allowing it to effectively compensate for the distortion caused by astigmatism. By adjusting the cylinder power in prescription lenses, an optician can help focus light appropriately onto the retina, thus improving visual clarity for individuals with astigmatism.

The other characteristics mentioned, such as base curve, prism power, and index of refraction, while important in lens design and function, do not specifically target the correction of astigmatism. The base curve relates to the overall curvature of the lens and impacts fitting and comfort, prism power addresses the horizontal or vertical alignment of light for binocular vision issues, and the index of refraction refers to the material's ability to bend light, which affects lens thickness and weight but does not