Final answer:
Single vision sphero-cylinder lenses with power in all meridians are used to correct astigmatism by providing clear vision through correcting uneven focus.
Step-by-step explanation:
Single vision sphero-cylinder lenses with power in all meridians are used to correct astigmatism. Astigmatism is a vision defect characterized by uneven or asymmetrical focus of the eye. This can be due to irregularities in the shape of the cornea, lens irregularities, or unevenness in the retina. These lenses have different powers in different meridians to correct the uneven focus and provide clear vision.