The person is suffering from an eye defect called myopia. In this defect, the image is formed in front of the retina. Hence, a concave lens is used to correct this defect of vision.
Object distance, u = infinity =∞
Image distance, v = −80 cm Focal length = f
According to the lens formula,
A concave lens of power −1.25 D is required by the person to correct his defect.