Progressive spectacle lenses, also called progressive addition lenses, are used in eyeglasses to correct presbyopia and other disorders of accommodation. Thus, wearers can adjust the additional lens power required for clear vision at different viewing distances by tilting their head to sight through the appropriate part of the vertical progression. And the lens location of the correct addition power for the viewing distance usually only requires small adjustments to head position, since near vision tasks such as reading are usually low in the visual field and distant objects higher in the visual field. The other merit of progressive glasses is that this specialized lens surface provides an accurate power distribution for both near and distant vision and reduces the number of optical aberrations. But, progressive lenses suffer the disadvantage of the power progression creating regions of aberration away from the optic axis, yielding poor visual resolution (blur), which varies in relation to the quality of the lens. What else, because of the compromise in vertical range of undistorted vision, there is an inherent impact on peripheral vision with progressive lenses which is more obvious than that which is found in single vision lenses.
