CPF lens

A CPF lens is one of a numbered series of yellow to red absorptive lenses that block ultraviolet and short-wavelength visible light, used in low vision to ease glare and light sensitivity. The letters stand for Corning protective filter. The number gives the approximate wavelength below which the lens absorbs, so a CPF 527 blocks most light shorter than 527 nm.¹ The original lenses are photochromic glass, so each also darkens outdoors. A CPF 511, for example, passes about 44 percent of light indoors and 14 percent outside.¹

The CPF 511 and 527 are often chosen for cataract, macular degeneration and corneal dystrophy, and the 550 for retinitis pigmentosa and severe light sensitivity. Benefit is mostly subjective.¹ In one study, acuity in normal and low-vision patients was the same through a CPF 527, a gray filter of equal darkness and a plain lens.² In another, which measured contrast acuity under glare, patients with anterior-segment disease did better with CPF filters than with gray, probably because the filters reduce scatter inside the eye.³