Color blind glasses

Color blind glasses or color correcting lenses are light filters, usually in the form of glasses or contact lenses, that attempt to alleviate color blindness, by bringing deficient color vision closer to normal color vision or to make certain color tasks easier to accomplish. Despite its viral status, the academic literature is generally skeptical of the efficacy of color correcting lenses.

Color blindness (color vision deficiency) is the decreased ability to see color or differences in color. It can impair daily color tasks such as selecting ripe fruit or choosing clothing, as well as safety-related tasks such as interpreting traffic lights. While the disability of color blindness is considered minor, the use of color in safety systems excludes the color blind from many occupations. Screening for color blindness in these occupations is accomplished with color vision tests, often the Ishihara test. There is no cure for color blindness, but management of color vision may be possible with apps or color correcting lenses.

There are several kinds of lenses that claim to increase accuracy in color-related tasks. The lenses may be eyeglasses, contact lenses or handheld lenses, and may be distinguished according to their working principle. Most lenses are intended for red-green color blindness, though some lenses are also marketed for blue-yellow color blindness. All lenses are passive optical filters, so can only subtract/attenuate selective wavelengths of light. However, there are large variations on this theme:

The idea of using colored filters as color correcting lenses originated from August Seebeck in 1837. In 1857, James Clerk Maxwell constructed red and green glasses according to Seebeck's theory. Seebeck noticed that red and green lenses change the relative luminosity of colors that the red-green colorblind usually saw as metamers and the subjects could thereby estimate the correct color. Based on these results, Maxwell hypothesized that color perception would improve after prolonged exposure to the glasses.

Red-green disparately tinted lenses are not currently commercialized, likely because the resulting color vision is highly distorted (making color-naming tasks difficult) and the different lens colors are not aesthetic. However, a modern Swedish invention called the SeeKey uses red and green lenses to help the user identify colors. The lenses are not worn over the eyes, but are handheld. The user alternates looking between the two lenses and can infer a color by the relative brightness changes between the two lenses and direct vision. For example, red-green colorblind subjects routinely confused green and orange; using the SeeKey, orange would appear lighter through the red filter and darker through the green filter (relative to no filter). Using the lenses during the Ishihara test achieve a 86% improvement. Unlike other color correcting lenses, the SeeKey is not intended to be worn consistently, and is only used when required for a color task.

Monocular lenses are usually red-tinted contact lenses worn over a single (the non-dominant) eye. These lenses are intended to leverage binocular disparity to improve discrimination of some colors. Compared to disparate lenses, one eye is left unfiltered in order to preserve a realistic perception of colors. Examples of this technology include X-chrom (1971; manual) and Chromagen (1998).

A 1981 review of various studies to evaluate the effect of the X-chrom contact lens concluded that, while the lens may allow the wearer to achieve a better score on certain color vision tests (specifically pseudoisochromatic plates like the Ishihara test), it did not correct color vision in the natural environment. or practical industry. The improvements in pseudoisochromatic plates is from a selective (for some colors) change in brightness, thereby introducing achromatic contrast to the images, rather than an increase in chromatic contrast. In fact, despite the claim of binocular disparity leading to color vision improvements, Ishihara test results actually improved when the dominant (unfiltered) eye was covered during the test.

Although still on the market, monocular filters are considered obsolete, since they lead to reduced visual acuity, changes in apparent velocity perception, visual distortions (such as the Pulfrich effect) and an impairment of depth perception. These side effects can make monocular lenses a liability when intended as a solution to color blindness.