Color blindness

Color blindness is classified by the specific cone photopigment that is missing or altered. The most common forms are red-green deficiencies, including protanopia (absence of red cones), deuteranopia (absence of green cones), and their milder variants protanomaly and deuteranomaly. Blue-yellow deficiency (tritanopia) is rare and not sex-linked. Complete color blindness, or achromatopsia, is extremely rare and involves total absence of cone function, leading to poor visual acuity and light sensitivity³.

The inherited forms are typically caused by mutations in the OPN1LW and OPN1MW genes on the X chromosome, which encode the red and green cone opsins. Because males have only one X chromosome, they are more likely to express the trait. Females can be carriers or affected if both X chromosomes carry the mutation. Tritanopia is linked to chromosome 7 and affects both sexes equally⁴.

Diagnosis of color blindness is typically performed using the Ishihara test, which consists of plates with colored dots forming numbers or patterns that are invisible to those with red-green deficiencies. The Farnsworth-Munsell 100 Hue test and the Hardy-Rand-Rittler test provide more detailed assessments of the type and severity of the deficiency⁵.

In clinical settings, anomaloscopy is considered the gold standard for diagnosing red-green deficiencies, as it requires the patient to match a mixed color to a reference. Genetic testing can identify specific mutations, but it is not routinely used for diagnosis. Screening is often performed in schools or during routine eye exams, but many individuals remain undiagnosed because the condition does not affect visual acuity⁶.

Color blindness can affect everyday tasks such as interpreting traffic lights, reading maps, selecting ripe fruit, and matching clothing. In some professions, such as piloting, electrical wiring, and graphic design, normal color vision is required, and color-blind individuals may face restrictions. However, many adapt by using brightness, position, and texture cues to compensate.

Technological aids include color-correcting glasses (e.g., EnChroma) that filter specific wavelengths to enhance color contrast, and smartphone apps that identify colors via camera. These tools do not restore normal color vision but can improve discrimination. In education, teachers can use patterns and labels alongside colors to ensure accessibility⁷.

Color blindness has notable historical and scientific dimensions. The term 'Daltonism' derives from John Dalton, the chemist who described his own red-green deficiency in 1794; his preserved eye was later analyzed for DNA in 1995, confirming deuteranopia³. In animals, color vision varies widely: many mammals are dichromats, while birds and bees have tetrachromatic vision, perceiving ultraviolet light.

Acquired color vision deficiency can result from conditions such as diabetes, multiple sclerosis, or exposure to industrial chemicals like carbon disulfide. Some studies suggest that color-blind individuals may have enhanced abilities in certain visual tasks, such as detecting camouflage or texture differences, due to neural plasticity. Additionally, the prevalence of color blindness is lower in populations of African or Asian descent compared to those of Northern European origin¹.

Cone cells

Photoreceptor cells in the retina responsible for color vision.

Protanopia

Absence of red-sensitive cones, causing red-green confusion.

Deuteranopia

Absence of green-sensitive cones, causing red-green confusion.

Tritanopia

Absence of blue-sensitive cones, causing blue-yellow confusion.

Achromatopsia

Complete absence of cone function, resulting in total color blindness.

Ishihara test

A common screening test using colored dot plates.