Colour Vision Deficiency — CVD, also known as colour blindness

The most frequent type involves red-green deficiencies, which come in two main forms: dichromacy, where either red or green cone cells fail completely, and anomalous trichromacy, where those cells function partially but not normally.

Those affected may perceive these colors as noticeably duller than individuals with typical vision. In cases involving red sensitivity, red tones might be mistaken for black or dark shades. The way someone experiences this condition varies widely based on how well their cone cells operate.

Red-green CVD follows a hereditary pattern passed through families. Genes carry instructions essential for proper cell development; when mutations occur, these signals become flawed, leading to malfunctioning cone cells responsible for detecting red or green light.

The genetic defect linked to red-green CVD is transmitted via an X-linked inheritance model, placing the faulty gene on the sex chromosomes. Since males inherit only one X chromosome—from their mother—if that chromosome carries the mutation, they will develop the condition.

In contrast, blue-yellow CVD affects shorter-wavelength vision more rarely and arises when blue cone cells are compromised. Unlike its red-green counterpart, it doesn’t follow an X-linked pattern and impacts both genders equally, though it remains uncommon, influencing fewer than one percent of people overall.

Two extreme conditions—monochromatism and achromatopsia—involuntary loss of all color vision due to inherited disorders affecting retinal cone functionality.

Achromatopsia occurs approximately once every thirty thousand individuals, resulting from multiple identified gene disruptions preventing cones from operating correctly. Complete achromatopsia means no functional cone activity whatsoever, while partial versions allow limited residual color perception despite significant impairment.

Additionally, blue cone monochromatism represents another rare disorder wherein only blue-sensitive cones remain active. Prevalence stands below one in one hundred thousand cases and typically manifests alongside visual challenges like heightened light sensitivity, involuntary eye movements (nystagmus), blurred vision, and nearsightedness starting at birth.