Congenital color blindness refers to a group of disorders that alter color vision, and these can be found in approximately 10% of the population.
Trichromats are individuals with normal color vision who have three types of normal cones: red or L-cones (long-wavelength sensitive; described first and thus designated as “prot”); green or M-cones (middle-wavelength sensitive; described second and thus designated as “deuter”); and blue or S-cones (short-wavelength sensitive; described third and thus designated as “trit”). A color vision defect occurs if one or more types of cones have a lack (anopia) or abnormality (anomaly) of photopigment.
The severity of abnormal color perception varies depending on the type of color deficiency. The most frequent form is red-green, which is inherited in an X-linked recessive fashion and is therefore more common in men. An abnormality in color vision does not cause decreased visual acuity (except for rod and blue cone monochromatism) or an abnormal retinal appearance.
The classification of color defects is as follows:
- Congenital Dichromatism (lack of one color photopigment):
- Protanopia: lack of red-sensitive photopigment
- Deuteranopia:lack of green-sensitive photopigment
- Tritanopia: lack of blue-sensitive photopigment
- Anomalous Trichromatism (abnormal color photopigment (altered spectral absorption) in one of the cone types):
- Protanomaly: abnormal red-sensitive photopigment
- Deuteranomaly: abnormal green-sensitive photopigment
- Tritanomaly: abnormal blue-sensitive photopigment
- Rod Monochromatism (congenital achromatopsia; absence of cone function, normal rod function): No color vision, poor central vision, nystagmus, and photophobia present from birth; macular pigment abnormalities.
- Cone Monochromatism (atypical achromatopsia; only one type of cone (usually blue)): cannot dicriminate color.
Until recently, there was no treatment for color blindness. However, a new lens technology, EnChroma, allows patients with some forms of red-green color blindness (i.e. protanomaly and deuteranomaly) to better perceive these colors. These patients see colors differently because the absorption spectra of their red and green photopigments overlap more than normal. The extent of color deficiency they experience is directly related to the amount the cone signals overlap. Their eyes are otherwise healthy, and their neural pathways for processing color are intact, so they are just receiving improper information.
To remedy this situation, EnChroma has developed tinted lenses with multi-notch filters to selectively block light with specific wavelengths that correspond to the maximum overlap between the red and green photopigments. This increases the separation between the red cone and green cone signals and thus provides better color vision to those with a red-green deficiency.
Although this technology is not a cure for disease, it can have a profound effect on patients with red-green color blindness. The first version of EnChroma lenses was released in 2012, and the company subsequently updated the lenses from glass to plastic with full prescription capability in 2014. These glasses are now available in five different designs, or the lenses can also be put in to the patient’s own frames.