Color blindness or color vision deficiency is a disorder in which there is a decreased ability to spot colour differences & recognize colors.
- Inability to properly separate & limited variability in the red-green color axis.
- For eg: People with dichromacy have difficulty in distinguishing a green apple from a red apple & from a red traffic light with the green traffic light.
- Inability to distinguish between red/amber traffic lights & yellow street lamps.
- In total color blindness, there is a total inability to distinguish between colors & hence everything is seen as either black or white.
- Light sensitivity
- Involuntary movement of the muscles of the eye.
- Poor vision.
CAUSES & RISK FACTORS FOR COLOR BLINDNESS
Inherited disease/Genetic factors: Color blindness occurs due to a mutation in the X chromosome.
Some of the inherited diseases are:
- Cone dystrophy
- Cone-rod dystrophy
- Achromatopsia (also called rod monochromatism)
- Blue cone monochromatism (also called blue cone monochromacy)
- Leber’s congenital amaurosis
- Retinitis pigmentosa (initially affects rods but can later progress to cones and therefore color blindness).
Classification on the basis of color deficiencies & mechanism
- Monochromatic: Total color blindness caused to to damage & absence of cone cells.
a) Rod monochromacy: Result of non-functioning retinal cones.
b) Cone monochromacy: Damage of more than one cone in the retina or presence of more than one type of dichromatic color blindness.
a) Protanopia: Caused due to complete loss of red retinal receptors.
b) Deuteranopia: Presents an additional dimming effect along with the preceding symptoms of protanopia.
c) Tritanopia: Total absence of blue retinal receptors.
- Anomalous trichromacy: One of the three cone pigments is altered in the spectral sensitivity.
a) Protanomaly: Altered sensitivity of red retinal receptors & variability in the red-green hue.
b) Deuteranomaly: Altered sensitivity of green retinal receptors & mild variability in the red-green hue.
c) Tritanomaly: Affecting blue-green & red-yellow hue.
Acquired Causes/Other Risk factors:
- Drug/chemical mediated:
a) Hydroxylchloroquin, used for malaria
b) Ethambutol, used for treatment of TB
d) Organic solvents
- Disease/Disorder related:
b) Swelling of the occipital lobe
c) Damage to the retina due to exposure to UV radiation.
d) Age related degeneration
f) Vitamin A deficiency
g) Chronic solvent-induced encephalopathy (CSE), caused by long-time exposure to solvent vapors.
DIAGNOSIS OF COLOR BLINDNESS
- Ishihara color test: The test most commonly used for diagnosis of red-green color defect. It utilizes colored numbers.
- Anomaloscope is used for diagnosis of color anomaly.
- Farnsworth Lantern Test: Developed for the US Navy.
- Farnsworth–Munsell 100 hue test, used to measure chromatic discrimination, therefore the patient is asked to arrange a set of colored caps or chips to form a gradual transition of color between two anchor caps.
- HRR color test is a green-red color test.
There are no treatments currently for color blindness:
- Drug acquired color blindness may subside after stopping of the use of the drugs responsible.
- Treatment & management of disorders may or may not prevent color blindness.
- The most common form pf management is use of colored spectacle lenses or use of wavelength lenses, which may help in identifying some colors.
- Many mobile and computer applications have been developed to help color blind individual to view better/differentiate between colors.
MANAGEMENT & REMEDIES
- Labeling of essential material & objects.
- Putting stuff in a particular order that can be easily memorized.
- In certain countries like Canada, UK, Netherlands, traffic signals/lights are aligned in a horizontal fashion with every light (Red, yellow, Green) is a different shape.