Color blindness – Causes, symptoms and testing
Color blindness refers to all color vision deficiencies present from birth (congenital). Its scientific name is dyschromatopsia (dys-disorder; chroma-colors; opsia-vision). Color blindness primarily affects boys in the same family; it is therefore a genetic, hereditary disorder, but most often transmitted by the mother (X-linked). The condition results in difficulty distinguishing certain colors, most often green and red, and less frequently blue. The standard tests for confirming color vision deficiency are the Ishihara and Hue tests. Color blindness is not in itself a disability; however, this condition, like high myopia or other ophthalmological conditions, can restrict access to certain professions. The diagnosis is often suggested by the teacher or parents and confirmed by an orthoptist and an ophthalmologist.
What is color blindness?
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The retina functions like a camera: the cornea and the lens allow focusing.
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The retina, on the other hand, is the sensor (film). Color blindness is an impairment of color perception, therefore a disorder of the retina.
A reminder about how the retina works
The retina is a thin membrane of cells lining the back of the eye. It is 0.5 mm thick. There are two types of cells in the retina that detect light. They are called cones and rods:
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Rods only detect contrast, that is, light and dark. They are very sensitive to low light intensities. They primarily serve the visual field.
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Cones detect colors. They are primarily concentrated near the center of your vision because they enable precise and discriminating vision. There are three types of cones, classified according to the color they detect: red, green, and blue cones. It is the information provided by the cones that allows for color perception.
Color blindness
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Color blindness occurs when one or more types of cones are absent or malfunction. Most often, only one type of cone is affected, making it difficult to distinguish between two colors. In the complete absence of cones, color perception is impossible; this is called achromatopsia.
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There are varying degrees of color blindness. Some patients with mild color blindness can see colors normally in adequate lighting but have difficulty discriminating them in the dark. Others cannot distinguish certain colors regardless of the light level.
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Color blindness typically affects both eyes equally and remains stable throughout life. The condition is usually present from birth.
Symptoms of color blindness
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The symptoms of color blindness can range from mild to severe. Many patients have such mild symptoms that they are unaware of their color vision deficiency.
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Most often, it is the parents or the teacher who suggest the diagnosis. In cases of known family history, parents frequently request early screening. However, this screening does not affect the child's schooling or learning.
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The most common symptoms are:
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Difficulties in perceiving colors and their intensity.
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An inability to differentiate between shades of identical or similar colors. Especially with red and green or blue and yellow.
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Except in its most severe form, color blindness does not affect the sharpness of vision, that is, visual acuity. Children with color blindness therefore have visual acuity of 20/20 (10/10) after correction of any myopia or hyperopia.
Achromatopsia – A severe form of color blindness
The inability to perceive any color is called achromatopsia. In this case, the patient perceives everything in shades of gray. This condition is extremely rare, associated with poor vision and the following symptoms:
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Amblyopia – Lazy or weak eye
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Nystagmus – an involuntary, jerky movement of the eye
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Photophobia – Sensitivity to light
Causes of color blindness
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The need for an examination under cycloplegia is determined either after a standard eye exam or routinely for strabismus or as part of a pre-operative assessment. In both cases, two eye exams are always performed: one before and one after instilling the eye drops.
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Most often, this cycloplegic examination is the subject of a later consultation, for reasons of practice organization (avoiding congestion of waiting rooms and delay for subsequent patients) or of the patient, who is not prepared to have blurred vision for the rest of the day.
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During this second consultation, the patient has previously instilled their eye drops, and arrives at the office ready to undergo the examination.
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After the examination, the ophthalmologist explains his findings to the patient and recommends appropriate treatment.
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Depending on the product used, the patient's discomfort lasts for a longer or shorter time, but since he was warned beforehand, he made arrangements accordingly.
Causes of color blindness
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Most patients with color blindness are born with the condition. It is a genetic and congenital disorder.
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Congenital color vision deficiencies are usually passed from mother to son. This is known as an X-linked genetic disorder (X chromosome, transmitted by the mother).
Can girls be affected?
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Yes! However, girls have 2 X chromosomes, so both the father and mother must carry a defective gene and both pass it on to their daughter, which is exceptional.
What other diseases can impair color vision?
Other conditions that cause color vision deficiency are most often acquired. These can include damage to the lens, the retina, or the optic nerve. Examples include:
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Cataracts – Responsible for a yellowing of colors, reversible.
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Maculopathies – CRSC, macular edema, essentially causing blue-yellow dyschromatopsia.
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Optic neuropathies – Damage to the optic nerve: optic neuritis, glaucoma,… giving dyschromatopsia generally red green.
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Some drugs that are toxic to the retina and optic nerve: Plaquenil, antituberculosis drugs (Isoniazid and Ethambutol), Lithium.
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Some toxins, and especially alcohol.
Acquired color vision deficiencies generally tend to worsen as the disease progresses, unlike color blindness, which remains stable.
Who is affected?
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Men are much more at risk than women, who suffer from color blindness only exceptionally.
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It is estimated that one in ten men suffers from some form of color blindness, including mild cases.
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The disease is more common in men of northern European origin.
What are the aggravating factors?
Certain diseases exacerbate color vision deficiencies. The main ones are:
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Glaucoma – Degeneration of the optic nerve.
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Diabetes – particularly macular edema.
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AMD – Age-related macular degeneration.
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Alzheimer's disease.
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Parkinson's disease.
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Chronic alcohol intoxication – Alcoholism.
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Sickle cell disease.
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Retino- and neuro-toxic drugs: hydroxychloroquine (Plaquenil), Isoniazid, Ethambutol,...
Testing and diagnosis of color blindness
Color blindness is usually diagnosed following an orthoptic assessment prior to an ophthalmological consultation. The two tests used are:
The Ishihara test
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These are tiles made up of many colored bubbles forming numbers.
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Depending on the bubbles, some are designed to unmask simulations and others color vision deficiencies.
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This is a screening test that gives a precise idea of the type of color blindness.
The Hue test – Precise color and contrast vision
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The Hue test consists of 15 to 50 numbered tokens of different colors.
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They must be arranged from lightest to darkest in a gradient.
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This test helps determine the axis of dyschromatopsia, that is, the exact type of color blindness.
Treatment for color blindness
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There is no cure for congenital color blindness. The condition does not generally result in a recognized disability; however, a medical certificate is usually helpful for adapting certain school assessments. For example, in geography map tests, the student can complete the assessment with an adapted format requiring them to fill in the maps with patterns rather than colors.
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For several years now, glasses have been available that modify color perception. However, these are not a miracle cure, but rather products adapted to certain forms of color blindness. It is important to try them on before buying them. Currently, there is no reimbursement or coverage from social security. Therefore, you will have to pay the full cost yourself.