Color Vision Deficiency: Causes, Types, Treatment
Color vision deficiency, also known as dyschromatopsia, is a general term referring to various vision disorders characterized by a deficiency in color perception. The disorders in patients diagnosed with color vision deficiency can range from a mild difficulty in identifying colors to a total inability to perceive certain colors, such as red and green. Proper diagnosis and specific treatment are only performed by a specialist in ophthalmology.
Types of color vision deficiency
Color Vision Deficiency is caused by the absence or damage of the cells in the retina responsible for color perception. Thus, color vision deficiency can be classified according to how it appears or develops:
- Congenital or hereditary color vision deficiency, present from birth or genetically inherited. (Color blindness is a form of congenital color vision deficiency.)
- Acquired color vision deficiency, which can develop later in life and is usually a result of factors such as injuries, medical conditions, or other causes.
In turn, congenital color vision deficiencies can be classified according to how the colors that the patient can perceive are affected. Congenital color vision deficiencies can be:
- Achromatic, a case where vision is limited to a single color dimension;
- Dichromatic, a case where the patient has only two types of visual pigments in the cones;
- Trichromatic, the most common case of color vision deficiency, where all three basic colors (red, green, and blue) are present, but there may be problems distinguishing them.
Dichromatic color vision deficiencies can lead to protanopia (patients cannot see the color red), deuteranopia (patients cannot distinguish the color green), or tritanopia (the rarest case, where patients cannot see the color blue). In the case of dichromatic color vision deficiencies, red may be perceived as green, green may seem gray or red, and blue can be seen as green or gray.
Trichromatic color vision deficiencies are of three types: protanomaly (deficiency in perceiving red-green spectrum colors), deuteranomaly (deficiency in perceiving green color), and tritanomaly (deficiency in perceiving blue-green spectrum colors).
Total color vision deficiency is characterized by a complete lack of cone functionality. Patients cannot perceive certain basic colors and distinguish only shades of black and gray. This can be genetically inherited or occur as a result of a stroke.
How does dyschromatopsia occur?
The retina, the inner layer of the eye, plays a crucial role in transmitting visual information to the brain. In the retina of the eye, there are two main types of photosensitive cells: cone cells and rod cells.
Cone cells are responsible for color perception. They contain special visual pigments that react to different wavelengths of light. This is why a variety of colors can be perceived. In a poorly lit environment or at night, the cones do not function, and color perception is reduced or nonexistent. In this case, vision relies on rod cells that perceive light and shadow contrasts, but do not distinguish colors.
Patients with normal vision have three different types of cones:
- L cones for the color red, which react to long wavelengths;
- M cones for the color green, which react to medium wavelengths;
- S cones for blue color, which react to short wavelengths.
These types of cones and the wavelengths they react to define the range of the spectrum of shades and colors that a patient can see. Each color is the result of the stimulation of different types of cones depending on the wavelength of the light that reaches the retina.
When one of these types of cones does not function correctly or is missing, color perception is affected. For example, in the case of protanopia, the absence of L cones causes the patient to have difficulty in perceiving the color red.
Causes of color vision deficiency
The causes of color vision deficiency can be genetic or caused by other factors.
Hereditary color vision deficiency can be caused by a change in the X chromosome and can be passed from mother to newborn, even in cases where the father suffers from this disorder.
Among the most common factors influencing the occurrence of color vision deficiency are:
- Macular degeneration , which occurs with aging affecting directly vision and colors;
- Certain infections or exposures to toxic substances;
- Optic nerve atrophy
Color vision deficiencies caused by external factors are usually asymmetrical. These can also be accompanied by other eye disorders and usually affect the red-green and blue-yellow axes.
Color vision deficiencies caused by hereditary factors usually affect both eyes and are symmetrical. In these cases, the eye functions are not affected, and the perception of colors does not worsen over time. Patients with hereditary color vision deficiencies generally have difficulties in distinguishing shades of red and green.
Diagnosis and treatment
In diagnosing color vision deficiency, the following color perception tests are generally used:
Ishihara Test
This test uses pseudoisochromatic plates that contain colored dots, grouped with pigments of varying intensity. On these plates, numbers are marked which healthy patients can distinguish, but patients with color vision deficiency cannot differentiate. The Ishihara Test is useful for the early diagnosis of color vision deficiency, but does not provide detailed information about the severity of the condition.
Farnsworth Test
This test consists of colored circular shapes that must be arranged in the correct order based on color and shade. It is considered the most sensitive test for classifying and measuring the severity of color vision deficiency. Patients are evaluated based on how accurately they can arrange these colored shapes in the correct order.
Nagel’s Anomaloscope
This device allows the patient to mix red and green lights to obtain a certain shade of yellow (sodium yellow), which helps in the accurate diagnosis of the specific type of color vision deficiency. Nagel’s Anomaloscope is useful for evaluating and quantifying color perception deficiencies.
The ophthalmologist can diagnose the specific type of color vision deficiency and can customize treatment or solutions for the needs of each patient.
The treatment of inherited color vision deficiency is generally limited and focuses on improving color perception. Although there is no specific treatment that can completely cure color vision deficiency, the doctor may prescribe wearing special glasses or contact lenses. These medical devices can adjust colors so that they are easier to perceive and identify. If the color vision deficiency was acquired due to a condition such as cataract, the treatment will primarily target this underlying condition.
This article provides general information about color vision deficiency. For the proper detection of this disorder and other vision conditions, a medical examination is necessary for a diagnosis and appropriate treatment.
Bibliography:
- www.barraquer.com, https://www.barraquer.com/en/pathology/dyschromatopsia, accessed on January 5, 2024;
- www.espaillatcabral.com, https://www.espaillatcabral.com/en/blog/item/que-es-la-discromatopsia, accessed on January 5, 2024;
- icrcat.com, https://icrcat.com/en/anomalous-colour-vision/, accessed on January 5, 2024;
- eyewiki.org, https://eyewiki.org/Color_Vision, accessed on January 5, 2024.
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