Color Blindness
Introduction
Despite technological advances, ongoing scientific investigations, improvements in health care, and new research techniques, causes and nature of genetic mutations remain understudied. “Genetic disorders comprise a vast galaxy of anomalous conditions and exert an extraordinary impact on the human population” (Wynbrandt & Ludman, 2008, p. iv). Color blindness is generally identified as one of congenital diseases though researchers distinguish other causes of this visual disorder (Krapp, 2002; Golden & Peterson, 2010; Wong, 2011; Montgomery, 2012).
Color blindness, daltonism, color vision defects, and color vision deficiency are terms used to define humans’ absent or diminished abilities to perceive and/or to distinguish various wavelengths of light (Wynbrandt & Ludman, 2008; Genetics Home Reference, 2006). John Dalton, an English scientist, who suffered from color blindness, first discovered and described his visual defects in his publication "Extraordinary facts relating to the vision of colours” in the 18th century.
Background
Although all patients with color blindness experience difficulties in seeing colors, their brightness, and shades, the clinical picture, severity, and manifestations of color vision deficiency vary depending on the pathophysiological mechanisms of the disease and conditions of the retina. The retina is a sensory layer of an external wall of eyes, “the interior surface of the back of the eyeball” (Wynbrandt & Ludman, 2008, p. 94). The retina contains wavelength receptors called rods and cones. Due to specific functions of rods and cones, people are able to perceive light and recognise colours and their shades.
Types of Color Blindness
A type of color vision deficiency depends on its causative aspect; thus, color blindness can be either inherited or acquired (Krapp, 2002; Golden & Peterson, 2010; Wong, 2011; Kohl et al., 2012; MedlinePlus, 2012; Montgomery, 2012). Color vision deficiency of hereditary nature is specific to both eyes of a patient while, being acquired, the disorder can afflict only cone cells of a single eye. Moreover, the severity of symptoms can vary in different eyes. The inherited pathologies of color vision generally occur at the birth and they do not change at all over time. The acquired color blindness can change or be aggravated throughout a long time owing to processes of ageing and comorbid illnesses. In accordance with findings of research on color vision deficiency, such diseases as diabetes, leukemia, Alzheimer’s disease, glaucoma, retinitis pigmentosa, retinal degeneration, liver diseases, chronic alcoholism, macular degeneration, multiple sclerosis, sickle cell anemia, Parkinson’s disease, and brain traumas can cause this disorder. Moreover, color vision defects can be triggered by industrial toxins and such medications as barbiturates, hydroxychloroquine (Plaquenil), some antibiotics, etc. (Krapp, 2002; MedlinePlus, 2012).
Types of Cones
Cone cells are photoreceptors, which are responsible for high-acuity color vision (Marieb, 2012; MedlinePlus, 2012). “Photoreceptors are considered neurons, but they also resemble tall epithelial cells turned upside down, with their “tips” immersed in the pigmented layer (Marieb, 2012, p. 492). Depending on their sensitivity to colours, cone cells contain light-sensitive pigments and provide humans with abilities to perceive light and recognise red, green, and blue colours (Wynbrandt & Ludman, 2008; Rizzo, 2010; Marieb, 2012). Combinations …