Appropriate terminology in the nomenclature of the color vision deficiency

The colour vision deficiencies (CVDs) are visual disorders occuring in the absence or abnormal function of one or more cones. Although the term ‘’Color blindness’’ has been used to describe CVDs, it is actually a wrong term for nomenclature. It seems that ’’color vision deficiency sould be correct term for this disorder because color blindness means the absence of the ability to detect or distinguish any color. CVDs include various mild or heavy, and hereditary or acquired color vision deficids. In this review, we aimed to summarize the CVDs. Correspondence to: Burak Turgut, MD, Professor of Ophthalmology, Department of Ophthalmology, Faculty of Medicine, Yuksek Ihtisas University, 06520, Ankara, Turkey, Tel: +90 312 2803601; Fax: +90 3122803605; E-mail: burakturgut@yiu.edu.tr

Human retina has two types of photoreceptors including rods, which are responsible for vision in dark; and cones, which are responsible for vision in bright light and colour vision. There are three types of cones including the long-wavelength cones (L-cones, sensitive to red color) with peak sensitivity at 560 nm; the medium-wavelength cones (M-cones, sensitive to green color) with peak sensitivity at 530 nm; and the short-wavelength cones (S-cones, sensitive to blue color) with peak sensitivity at 430 nm. The photon absorptions in different levels by three different cones provide the brain to discriminate colour. People with normal color vision are known as normal trichromats, and normal colour perception is also known as trichromacy [1][2][3][4]. The colour vision deficiency (CVD) occurs in the absence or abnormal function of one or more cones [5][6][7].
Color blindness is a term which has been used to describe the CVDs. However, it is wrong nomenclature. Correct term should be ''color vision deficiency (CVD)''. Because, the term ''color blindness'' means the absence of the ability to detect or distinguish any color [5][6][7].
Daltonism is derived from the name of first scientist John Dalton (1766-1844) who recognized and published his and his brother's redgreen CVD in the first scientific paper [8].
Color vision deficiencies are mainly divided into two groups as hereditary and acquired CVDs. In Table 1, the main specifications of hereditary and acquired CVDs have been given.

Achromatopsia (a-absence+chroma-color+opsis-vision) (Complete color blindness, rod monochromacy, rod monochromatism):
A term which "color blindness" should be used to call for ''the cases with acromatopsia or achromatosis, real or true color blindness, which perceive all objects around in the color of the grey color and its various hues. The subjects with achromatopsia are typically totally color blind, and they have no ability to distinguish colors in the different wavelength. These subjects have only the rods, and the cone receptors are completely absent [1][2][3][4][5][6][7][8].
Anomalous trichromatism (anomalous trichromacy): A term describing color vision deficiency (protanomaly or deuteranomaly or tritanomaly) in some color due to the decreasing or increasing in sensitivity of one or more different types of color receptor despite to have all three functional cones. Anomalous trichromats recognize the colors in different intensity of each primary colour as compared with a normal trichromat [1][2][3][4][5][6][7][8][9][10].

Protanopia/Protanopic (red-blind):
The red sensitive cones (L-cones) are absent. Protanopia is usually an inherited CVD and exists in almost 1% of the males. It is a severe type of CVDs. The subjects with protanopia can only perceive light wavelengths between 400-650 nm but not over 700 nm. They can perceive pure reds as black, and can not distinguish purple colours from blues. Additionally, these subjects perceive orange-tinted reds as very dim yellows and all orange-yellowgreen as a similar yellow hue [1][2][3][4][5][6][7][8][9][10].
Deuteranomaly/Deuteranomalous: It describes defective or weak green-vision. Deuteranomaly is a less severe hereditary and sexlinked form of red-green CVD. This CVD mildly affecting red-green hue discrimination is seen in 5% of European males, and is due to an anomalous shift in the green-sensitive cones and characterized by the problems of discrimination different shades of the same colour in the red-yellow-green spectrum [1][2][3][4][5][6][7][8][9][10].
Hereditary CVD: The inherited color vision deficiency which is usually caused by X-linked recessive gene, which is passed from a mother to her son [7,9,10].

Acquired CVDs
Ocular disease related acquired CVD: Secondary color vision deficiency is related to damages of the optic nerve or retina because of various diseases and injuries [3,5,7,9]. This form of CVD has three types: Type 1 red-green acquired CVD have protan CVD characteristics. Progressive cone dystrophies and retinal pigment epithelium dystrophies are in this class [3,5,7,9].
Type 2 red-green acquired CVD have deutan CVD characteristics with greater reduction in short-wavelength sensitivity and a milder blue-yellow loss. Op tic neuri tis is included into this class [7,9].
Type 3 blue-yellow CVD characteristics (tritan CVD). It may be accompanied by a shift of maximum luminance sensitivity to Copyright: ©2017 Turgut B. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.