<unk> , a<unk>  vision deficiency, is the inability to perceive differences between some of the<unk> s that others can distinguish.
There are different classifications of<unk> .  It can be classified by cause or by clinical appearance.
By cause:
Acquired
Inherited:
Monochromacy - Also known as "total<unk> "
Rod monochromacy (achromatopsia) - The condition of having only rods in the retina.  A rod monochromat will be unable to see well in normal daylight levels of illumination.
Cone monochromacy - A rare total<unk>  that is accompanied by relatively normal vision, electoretinogram, and electrooculogram.
Dichromacy - A moderately severe<unk>  vision defect in which one of the three basic<unk>  mechanisms is absent or not functioning.  It occurs when one of the cone pigments is missing and<unk>  is reduced to two dimensions.
Protanopia - A severe type of<unk>  vision deficiency caused by the complete absence of red retinal photoreceptors.
Deuteranopia - A<unk>  vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination.
Tritanopia - A very rare<unk>  vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors.
Anomalous trichromacy - A common type of inherited<unk>  vision deficiency, occurring when one of the three cone pigments is altered in its spectral sensitivity. This results in an impairment, rather than loss, of trichromacy (normal three-dimensional<unk>  vision).
Protanomaly - A mild<unk>  vision defect that results in poor red-green hue discrimination
Deuteranomaly - By far the most common type of<unk>  vision deficiency, mildly affecting red-green hue discrimination
Deuteranomaly - A rare, hereditary<unk>  vision deficiency affecting blue-yellow hue discrimination; unlike most other forms, is not sex-linked
Monochromacy - Also known as "total<unk> "
Rod monochromacy (achromatopsia) - The condition of having only rods in the retina.  A rod monochromat will be unable to see well in normal daylight levels of illumination.
Cone monochromacy - A rare total<unk>  that is accompanied by relatively normal vision, electoretinogram, and electrooculogram.
Dichromacy - A moderately severe<unk>  vision defect in which one of the three basic<unk>  mechanisms is absent or not functioning.  It occurs when one of the cone pigments is missing and<unk>  is reduced to two dimensions.
Protanopia - A severe type of<unk>  vision deficiency caused by the complete absence of red retinal photoreceptors.
Deuteranopia - A<unk>  vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination.
Tritanopia - A very rare<unk>  vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors.
Anomalous trichromacy - A common type of inherited<unk>  vision deficiency, occurring when one of the three cone pigments is altered in its spectral sensitivity. This results in an impairment, rather than loss, of trichromacy (normal three-dimensional<unk>  vision).
Protanomaly - A mild<unk>  vision defect that results in poor red-green hue discrimination
Deuteranomaly - By far the most common type of<unk>  vision deficiency, mildly affecting red-green hue discrimination
Deuteranomaly - A rare, hereditary<unk>  vision deficiency affecting blue-yellow hue discrimination; unlike most other forms, is not sex-linked
Rod monochromacy (achromatopsia) - The condition of having only rods in the retina.  A rod monochromat will be unable to see well in normal daylight levels of illumination.
Cone monochromacy - A rare total<unk>  that is accompanied by relatively normal vision, electoretinogram, and electrooculogram.
Protanopia - A severe type of<unk>  vision deficiency caused by the complete absence of red retinal photoreceptors.
Deuteranopia - A<unk>  vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination.
Tritanopia - A very rare<unk>  vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors.
Protanomaly - A mild<unk>  vision defect that results in poor red-green hue discrimination
Deuteranomaly - By far the most common type of<unk>  vision deficiency, mildly affecting red-green hue discrimination
Deuteranomaly - A rare, hereditary<unk>  vision deficiency affecting blue-yellow hue discrimination; unlike most other forms, is not sex-linked
By clinical appearance:
Total<unk> 
Partial<unk> 
Red-green
Dichromacy (protanopia and deuteranopia)
Anomalous trichromacy (protanomaly and deuteranomaly)
Blue-yellow
Dichromacy (tritanopia)
Anomalous trichromacy (tritanomaly)
Color blindness
Snow blindness
Myopia
Cortical blindness
Amblyopia
Red eye  
Red eye
Red eye 