pigment-, pigmento- +

(Latin: "paint"; coloring matter involving both animals and plants)

This unit is directly related to the pict- family of words.

pigmentum nigrum
The black pigment of the lamina vitrea (transparent inner layer) of the choroid (middle layer between the retina and the sclera, or the tough white outer coat) of the eyes.
progressive pigmentary dermatosis
A chronic skin disorder resulting from hemorrhages into the skin, chiefly on the legs of young men, and characterized by purple patches that spread and turn brown.
respiratory pigment
1. Any of the oxygen-carrying substances in the blood and tissues, such as hemoglobin and myoglobin.
2. Any of various colored conjugated proteins; such as, hemoglobin, that occur in living organisms and function in oxygen transfer in cellular respiration.
retinitis pigmentosa (RP)
Any one of a large group of inherited disorders in which abnormalities of the photoreceptors (the rods and cones) in the retina lead to progressive visual loss.

People with retinitis pigmentosa first experience defective dark adaptation ("night blindness"), then constriction of the visual field ("tunnel vision") and eventually loss of central vision.

Having no pigmentation or without any pigmentation.
xeroderma pigmentosum (XP)
A genetic disease characterized by such extraordinary sensitivity to sunlight that it results in the development of skin cancer at a very early age.

Children with xeroderma pigmentosum can only play outdoors safely after nightfall. They have been called "midnight children", the "children of the dark", the "children of the night", and "vampire children".

Anyone with xeroderma pigmentosum develops severe sunburn and eye irritation within minutes of exposure to sunlight.

Other signs of XP include the development of ultradry skin (the word "xeroderma" means extreme dryness of the skin) plus blisters, heavy freckling, and dark spots on the skin (the word "pigmentosum" refers to these pigmented areas of the skin).