Potatoes contain two kinds of glycoalkaloids, both natural toxins, called solanine and chaconine, and while the whole potato contains these glycoalkaloids, the concentration is highest in the eyes, green skin and sprouts that form.

Source: https://kidotalkradio.com/ixp/659/p/idaho-potato-poisoning/

“Seeing green on potatoes indicates the formation of the toxin solanine, also found in the sprouts,” she said.

Source: https://www.huffingtonpost.co.uk/entry/is-it-safe-to-eat-a-potato-thats-turning-green-or-sprouting-eyes_uk_65435ec5e4b06bc01e22f73f