Cystine is a semi-essential amino acid, the most important of the 3 amino acids (glycine, glutamate, cystine), that are required by the body for the production of glutathione. Cystine deposits are accumulations of crystalline cystine in the sclera and cornea. Seen above located toward the palpebral conjunctiva, they resemble little grains of rock salt or snow flakes in the sclera. This occurs at a cellular level when the body is not sufficiently breaking down and transporting cysteine out of the lyosomes, causing impaired cellular energy metabolism. Cystine deposits can often be associated with active thyroid disorders, blindness and renal failure.
In a chronic circumstance, the cysteine deposits can become so large that they scratch the interior underside of the eyelid causing irritation, and sometimes calluses. If you can imagine the cystine deposits as tiny, very sharp crystals, you can understand how painful they can become. Correct diet and incorporation of a good quality digestive enzyme can aid in reducing and dissolving these deposits.