From the above website (I'm not advocating that it's right just this is the claim):
> What can cause a contrast sensitivity deficit?
> Many things can affect the ability to perceive contrast. These include nutritional deficiencies, the consumption of alcohol, drug/medication use, and exposure to endogenous or exogenous neurotoxins and/or biotoxins, including volatile organic compounds (VOCs), venom from animal or insect stings or bites, some species of mold and the mycotoxins and microbial VOCs they produce, cyanobacteria, dinoflagellates (particularly Pfiesteria and Ciguatera), apicomplexans, parasites, heavy metals like mercury and lead, and the pathogens responsible for Lyme disease and its common co-infections. For more information, see our Research resources.
> What can cause a contrast sensitivity deficit? > Many things can affect the ability to perceive contrast. These include nutritional deficiencies, the consumption of alcohol, drug/medication use, and exposure to endogenous or exogenous neurotoxins and/or biotoxins, including volatile organic compounds (VOCs), venom from animal or insect stings or bites, some species of mold and the mycotoxins and microbial VOCs they produce, cyanobacteria, dinoflagellates (particularly Pfiesteria and Ciguatera), apicomplexans, parasites, heavy metals like mercury and lead, and the pathogens responsible for Lyme disease and its common co-infections. For more information, see our Research resources.