Which of the following is NOT hereditary?

Conjunctivitis, also known as pink eye, is primarily an inflammation or infection of the conjunctiva, which is the membrane that lines the eyelid and covers the white part of the eyeball. It can be caused by a variety of factors including viral or bacterial infections, allergies, irritants, and environmental factors, rather than being passed down genetically. While certain conditions can have a hereditary component, conjunctivitis itself is not inherited in a direct genetic manner.

In contrast, migraines, diabetes, and nystagmus can have hereditary components. Migraines may run in families, with certain genetic factors potentially contributing to a higher susceptibility. Diabetes, particularly Type 2, has well-documented genetic and environmental interactions, meaning family history can significantly increase the risk of developing the disease. Nystagmus, which involves involuntary eye movements, can also have genetic links and may be associated with other hereditary conditions. Thus, when considering the question of what is NOT hereditary, conjunctivitis stands out clearly due to its primarily environmental and infectious causes.