Which of the following conditions is not hereditary?

Conjunctivitis is considered to be primarily non-hereditary because it is most often caused by environmental factors, infections, or allergens. This condition, commonly known as pink eye, can arise from viral or bacterial infections, allergic reactions, or irritants such as smoke or pollution. While certain predispositions to allergic reactions might run in families, the condition itself is not directly passed down through genetic inheritance.

In contrast, the other conditions listed have a stronger hereditary component. Asthenopia, often related to strain on the eyes from prolonged use or refractive errors, can show a familial pattern but is not inherited in the traditional genetic sense. Keratoconus is a progressive eye disease that has been shown to have a genetic basis, often running in families. Similarly, certain types of cataracts have hereditary links, with specific genetic mutations increasing the risk of developing cataracts at a younger age. Thus, when considering these conditions, conjunctivitis stands out as one that is largely influenced by external factors rather than genetics.