Which condition is described as being highly contagious?

Conjunctivitis, often referred to as pink eye, is well-known for its highly contagious nature, especially when caused by viral or bacterial infections. This condition can spread easily from person to person through direct contact with infected individuals or contaminated surfaces. The pathogens responsible for conjunctivitis can be transmitted via hand-to-eye contact or through respiratory droplets.

In contrast, the other conditions listed are not typically classified as contagious. Dacryocystitis, an infection of the tear drainage system, primarily affects individuals and does not transmit between people. Blepharitis, an inflammation of the eyelids, is often linked to skin conditions or bacterial growth but is not contagious. Astigmatism is a refractive error caused by the shape of the cornea or lens, and it has no infectious component, meaning it cannot be spread to others. Therefore, conjunctivitis is clearly distinguished as the highly contagious condition among the options provided.