Which physical examination finding is indicative of conjunctivitis?

Conjunctival injection, characterized by redness of the conjunctiva, is a primary indicator of conjunctivitis. This condition involves inflammation of the conjunctival membrane that lines the eyelid and covers the white part of the eyeball. The redness occurs due to increased blood flow to the vessels in the conjunctiva as a response to inflammation. This sign is often accompanied by other symptoms, such as discharge, itchiness, or tearing, depending on whether the conjunctivitis is viral, bacterial, or allergic in origin.

In contrast, pupil dilation is not a characteristic finding associated with conjunctivitis, as it might signify other ocular issues such as trauma or neurological problems. Corneal opacity often indicates more severe conditions affecting the cornea itself, such as infections, dystrophies, or scarring, rather than conjunctivitis. A drop in visual acuity could occur in various eye conditions, but it is not a direct hallmark of conjunctivitis, which typically preserves vision unless complications arise. Thus, conjunctival injection remains the most definitive examination finding indicative of conjunctivitis.