A painful lesion on the eyelid margin is most likely diagnosed as?

A painful lesion on the eyelid margin is most likely diagnosed as a stye, also known as a hordeolum. This condition occurs when there is an acute infection in the oil glands of the eyelid, typically caused by bacterial pathogens. The infection leads to localized redness, swelling, tenderness, and a prominent painful lesion on the eyelid margin.

Being at the margin of the eyelid and characterized by pain and swelling distinguishes a stye from other conditions. A chalazion, for instance, is a cyst that can develop on the eyelid, but it is generally not painful and occurs due to the obstruction of an oil gland. Anisocoria refers to unequal pupil sizes and is unrelated to the presence of lesions on the eyelid, and drusen are small yellowish deposits that can form on the retina and typically do not present with lesions on the eyelid margin or pain.