What condition is characterized by a permanent drooping of the upper eyelid?

Ptosis is characterized by a permanent drooping of the upper eyelid, which can affect one or both eyes. This condition often results from weakness or paralysis of the eyelid muscles, particularly the levator palpebrae superioris muscle responsible for lifting the eyelid. Various factors can contribute to ptosis, including age-related muscle weakening, neurological conditions, trauma, or congenital factors.

In contrast, coloboma refers to a defect in the structure of the eye that may result in a gap, usually related to the failure of the optic fissure to close during development. Astigmatism is a refractive error caused by an irregular curvature of the eye's cornea or lens, leading to blurred vision. Diplopia, or double vision, occurs when the eyes do not properly align or track together, resulting in seeing two images of a single object. Each of these conditions differs significantly in their characteristics and effects on vision, which is why ptosis stands out as the condition specifically associated with eyelid drooping.