Aging or Senile Ptosis: This is the most common cause of eyelid ptosis in the elderly due to the weakening of the levator palpebrae superioris muscle or its tendon, leading to a gradual drooping of the eyelid.

Third Cranial Nerve (Oculomotor Nerve) Palsy: This can cause ptosis due to the nerve's control over several eye muscles, including the levator palpebrae superioris. It might be accompanied by other symptoms like diplopia or an outward and downward deviation of the eye.
Horner Syndrome: Characterized by mild ptosis, miosis, and anhidrosis, Horner syndrome can result from disruption of the sympathetic nerves supplying the eye. It can be caused by various conditions, including stroke, carotid artery disease, or a tumor.
Myasthenia Gravis: An autoimmune disease that can cause fluctuating muscle weakness, including the muscles controlling eye movement, leading to ptosis that worsens with fatigue.

Stroke or Cerebral Vasculitis: Although less common, a sudden onset of ptosis could be a sign of a stroke or cerebral vasculitis affecting the brain areas responsible for eye movement.
Orbital or Brain Tumors: Tumors in the orbit or brain can compress or invade nerves controlling eye movement, leading to ptosis. Early detection is crucial for treatment and prognosis.
Giant Cell Arteritis: This condition can cause sudden vision loss and ptosis if it involves the posterior ciliary arteries or the oculomotor nerve. Prompt diagnosis and treatment are essential to prevent blindness.

Congenital Ptosis: Although typically identified in childhood, some cases might not be diagnosed until later in life, especially if mild.
Chronic Progressive External Ophthalmoplegia (CPEO): A mitochondrial myopathy that leads to progressive weakness of the external eye muscles, including those responsible for eyelid movement, causing ptosis.
Oculopharyngeal Muscular Dystrophy: A rare genetic disorder characterized by progressive ptosis and swallowing difficulties, typically presenting in the fifth or sixth decade of life.