Aging-related ptosis and dermatochalasis: This is the most likely diagnosis given the patient's symptoms of ptosis (drooping eyelids) and dermatochalasis (excess skin in the upper eyelids), which are common findings in the aging population. Weight loss can exacerbate the appearance of these conditions due to the loss of facial fat.

Involutional ptosis: This condition is characterized by the drooping of the eyelid due to the weakening of the muscles that lift the eyelid, often seen in older adults. It can be bilateral and may be more noticeable after weight loss.
Blepharochalasis: A condition involving the eyelids, characterized by recurrent episodes of eyelid edema (swelling) followed by the development of redundant, lax skin. While less common, it could be considered in the differential, especially if the patient reports episodes of swelling.

Myasthenia gravis: An autoimmune disorder that can cause muscle weakness, including the muscles controlling eye movements. Ptosis can be a presenting symptom, and it is crucial to consider this diagnosis due to its potential for significant morbidity if left untreated.
Third cranial nerve palsy: This condition can cause ptosis, among other symptoms like double vision. It is essential to rule out because it can be a sign of an underlying serious condition, such as an aneurysm or stroke.

Chronic progressive external ophthalmoplegia (CPEO): A rare mitochondrial disorder that affects the external eye muscles, leading to ptosis and limited eye movements. It is a rare condition but should be considered in patients with progressive ptosis and external ophthalmoplegia.
Horner syndrome: Characterized by ptosis, miosis (pupil constriction), and anhidrosis (lack of sweating), this syndrome can result from disruption of the sympathetic nerves supplying the eye. It is less likely but important to diagnose due to its association with potential underlying serious conditions.