Allergic Reaction: The swelling occurred in the morning and improved with steroid cream, suggesting an allergic reaction. The rapid response to steroid cream further supports this diagnosis, as allergic reactions often respond well to topical corticosteroids.

Contact Dermatitis: This could be due to an irritant or allergen that came into contact with the eyelid, causing inflammation and swelling. The application of steroid cream would help reduce the inflammation.
Angioedema: Although less common, angioedema could cause sudden swelling of the eyelid. However, it typically involves deeper tissues and may not respond as quickly to topical steroids.
Blepharitis: An inflammation of the eyelids that can cause swelling, especially in the morning due to accumulated debris. It might not fully explain the rapid improvement with steroid cream unless it was an allergic component.

Orbital Cellulitis: An infection of the tissues surrounding the eye, which is a medical emergency. Although the improvement with steroid cream makes this less likely, any signs of infection (e.g., increased redness, warmth, purulent discharge, vision changes) should prompt immediate investigation and treatment.
Basal Cell Carcinoma or Other Malignancies: While unlikely given the acute presentation and response to treatment, any new, unexplained swelling, especially in older adults, warrants consideration of malignancy. A biopsy might be necessary if the swelling does not fully resolve or recurs.

Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause a wide range of symptoms, including swelling of the eyelids. It would be an unusual presentation and not likely given the response to steroid cream.
Sarcoidosis: Another autoimmune disease that can affect any part of the body, including the eyes. Eyelid swelling could be a manifestation, but it's rare and would typically be part of a broader systemic illness.