Periorbital cellulitis: This is the most likely diagnosis given the presentation, as it is a common condition characterized by infection and inflammation of the tissues surrounding the eye, often caused by bacterial pathogens such as Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus influenzae.

Orbital cellulitis: While more severe than periorbital cellulitis, orbital cellulitis involves infection of the orbital tissues posterior to the orbital septum and can present with similar symptoms, including eyelid swelling, redness, and pain, but typically with more pronounced proptosis and vision changes.
Blepharitis: An inflammation of the eyelids that can cause redness, itching, and swelling, often associated with meibomian gland dysfunction or seborrheic dermatitis.
Conjunctivitis: Inflammation or infection of the outer membrane of the eyeball and the inner eyelid, which can cause redness, discharge, and irritation, but typically does not involve the deeper tissues around the eye.

Cavernous sinus thrombosis: A potentially life-threatening condition that can arise from the spread of infection from the facial area to the cavernous sinus, characterized by symptoms such as bilateral eye findings, cranial nerve palsies, and signs of increased intracranial pressure.
Meningitis: Infection of the meninges, the protective membranes covering the brain and spinal cord, which can be a complication of sinusitis or other facial infections spreading intracranially, presenting with fever, headache, stiff neck, and altered mental status.
Endophthalmitis: A severe inflammation of the interior of the eye, usually caused by infection, which can result from trauma, surgery, or bloodstream infection, and requires prompt treatment to preserve vision.

Erythema multiforme: An acute skin condition characterized by target lesions, which can involve the periorbital area and may be associated with systemic symptoms or underlying infections.
Angioedema: A rapid swelling of the dermis, subcutaneous tissue, mucosa, and submucosal tissues, which can affect the periorbital area and may be part of an allergic reaction or hereditary condition.
Wegener's granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause inflammation of the blood vessels and affect various parts of the body, including the eyes, sinuses, and respiratory tract.