Giant Papillary Conjunctivitis (GPC): This condition is a common issue for contact lens wearers, characterized by an allergic reaction to the contact lenses themselves or to deposits on the lenses. It leads to inflammation of the conjunctiva under the upper eyelid, causing swelling, redness, and discomfort.

Contact Lens-Related Infection (e.g., bacterial keratitis): Infections can occur due to improper hygiene, contaminated lens care products, or trauma to the cornea. Symptoms include pain, redness, and vision changes, in addition to swelling.
Allergic Conjunctivitis: An allergic reaction to pollen, dust, or other allergens can cause unilateral or bilateral eye swelling, redness, and itching.
Blepharitis: Inflammation of the eyelids can cause swelling, redness, and discomfort, often associated with crusting around the eyelashes.

Endophthalmitis: A severe, vision-threatening infection within the eye that requires immediate medical attention. It can be caused by bacterial or fungal infections, often related to contact lens use or recent eye surgery.
Acute Angle-Closure Glaucoma: A medical emergency characterized by sudden increased intraocular pressure, leading to severe eye pain, redness, swelling, and vision loss.
Orbital Cellulitis: An infection of the tissues surrounding the eye, which can cause swelling, redness, and pain. It can lead to serious complications if not promptly treated.

Sjögren's Syndrome: An autoimmune disorder that can cause dry eyes and may lead to unilateral or bilateral eye swelling among other systemic symptoms.
Ocular Rosacea: A condition that can cause inflammation of the eyes, leading to swelling, redness, and discomfort, often associated with skin rosacea.
Thyroid Ophthalmopathy: A condition associated with thyroid disease, leading to swelling of the tissues around the eye, including the eyelids, and can cause bulging of the eyes (exophthalmos).