The patient’s left eyelid is swollen and the right eye is not swollen, which may be related to eye trauma, mosquito bites, blepharitis and other reasons. 1. Eye trauma: If the patient’s left eye is hit by eye trauma, it can lead to bruising and swelling of the eye, and the right eye is not involved without similar symptoms. 2. Mosquito bites: If a patient’s left eye is bitten by a mosquito, the acid in the mosquito saliva can cause an allergic reaction in the patient’s left eyelid, resulting in swelling of the left eyelid and normalization of the right eye. 3. Blepharitis: If the patient’s left eye gland is infected by bacteria or other germs, blepharitis may occur, and the patient’s eyelid may become congested, swollen, painful and other discomforts, while the right eyelid is not involved, then there are no discomforts. It is recommended that patients with significant swelling in one eye should seek prompt medical attention to assess their condition and standardize treatment under the guidance of a physician.