Swelling of the left eye may be caused by kidney disease, eye disease, heart disease, endocrine disease and other diseases. 1. Kidney disease: patients with kidney abnormalities, such as renal failure, nephritis, etc., may cause water retention, resulting in varying degrees of edema, preferably in the eyes, limbs, head, etc., the patient will also be accompanied by lumbar pain, generalized fatigue and other discomforts. 2. Eye diseases: patients with ocular inflammatory diseases such as conjunctivitis, keratitis, dacryocystitis, etc., under the stimulation of inflammation, patients may experience eyelid swelling, photophobia, tearing and other discomforts. 3. Heart disease: patients with cardiac insufficiency can also cause eye swelling, facial swelling, lower limb swelling, mainly due to the impact of venous blood reflux caused by the severe cases of dyspnea and other discomforts. 4. Endocrine diseases: patients with abnormal thyroid function, such as insufficient secretion of thyroid hormone, can also cause the body’s metabolic function to decline, which may cause mucous edema, resulting in the phenomenon of left eye swelling. It is recommended that patients with obvious eye swelling should seek prompt medical attention to assess their condition and follow the doctor’s instructions for treatment.