The main difference between conjunctivitis and keratitis is the difference in the site of onset, one is an inflammation that occurs on the surface of the conjunctiva and the other is an inflammation that occurs on the surface of the cornea. In addition, the clinical manifestations are different. Conjunctivitis and keratitis are common eye diseases in ophthalmology. The common underlying causes are mainly infectious factors. Among the infectious factors are common bacterial infections, viral infections, fungal infections, etc. Rarely, there are infections such as mycoplasma and chlamydia. Of course, there are also some non-infectious physical factors, such as chemical irritation, sand and dust irritation and so on. Other inflammatory diseases of the conjunctiva and cornea are caused by immune factors or secondary to systemic diseases. The main difference between conjunctivitis and keratitis is that, in addition to the difference in the site of onset, there are also differences in clinical symptoms. Keratitis is often characterized by photophobia and foreign body sensation, while conjunctivitis is mainly characterized by congestion of the conjunctiva, increased ocular discharge, and less photophobia and foreign body sensation. The difference between conjunctivitis and keratitis is relatively simple and can be seen under a slit lamp microscope. In clinical practice we must be strict in distinguishing between conjunctival and keratoconjunctival inflammation. It is important to determine exactly which factor is causing the inflammation. Because of the different causes, the treatment will be different. Of course, the medication will also be different.