Corneal fistula is one of the complications of keratitis. It is not a fistula, but rather a loose tissue embedded in a corneal perforation from which atrial fluid exudes through the fissure. Corneal fistulas are most likely to occur in patients whose pupillary rim is embedded in the area of the corneal perforation. The main signs are a dark black bulge on the corneal surface, loss of the anterior chamber, and softening of the eye. Sometimes the corneal perforation does not heal completely and a corneal fistula is formed. A small, dark black bulge appears in the center of the white spot at the site of the rupture, while the anterior chamber disappears and the eye becomes soft. The eye immediately compensates by increasing atrial aqueous production in order to maintain the normal hardness of the eye. If this bulge is closed by the new membrane, the increased atrial aqueous production will gradually increase the intraocular pressure and cause secondary glaucoma. If the pressure continues to rise, the symptoms of an acute glaucoma attack can be caused, and the membrane breaks through, the symptoms disappear, and the eye becomes soft again. However, soon after the fistula is closed again by the new membrane, and the IOP increases again. Eventually, endophthalmitis, full-blown septicemia, or intraocular hemorrhage occurs due to fierce bacterial infection, and the eye eventually atrophies. It also ends because of long-term softening of the eye, flattening of the cornea, clouding of the lens, and even retinal detachment. The examination and diagnosis methods of corneal fistula: 1, oblique illumination method and oblique illumination with magnification method The oblique illumination method is to hold a spotlight torch in the right hand to illuminate the examined eye from the side of the patient, while the thumb and forefinger of the left hand separate the upper and lower eyelids in order to examine the conjunctiva, cornea, anterior chamber, iris, crystal, etc. The thumb and index finger of the left hand hold a magnifying glass about 10 times larger, the middle finger gently pulls the upper lid, and the ring finger can pull down on the lower lid to open the lid fissure. The examiner’s eye is placed close to the magnifying glass and the distance between the magnifying glass and the examined eye is adjusted so that the area to be examined, such as corneal foreign bodies, vascular opacities and posterior corneal sediment, can be clearly seen.