A corneal fistula is not a fistula, but rather a piece of loose tissue embedded in a corneal perforation, with aqueous seeping out of the fissure. Corneal fistulas are most likely to occur in patients whose pupil rim is embedded in the area of the corneal perforation. The aqueous humor often leaks out along the pupillary margin and is not easily repaired by the epithelial cells. The main signs of corneal fistula are a dark black bump on the corneal surface, loss of the anterior chamber, and softening of the eyeball. Fluorescent staining can be further proved. Sometimes corneal perforation after healing incomplete and formed corneal fistula. In the center of the white spot at the ulcer, a small, dark black bulge appears, while the anterior chamber disappears and the eyeball becomes soft. The eye immediately compensates by increasing aqueous production in order to maintain the normal rigidity of the eye. If this bulge is closed by the new membrane, the increased volume of aqueous humor will cause a gradual increase in intraocular pressure and secondary glaucoma. If the intraocular pressure continues to rise, it can cause an acute glaucomatous attack, which breaks through the membrane and the symptoms disappear and the eyeball becomes soft again. However, the fistula is soon closed again by the new membrane and the IOP increases again. This is repeated over and over again, and eventually, due to violent bacterial infection, endophthalmitis, total ocular sepsis, or intraocular hemorrhage occurs, and finally the eyeball atrophies. It may also end with prolonged softening of the eyeball, flattening of the cornea, clouding of the lens, or even retinal detachment.