Very small, round vesicles containing fluid and cellular debris observed on the surface of the cornea under slit-lamp examination in some types of corneal dystrophy and in wearers of extended wear contact lenses, due to chronic hypoxia. They appear to originate in the basal layer of the corneal epithelium as a result of cellular necrosis. They can be seen by slit-lamp examination using a magnification of at least ✕20. If caused by extended wear contact lenses, the patient should be advised to change to daily wear contact lenses of high oxygen transmissibility. Syn. microepithelial cysts.