The black eye is smaller, usually due to the following reasons: 1, caused by true microphthalmos, a congenital developmental abnormality, usually with a genetic predisposition, means that the diameter of the eye is less than 20mm, at this time the diameter of the cornea will also shrink in equal proportion to the shrinking diameter of the eye, resulting in the black eye looks smaller, usually patients will be accompanied by complications such as high hyperopia. 2, caused by small corneas, belonging to congenital developmental The diameter of the cornea will shrink, usually less than 10mm, and it will easily be accompanied by complications such as glaucoma. 3, caused by the ring of old age, usually the size of the black eye is normal when the patient is young, but as the patient grows older, lipid deposition occurs at the corneal limbus, resulting in the peripheral cornea becoming white, thus making the black eye smaller.