Eyes that are one large and one small can be caused by ptosis, atrophy of the eyeball, or a dominant lesion in the eye socket. Ptosis in one eye causes the upper eyelid of one eye to be unable to elevate to its normal position, which makes the lid fissure smaller and appears to result in inconsistent size of both eyes. An atrophy in one eye can cause the onset eye to become smaller, with a noticeable asymmetry in the appearance of both eyes. Common causes of eye atrophy include old retinal detachment. Intraorbital space-occupying lesions in one eye, such as inflammatory pseudotumor and hemangioma, may push the eyeball to protrude and cause asymmetry in the size of both eyes. Patients should visit the ophthalmology department of the hospital in time, and the doctor will diagnose the specific cause through detailed examination, and then only take targeted treatment to eliminate the symptoms.