A chalazion is a cyst (a small sac of fluid) on the inside of the eyelid. Due to its location, it can be mistaken for a stye and can grow to the size of a pea. If a chalazion is large, it can cause discomfort or affect vision. It is caused by a blocked gland in your eyelid. The glands help to keep your eyes moist by preventing the watery layer on the surface of your eyes (tears) from evaporating. They do this by producing an oily film over the tears.
A chalazion will sometimes get better on its own. However, your ophthalmologist may suggest a surgical procedure to remove it if it is large, uncomfortable, affects your vision or doesn’t respond to other treatments.