A chalazion is a firm round lump, or cyst on the inside of the upper or lower eyelid. This is usually caused by a chronic inflammation or blockage in the Meibomian gland. The Meibomian gland produces an oily film over tears to prevent them from evaporating, therefore keeping the eye moist. When a blockage occurs, a small sac of fluid forms.
This can grow to the size of a pea. Due to its location, it can be mistaken for a stye. Chalazions can cause discomfort, swelling, tenderness and inflammation of the eyelid. If large, chalazions can also affect vision. A chalazion will sometimes get better on its own and unless infected they are completely harmless.
However, if it is large, uncomfortable, affects your vision or doesn’t respond to other treatments, your ophthalmologist may suggest a surgical procedure to remove it.