Hidrocystoma on the eye of a 60 year old female patient. Hidrocystomas, also known as Moll's gland cysts, are rare, benign cysts that tend to form in the apocrine sweat glands. They usually occur on the head and neck, commonly affecting the eyelids, as apocrine glands are more concentrated in these regions. They present as small, smooth, semi-transparent dome-shaped nodules filled with a watery fluid. They grow slowly and can range from flesh-coloured to blue-black. Hidrocystomas are more common in adults over 60 years old and both sexes are equally affected. The exact cause of this disorder is unknown but it is thought to be due to a blockage of the gland. They are typically asymptomatic and disappear on their own, although the appearance may cause discomfort. The most common treatment is surgical removal. Alternative treatments such as cauterisation (burning) and laser removal are also available.