Iris cysts are hollow cavities in the eye filled with secretion. They come in various sizes, numbers, shapes, pigments and can be free-floating, attached to the pupillary margin or within the posterior chamber. Most frequently iris cysts don't cause any issues, but they can cause problems like: “fly biting” behavior, corneal endothelial pigment, lens capsular pigmentation, altered iris movement, decreased aqueous outflow with subsequent glaucoma or block the vision when grown too big. They can be acquired or innate. Possible causes are inflammation, drug-induced, uveitis, a trauma, tumor-induced, parasitic or implantation. Most frequently iris cysts are benign and need no treatment. Sometimes iris cysts are causing problems and need to be deflated. Iris cysts can be treated with trans corneal diode laser treatment, fine-needle aspiration or surgical excision. For the treatment of iris cysts is a conservative approach favored. Introduction Mackenzie diagnosed the first iris cyst in 1830, which was a posttraumatic iris cyst in the anterior chamber. Because of the wide variety of iris cysts, a categorization was needed. This categorization was proposed by Shields in 1981 and was based on 2 main groups: primary and secondary cyst. Primary cysts origin is neuroepithelial, and rarely causes any issue. Primary cysts can be subcategorized based on their location in the eye. However, secondary cysts can cause problems like decreased vision, secondary glaucoma, uveitis or corneal edema and origin from implantation, metastasis, miotics or parasites. Secondary cysts are further categorized based on their origin. Brief overview of the anatomy of the iris The iris is a thin circular structure in the eye which consists of two layers, on top is the stroma and underneath the pigmented epithelial cells. It separates the eye in the anterior and posterior chamber, is responsible for the eye's color, and its function is to regulate the size of the pupil. By controlling the size of the pupil it regulates the amount of light reaching the retina. Depending on the amount of light, the iris opens with high intensity light and closes with low intensity light. The iris is able to control the size of the pupil due to radial and circular muscles which attach to the stroma. The circular muscle, sphincter muscle, contracts in a circular motion, making the pupil smaller, but by contracting the radial muscles, dilator muscles, the pupil enlarges. Primary cyst The classification of primary cysts is according to the categorization of Shields.