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In spite of being a small organ, the eyelids contain numerous histological elements that can be the origin of benign and malignant lesions.
The eyelids are composed of four layers: Skin and subcutaneous tissue, striated muscle (orbicularis oculi), tarsus, and conjunctiva.                                                                                                                                                          

Most frequent uveal tumors are “ocular melanoma,” “uveal melanoma,” or “choroidal melanoma” are often used interchangeably. The terms describe melanomas, which arise from the eye, and can occur in the iris, ciliary body and/or choroidal regions of the eye. Melanomas are cancers that arise from specific types of pigmented (colored) cells in the body. Melanomas of the eye are rare.

Orbital tumors can be benign or malignant and arise primarily within the orbit or secondarily from an adjacent source, such as the eyelid, paranasal sinus, or intracranial compartment. Orbital tumors can also be metastatic from distant sites.
Some types of orbital tumors usually cause proptosis and displacement of the globe in a direction opposite the tumor. Pain, diplopia, and vision loss may also be present. The diagnosis of orbital tumors is suspected based on the history, examination, and neuroimaging (CT, MRI, or both), but confirmation often ultimately requires a biopsy. Causes and treatment vary by age group.

The wall of the eye has 3 main layers. From outside to inside there is: the white sclera, a blood vessel layer called the uvea (choroid, ciliary body and iris) and an inner retinal layer. Further, the pigment producing cells, “melanocytes” are primarily found in the vascular uveal layer. It is those melanocytes that can turn into malignant melanoma. Therefore, when melanoma happens in the choroid, they are called “choroidal melanoma,” the most common primary intraocular malignancy in adults. That said, choroidal melanomas are rare with 5 to10 out of each million people diagnosed with a choroidal melanoma each year. Choroidal melanomas can spread to other parts of the body.