In central serous retinopathy (sometimes called central serous choroidopathy), fluid builds up under the retina and distorts vision. Fluid leakage is believed to come from a tissue layer with blood vessels under the retina, called the choroid. Another layer of cells called the retinal pigment epithelium (RPE) is responsible for preventing fluid from leaking from the choroid under the retina. When, for unknown reasons, tiny areas of the RPE become defective, fluid builds up and accumulates under the RPE, much as liquid in a blister collects under the skin. As a result, a small detachment forms under the retina, causing vision to become distorted.