Central serous retinopathy (CSR): a condition in which fluid builds up beneath the retina of the eye, leading to distorted vision. The retina is the tissue lining the back of the eye that sends vision signals through the optic nerve to the brain. In central serous retinopathy, the fluid is thought to leak from the choroid, a tissue layer under the retina that contains blood vessels. When the cells that protect the retina from fluid from the choroid become defective, fluid builds up beneath the retina, similar to a blister in the skin. The disruption in the retina causes distorted vision. The exact cause of the defects is not well understood. CSR typically affects only one eye, but it is possible for both eyes to be affected. Central serous retinopathy is sometimes referred to as central serous choroidopathy.