Gout crystals. Polarised light micrograph of uric acid crystals in the synovial fluid (a lubricating liquid in joints) from a patient with gout. Uric acid is a waste compound that is produced during the digestion of purine-rich foods such as meat and fish. It is normally excreted in urine, but a diet high in purine-rich food causes high uric acid blood levels. Gout is a condition in which the uric acid crystallises inside joints. It is an extremely painful condition, which leads to swelling of the joint and intense pain on moving or even lightly touching the affected joint. Treatment is with anti-inflammatory drugs and painkillers. Magnification: x570 when printed 10 centimetres wide.