Described herein is an IOP control device for implantation in an eye of a patient, comprising a drainage tube, a pressure-driven flow system, and a flow rate measurement system. The drainage tube includes a drainage lumen in fluid communication with an anterior chamber of the eye. The flow system is in fluid communication with the drainage lumen, and is configured to control the flow of fluid through the drainage tube. The flow rate measurement system is disposed distal to the flow system, and comprises a flow tube including a known hydraulic resistance to flow, a proximal pressure sensor disposed at the proximal end of the flow tube, and a distal pressure sensor disposed at the distal end of the flow tube. The flow tube includes a proximal end, a distal end, and a lumen extending therebetween that is configured to be in fluid communication with the drainage lumen.
