The orientation of an edge is a fundamental visual cue, which is represented by the signals that the retinal ganglion cells transmit to the brain. How does the neural circuitry of the retina extract this information? Using SyGCaMP to image the properties of synapses in the inner retina and iGluSnFR to image glutamate release, we measured how retinal ganglion cells (RGCs) in zebrafish integrate excitatory synaptic inputs from bipolar cells to produce an output in the optic tectum. Orientation-selectivity is first observed in the synaptic terminal of bipolar cells and ~48% of inputs to RGCs are orientation-selective, with the large majority tuned to the vertical. Orientation-selective bipolar cell synapses act as pattern detectors for their preferred orientation, being inhibited by orthogonal orientations. We show that inhibition from amacrine cells is required for orientation selectivity in bipolar cell synapse. We use iGluSnFR to image how bipolar cells are wired up to individual RGCs and show that some RGCs receive selective wiring of functional types while others receive diverse. We compare the excitatory inputs impinging on single RGCs with the output of the same cell allowing us to develop models to account for the transformations occurring in the RGCs. We show how 1) orientation selectivity becomes stronger in the output of RGCs, 2) Retinal ganglion cells rapidly adapt, allowing some RGCs to efficiently signal transitions between different orientations.