Mitochondrial metabolism is a critical mechanism that is deregulated in numerous retinal diseases. Here, we elaborate a protocol to quantify oxygen consumption rate as a measure of mitochondrial respiration directly from mouse retinal tissue pieces. Our procedure combines the use of Seahorse extracellular flux technology and ex vivo retinal tissue isolation and is robustly reproducible under different treatment conditions. This protocol allows direct assessment of mitochondrial function in response to drug treatments or genetic manipulation in mouse models.