Our visual perception of the external world relies on neural activity across a hierarchy of visual cortical areas, communicating via complex feedforward-feedback pathways. While feedforward pathways have been a focus of study, the role of the feedback pathway has remained poorly understood. Here we have developed a novel viral vector combination allowing for selective optogenetic inactivation of feedback pathways in the non-human primate brain. We show that even the most fundamental response properties of visual neurons, such as the receptive field size, are regulated by feedback signals from other regions of the visual cortex. Depending on its activity regime, cortico-cortical feedback can regulate receptive field size and contextual modulation of visual responses or the overall response gain of neurons.