Introduction

Visual processing begins with the conversion of light to an electrical signal in retinal photoreceptors. In this review we describe the current state of knowledge of this conversion process. First we summarize the remarkable performance of rod and cone photoreceptors and briefly describe their salient anatomical features. Then we present a brief overview of the transduction process before delving into the details. We divide transduction into activation and inactivation phases because there is a clear distinction between the molecular processes underlying the onset and recovery phases of the light response. Finally, we consider how the balance between activation and inactivation is achieved, and how these processes contribute to photoreceptor adaptation.