innerretina

Inner retina refers to the portion of the retina that contains the neurons and synaptic circuits responsible for initial processing of visual information before it is transmitted to the brain. It comprises the nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL), and inner nuclear layer (INL). The inner retina begins at the vitreous boundary and extends to the outer plexiform layer (OPL), which marks the start of the outer retina. Neurons include retinal ganglion cells in the GCL with axons forming the NFL, and various interneurons in the INL such as bipolar and amacrine cells, with horizontal cells extending processes to the outer retina. The IPL is the main synaptic zone where bipolar and amacrine cells connect to ganglion cells, enabling complex processing of light signals, contrast, and motion before they are transmitted outward.

Although photoreceptors reside in the outer retina, their signals are relayed to the inner retina where significant processing occurs. The inner retina thus serves as a key site for signal integration, temporal processing, and modulation prior to transmission via the optic nerve. It is supplied by the central retinal artery and its intraretinal capillaries, collectively forming the inner retinal circulation. Metabolic demand and vascular integrity of the inner retina are essential for maintaining function, and disturbances can have clinical consequences beyond the outer photoreceptor layer.

Clinically, glaucoma is associated with selective loss of retinal ganglion cells and thinning of the NFL and GCL. Other conditions, such as diabetic retinopathy and retinal vascular occlusions, can involve inner retinal ischemia, contributing to vision loss.