Among their functions, horizontal cells are believed to be responsible for increasing contrast via lateral inhibition and adapting both to bright and dim light conditions.

[1][2] They are thought to be important for the antagonistic center-surround property of the receptive fields of many types of retinal ganglion cells.

Depending on the species, there are typically one or two classes of horizontal cells, with a third type sometimes proposed.

Mosaic arrangements provide a mechanism to distribute each cell type evenly across the retina, ensuring that all parts of the visual field have access to a full set of processing elements.

The moderately wide lateral spread and coupling of horizontal cells by gap junctions, measures the average level of illumination falling upon a region of the retinal surface, which horizontal cells then subtract a proportionate value from the output of photoreceptors to hold the signal input to the inner retinal circuitry within its operating range.

[4][7][8] Two mechanisms that are not mutually exclusive likely contribute to horizontal cell inhibition of glutamate release by cones.

Both postulated mechanisms depend on the protected environment provided by the invaginating synapses that horizontal cells make onto cones.

[4][10][11] The second postulated mechanism is relatively slow with a time constant of about 200 ms and depends on ATP release via Pannexin 1 channels located on horizontal cell dendrites invaginating the cone synaptic terminal.