University Researchers Discover New Neural Pathway in Eyes That Supports Vision

Biologists at Johns Hopkins discovered a type of retina cell that is critical for vision. While working with laboratory mice, the researchers found a photoreceptor in the retina that detects contrast between light and dark.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are a type of neuron in the retina of the mammalian eye. Now, the JHU researchers have discovered that the ipRGCs express melanopsin, which is a type of photopigment that undergoes a chemical change when it absorbs light. This allowed them to determine how that type of photoreceptor can detect differences between light and dark.

The melanopsin signaling occurred in the presence of rods and cones, which are the most well-known photoreceptors in the retina. There are about 120 million rods in the human eye and between 6 and 7 million cones. Rods are highly sensitive to light and are activated in dim or low-light environments and cones drive vision in brighter conditions and are crucial for color detection.

"Rods and cones were thought to mediate vision and ipRGCs were thought to mediate these simple light-detecting functions that happen outside of conscious perception," said postdoctoral fellow Tiffany M. Schmidt in this JHU news release. "But our experiments revealed that ipRGCs influence a greater diversity of behaviors than was previously known and actually contribute to an important aspect of image-forming vision, namely contrast detection."

The ipRGCs were originally thought to exclusively detect light for non-image-dependent functions, but in the experiment with mice, the researchers found that those with melanopsin present in their ipRGCs more effectively saw contract in the Y-shaped maze they were placed in.

The Johns Hopkins University study, "A Role for Melanopsin in Alpha Retinal Ganglion Cells and Contrast Detection," was published in the journal Neuron on Wednesday.