Scientists Identify New Retinal Cells in Eyes that Help in Vision

A type of retina cell has been identified by biologists at Johns Hopkins University (JHU) that plays an important role for vision than previously thought. The researchers while working in the laboratory with mice, found a photoreceptor in the retina of the mice that can detect the difference between light and dark.

JHU researchers have discovered that intrinsically photosensitive retinal ganglion cells (ipRGCs) – a type of neuron found in the mammalian eye retina, express melanopsin, a photopigment that undergoes chemical changes while absorbing light. This phenomenon helped them to determine the difference between light and dark.

The familiar photoreceptors in the retina - rods and cones - play an important role in the melanopsin signaling. Rods are quite sensitive to light and get activated in low-light or dim environments, while cones are better in brighter conditions and are important 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. 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," said Tiffany M. Schmidt, a postdoctoral fellow in the JHU news release.

Earlier, ipRGCs were thought to detect light for non-image-dependent functions, but the new experiment with mice showed that those with melanopsin present in their ipRGCs are more effective in determining the contrast between light and dark.

"Melanopsin signaling is essential for full contrast sensitivity in mouse visual functions. The ipRGCs and melanopsin determine the threshold for detecting edges in the visual scene, which means that visual functions that were thought to be solely mediated by rods and cones are now influenced by this system. The next step is to determine if melanopsin plays a similar role in the human retina for image-forming visual functions." said Samer Hattar, associate professor of biology in the university's Krieger School of Arts and Sciences.

The details of the findings have been published in the journal Neuron.