UMD Neuroscientist Calls for Clearer Nomenclature in Photoreceptor Research
A new paper co-authored by Biology’s Juan Angueyra aims to tackle a century-old communication problem by making it easier to identify visual systems in vertebrate species.
University of Maryland neuroscientist Juan Angueyra believes his field of research has a “communication issue.” Scientists do not describe the diversity of photoreceptors—light-sensitive neuronal cells in the eye that enable vision—in the same way across vertebrate species.
Some researchers refer to photoreceptors, which include rods and cones, by the colors of light they are most sensitive to (e.g., blue, green and red), while others refer to them by their wavelength sensitivity (e.g., short, medium, long and sometimes ultraviolet). Further complicating matters, researchers discovered that some species possess more photoreceptor subtypes than others, and the names of these subtypes vary among species.
“It’s confusing to everyone,” said Angueyra, an assistant professor in UMD’s Department of Biology who holds a joint appointment in UMD’s Brain and Behavior Institute. “Whenever you're trying to make arguments across species, you have to explain to everybody what exactly you are referring to.”
In a new paper published on May 7, 2025, in the journal PLOS Biology, Angueyra and his co-authors call for a standardized method of naming rods and cones across vertebrate species based on their shared evolutionary history.
Much of the earliest photoreceptor research, conducted over a century ago, focused on humans before mice became the most widely used animal model for vision. Even between these two species, the naming convention for cones and rods is confusing—and the problem only compounds when considering a larger diversity of animals, Angueyra explained.
“When you look at all the species beyond those two, the nomenclature completely falls apart,” Angueyra said.
Because the language was created to describe human photoreceptors, things quickly get complicated when studying animals such as birds, which have two extra cone subtypes. In their paper, Angueyra and his co-authors argue for a broader approach that accounts for the shared evolutionary history of vertebrates. This approach involves looking back even further to account for photoreceptor subtypes that existed long before humans entered the picture.
“Pre-vertebrates—ancient organisms before the emergence of vertebrates—already had four cone subtypes and rods, and a lot of species like fishes and reptiles kept that diversity of photoreceptors,” Angueyra explained. “But in the dinosaur era, when mammals went to the forest and became nocturnal, they lost photoreceptor subtypes. When we focus all our understanding of the visual system on mammals, we're studying a visual system that lost some properties.”
For the new nomenclature, the research team proposes using a numbered system to describe cones that descended from one of the four ancestral cone types. Codes containing other relevant information—the wavelength of maximal sensitivity or the specific type of protein expressed in a photoreceptor cell, for instance—can be added in subscript text, enabling more specificity if needed.
Angueyra said this system, spearheaded by the paper’s lead author Tom Baden, a neuroscience researcher at the University of Sussex, will also make it easier to account for any new photoreceptor types that are discovered in the future. This may be especially likely for chickens, which have been the subject of recent groundbreaking photoreceptor research, according to Angueyra.
Although there is no formal process for changing this nomenclature, Angueyra hopes other researchers in his field will adapt their proposed system. Throughout his career, Angueyra has studied vision in primates, squirrels and marine animals, and he believes a unified nomenclature could enable interspecies comparisons of visual systems—an understudied research area.
“Understanding how the eye is built across species is definitely useful to know, and the more species we study, the more puzzle pieces we get,” Angueyra said. “And what we learn from all these species is always useful to understand our own system [in humans] because, in a way, we're all linked through our history.”
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The paper, “ A standardized nomenclature for the rods and cones of the vertebrate retina,” was published in PLOS Biology on May 7, 2025.
