Using fMRI, new vision study finds promising model for restoring cone function

In the retinas of human eyes, the cones are light-sensing photoreceptor cells responsible for color vision, daylight vision, and the perception of small details. Both humans and dogs are affected by inherited retinal diseases that damage cones, making dogs an excellent model for studying these diseases. “Canine models are useful for studying retinal diseases because they have a variety of different naturally occurring genetic disorders. The ultimate goal is to first demonstrate that these disorders can be treated in canines before translating it to human patients,” says Huseyin O. Taskin, the first author of a paper published in Translational Vision Science & Technology.

To determine if an experimental treatment, such as gene or cell therapy, is successful in dogs, researchers must be able to assess their level of visual function before and after the treatment. Current methods of assessing visual brain function in dogs can require weeks if not months of dog training and are invasive. Therefore, vision scientists at the University of Pennsylvania School of Veterinary Medicine assessed whether functional magnetic resonance imaging (fMRI), a noninvasive technique that shows which areas of the brain are most active based on blood flow, could be used to study cone vision. They looked at brain responses to lights that stimulate only the cone cells in dogs with three different kinds of naturally occurring retinal disease and in dogs with normal vision.

The researchers found that fMRI can detect brain responses to daylight vision for black and white information as well as color information, and it can identify the area of the visual cortex that responds to stimulation of a region in the dog retina that is rich in cones and similar to the fovea, a part of the human retina responsible for sharp central vision. They also found they can use fMRI to measure the relative degree of loss of daylight vision. Mutation of a gene called NPH5 causes a disease in dogs in which cones are present but not functional. When the researchers supplied a healthy copy of NPH5 with gene augmentation therapy, they found that the response in the brain to black and white stimulation was restored. That makes this disease a promising one in which to study whether photoreceptor cell replacement—where scientists introduce new cones into the retinas of dogs— would be a successful approach for restoring cone vision in the future.

Source: University of Pennsylvania, ScienceDaily, January 26, 2024; see source article