Researchers here propose an interesting approach to restoring vision in cases of age-related macular degeneration. They are using a gene therapy targeted at photoreceptor cells to provide these cells with the ability to be stimulated by near-infrared light. In tests in mice, this appears to function as intended, though it is always challenging to assess the quality of vision (as opposed to its presence or absence) in such experiments.
The main cause of blindness in industrialized countries is the degeneration of photoreceptors, including age-related macular degeneration and retinitis pigmentosa. During the progression of degenerative photoreceptor diseases, light-sensitive and light-insensitive photoreceptor regions in the retina coexist. For example, macular degeneration patients lose vision in the central portion of their retina but retain peripheral eyesight.
Scientists have now succeeded in developing a new therapeutic approach to restore light sensitivity in degenerating retina without negatively affecting remaining vision. They were inspired by species found in nature, such as bats and snakes, that can localize near-infrared light emitted by the bodies of their preys. This is done by using heat-sensitive ion channels which are able to detect the heat of the near-infrared light. This enables the bats and snakes to superimpose thermal and visual images in the brain and thus react to their environment with greater precision.
To equip retinal photoreceptors with near-infrared sensitivity, the researchers devised a three-component system. The first component contains engineered DNA that ensures that the gene coding for the heat-sensitive channel is only expressed in photoreceptors. The second component is a gold nanorod, a small particle, that efficiently absorbs near-infrared light. The third component is an antibody that ensures strong binding between the heat-sensitive channel expressed in photoreceptors and the gold nanorods that locally capture near-infrared light and locally release heat.
The researchers first tested their system in engineered mice with retinal degeneration, confirming that near-infrared light effectively excites photoreceptors and that this signal is transmitted to retinal ganglion cells, the latter representing the output of the retina towards higher visual centers in the brain. Next, they showed that stimulating the mouse eye with near-infrared light is also picked up by neurons in a brain area that is important for conscious vision, the primary visual cortex. They also designed a behavioral test in which untreated blind mice were not able to use near-infrared stimulation to learn a simple task whereas blind mice treated with the three-component system could perform the task related to near-infrared stimulus.