Light enters the eye and travels through the lens to the back of the eye, where light-sensitive cells such as cones and rods send signals to the brain.
A new lens has been added to the process. The powerhouse of the cell, the mitochondria, appears to be acting like little "microlenses" to help deliver light to the nerve cells.
Senior author, National Eye Institute neurologist, Wei Li, said, "We were surprised by this fascinating phenomenon that mitochondria appear to have a dual purpose."
Mitochondria are very small. Most of the chemical energy required is generated by the cells so they can perform their functions. The kind of structure that would be very effective at redirecting light doesn't seem to be what they look like from biology class.
A simplified structure of achondrion.
The researchers were surprised that the mitochondria are in the light-sensitive outer segment of the cones. This means that light can hit the mitochondria directly, which could cause light to scatter off in weird directions, or even stop light from reaching nerve cells altogether.
The National Eye Institute scientist John Ball wrote about how the complex, lipid-rich organelles are poised to affect light passage into the outer segment.
We show that despite the risk of light scattering or absorption, these tightly packed mitochondria focus the light for entry into the outer segment.
The thirteen-lined ground squirrel was used as a model organisms by the researchers. The animals have lots of cones to detect color, but not as many as other mammals, so they can't see as much in darkness. Researchers were able to look at an isolated layer of cones.
The squirrel had to be euthanized and their eyes were removed and placed on a microscope slide.
The researchers were able to shine light into the photoreceptors with the mitochondria still alive.
We can't confirm yet that this is happening in human cells, but more research will have to be done. It also explains an unknown about the mammal's retina.
The function of mitochondria may explain the phenomenon known as the Stiles-Crawford effect.
The Stiles-Crawford effect is a property of cone receptors where light that enters the center of the pupil produces more of a response in our cone cells than light that enters closer to the edge.
The team used computer models to show that the Mitochondrial interaction with light matched the effects of the Stiles-Crawford effect.
The team wrote that the feature of cone mitochondria that delivers light with anangular dependence akin to the Stiles-Crawford effect provides a simple explanation for this essential visual phenomenon that improves resolution.
It looks like the powerhouse of the cell has been helping us with our vision.
The paper has been published.
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