a mosquito looking You go through a lattice of microscopic lenses. You turn your head back, fly swatter in hand, and stare at the vampire with your humble single-lens eye. But it turns out that you may see each other and the world in more ways than you think.

A study published last month scientific progress It was found that inside the mammalian eye, mitochondria, the organelles that power cells, may act as a second role as a microscopic lens, helping to focus light on photopigments that convert it into neural signals for the brain to interpret. The findings show striking similarities between mammalian eyes and the compound eyes of insects and other arthropods, suggesting that our own eyes have hidden optical complexity and that evolution has made a very ancient part of our cellular anatomy Found new uses.

The lens at the front of the eye focuses light from the environment onto a thin layer of tissue at the back called the retina. There, photoreceptor cells — the cones that color our world and the rods that help us navigate in low light — absorb light and convert it into neural signals that travel to the brain. But the photopigments are located at the very end of the photoreceptors, just behind the thick mitochondrial bundles. The strange location of this bundle turns mitochondria into seemingly unnecessary light-scattering obstacles.

Mitochondria are the “last barrier” to light particles, said Wei Li, a senior investigator at the National Eye Institute and the paper’s senior author. For years, vision scientists couldn’t understand this strange location of these organelles — after all, most cells have mitochondria clinging to their central organelle, the nucleus.

Some scientists have proposed that the beams may have evolved close to where the light signal is converted into a neural signal, an energy-demanding process in order to pump it out easily and deliver it quickly. But then research began to show that photoreceptors don’t need as many mitochondria for energy — instead, they may get more energy from a process called glycolysis, which occurs in the cell’s gelatinous cytoplasm middle.

Li and his team learned about the role of these mitochondrial tracts by analyzing the cone cells of the ground squirrel, a small mammal with amazing daytime vision but effectively night blindness because its photoreceptors are disproportionately large in cone cells. .

After computer simulations showed that mitochondrial bundles may have optical properties, Li and his team began experiments on real objects. They used thin samples of squirrel retinas, and they stripped most of the retinal cells apart from some cones, so they “ended up with just a bag of mitochondria” neatly packed inside the membrane, Li said.

Illuminating and looking closely at the sample under a special confocal microscope built by John Ball, a scientist in Li’s lab and lead author of the study, revealed a surprising result. Light that passes through the mitochondrial bundle appears as a bright, sharply focused beam. The researchers captured photos and videos of light entering the darkness through these microlenses, where photopigments wait in live animals.

Rather than an obstacle, the mitochondrial bundles play a key role in helping to deliver as much light as possible to the photoreceptors with minimal loss, Li said.

Using simulations, he and his colleagues confirmed that the lens effect is primarily caused by the mitochondrial bundle itself, rather than the membrane around it (although the membrane plays a role). A quirk of the ground squirrel’s natural history also helped them demonstrate that the shape of the mitochondrial bundle is critical to its ability to focus: During the months that a ground squirrel hibernates, its mitochondrial bundles become disordered and compressed. When the researchers simulated what happens when light travels through a hibernating ground squirrel’s mitochondrial bundle, they found that it didn’t concentrate the light as much as it did when it was elongated and highly ordered.