BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: vision

Zebrafish: The Cure to Vision Loss?

Sight is one way in which we, along with many animals, interact with the world. Unfortunately, some people are unable to interact with the world in that same manner. Whether it is hereditary blindness or vision loss due to a neurodegenerative disease, vision loss and eye damage is difficult to fix, especially at a neurological level.

Neurons are present throughout the body and are connected via the nervous system. Their function is to transmit information to the brain and the rest of the body. They do this by signaling other cells by what is called neuronal firing. Individual nerve cells send electrical impulses to others allowing the message to reach other parts of the body. Simply put in the case of eyes and sight, the lens collect and bend the light and that information is sent through the optic nerve to the brain which then processes the information to produce an image. Therefore, if the neurons in the eye are damaged, that information cannot be collected and sent to the brain.

One such eye problem is Macular Degeneration which targets the macula. The macula is the central part of the retina that collects details images from the center of one’s field of vision. Damage to the macula results in a loss of central vision. Those who have it still retain their peripheral vision, but if the case is severe enough, they are deemed legally blind. As of now, there is no known cure.

However, Johns Hopkins Medicine researchers have been studying some animals’ ability to regrow neurons. Fish, along with other cold-blooded animals have the ability to repair eye neurons after injury, and for a long time it was thought that these genes were not present in mammals. According to Seth Blackshaw, professor of neuroscience at John Hopkins University, “[there is] the potential for regeneration is there in mammals, including humans, but some evolutionary pressure has turned it off” (ScienceDaily.com).

Blackshaw’s team has been studying the supportive cells in the back of the eye in zebrafish. These cells, known as the Müller glia, are able to repair the retina by growing neurons. Blackshaw’s team examined the retinal damage and repair of zebrafish, chickens, and mice. They found that while chicken and mice both have the capacity and gene pathways to generate neurons, the transcription factors were blocked so that the neurons don’t regenerate. Blackshaw suspects that the inability to regenerate neurons is due to the fact that animals that are more prone to disease in the brain, or other neurological tissue, may have lost this regenerative ability in order to protect other brain cells.

All of this is very exciting news and I think it is fascinating that studying cells from a fish could potentially help people who suffer from vision loss. I never would have thought that an animal that seems so different from us could help solve a problem that people have been dealing with for centuries. However, I think it is the fact that perhaps we aren’t so different from animals, at least on a biological level, that we are able to study them in order to better understand ourselves. For example, as Blackshaw and his team has discovered, we have those same gene pathways that allow zebrafish to regenerate neurons. And while ours don’t work the same way as of now, they are still present despite years and years of evolution. In the end, I think that the similarities we share with other animals is something to think about.

Put it all in focus

We’ve all had that moment where we squeeze our eyelids into tiny slits in hoping the blurry paper or board in front of us will clear up and wonder, Why am I making my eyes smaller to see better? That doesn’t seem to make sense! The key is to start thinking of your eyes like a camera, a camera with aperture. When we look at something, photons are passing through our corneas and blending light rays together, which then pass through the crystalline lens and vitreous on their way to the retina. The physical building blocks of the eye, rods and cones, turn photons into electromagnetic impulses that are sent to the brain to be interpreted.

So to get to the point, why do we squint? The truth is our lenses try to focus to the best of their ability but they are not entirely flexible. So blurriness is usually indicative of a lens malfunction, missing the target in the back of the retina. When you focus your eyes on something, there are massive amounts of competing light sources and surrounding stimuli in your peripheral vision which can cloud your eyes focus. Heres where the camera reference comes in: squinting your eyes is comparable to tightening the aperture of a camera, allowing less conflicting light to interfere with the image its focusing on. So in fact, squinting your eyes does not work because it is changing the shape of your lenses, but rather because it is allowing less competing stimuli to interfere with its true focus.
If vision is continually blurry, it may not be a simple malfunctioning of your lens but rather due to physical eye damage, in which case glasses might be a good investment. Maybe we should start to think of the aperture of our personal lives a little more as well, theoretically squinting to focus on important tasks and present moments rather than being distracted by the ever-present stimuli around us. Just a thought…
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