The eye is a cool organ. Our eyes allow us to move about our world and make sense of all that we see. In fact, many in the medical and scientific community view the eye as the front of the brain. (No pun intended.) That leads to two questions:
1) If the eye lens sustained an injury, how would it heal, since the lens doesn’t have blood vessels and immune cells travel via blood vessels.
2) When it comes to genetic blindness, what is going on in the genes that is leading to blindness?
Research is taking place to answer those two questions.
At Thomas Jefferson University in Philadelphia, research on the eye lens found out something surprising. The reason for the eye lens not having blood vessels is that they would obscure vision. Since there aren’t any blood vessels, the belief was that immune cells couldn’t get to this part of the body.
“Why would we evolve a tissue that is so central to our being able to see without ways to ensure its protection, its ability to repair itself?” says Sue Menko, PhD, Professor in the Department of Pathology, Anatomy and Cell Biology at Thomas Jefferson University, who led the research. She wanted to find out if the eye starts an immune response after an injury. Previous research showed that when the lens is ailing, immune cells aren’t just going to the lens, they also appear in the cornea, retina, and vitreous body. These are parts of the eye that don’t have immune cells at the ready.
Her research suggested that the immune cells come from the ciliary body, the muscle that helps the lens to focus and that’s where her team looked. Manko’s lab used fluorescent markers and high-powered microscopes to observe mouse eyes a day after receiving a scratch on the cornea. The imaging analysis showed that after the injury, the immune system starts a response to protect the lens. Immune cells head to the lens by way of the ciliary zonules, which are ligaments that connect the eye to the ciliary body. They then move along the surface of the lens to protect the cornea from adverse effects as a result of the injury. In addition, some of the cells crossed the lens capsule, in order to keep the lens under the right amount of tension.
What about the genetic basis of blindness? There is a gene called cystathionine beta-synthase “a” (cbsa) that is responsible for homocystinuria in humans. This is a disease that causes defective vision, hemorrhaging, stroke, heart attacks and premature death. Yet, there is a species of fish known as the Mexican cavefish that has this gene and they thrive, in spite of both having this gene and not having eyes. Since these fish live in darkness, they don’t need eyes. So, what do the Mexican cavefish have that humans don’t and how can this lead to treatments for homocystinuria.
William Jeffery, PhD, a professor of biology at the University of Maryland studied this fish to find out what makes it able to live with this genetic abnormality. Jeffery’s lab along with collaborators from the National Institutes of Health and Stanford University studied these genes in certain regions and looked for a change in expression during a part of the Mexican cavefish’s development when eye degeneration happens.
The researchers identified four genes and the cbsa gene was mutated in all the of the varieties of the Mexican cavefish. The cbsa gene prevented blood flow to the eyes during a critical part of the fish’s embryonic development. This leads to the fish having underdeveloped eyes that are covered by skin. The researchers then reversed eye degeneration by injecting normal cbsa genetic material into cavefish embryos and they developed functioning eyes.
This study showed that knowing how the mutations influence eye degeneration can lead to a better understating of the gene’s function in the vascular system and lead to treatments for homocystinuria.
Again, the eyes demonstrate that there is more to them than meets the eye.