[Vision] The eye analyzes light, and then the brain creates a three-dimensional world. And it all starts with the retina, a transparent membrane hiding behind the eye. Here, light is converted into electrical signals and transmitted to the brain. The retina is covered with dense optical receptors made up of special nerve cells – called cones and rods – that evolved from the ancient light-sensitive cells in the human brain. The reason why they are called cones and rods is simple, because they are long like mallets. However, they are not stupid. Each eye contains roughly 120-125 million optic rods, and in dim conditions optic rods are the main attraction. The amount of optic cones is much less (each eye contains 6-7 million optic cones), and in a bright environment the optic cones become the main character. This light uptake and conversion is not as simple as “you sing, I play”. There are three types of cones in the retina, each responsible for the detection of a specific visible spectrum: red, green and blue. An almost infinite number of hues and color gradients can be deconstructed and broken down into these three colors. The three colors, red, green and blue, are also the primary colors used to create colorful images on computer screens. Compared to the “cones”, the “rods” are very lonely and have only one type, which explains “why is our ability to distinguish colors in dark environments diminished?” There is a color recognizer in the cone cells, which we call “photoreceptors”. Each photoreceptor is made up of a light-sensitive chemical we call “retinol,” which is derived from vitamin A. These retinoids sit comfortably on the protein shell of the photoprotein. Among the three primary color recognizers (red, green and blue), the retinoids are slightly different, which ensures that each recognizer can only absorb and recognize a particular wavelength of light. When light strikes retinol, the latter then changes its molecular form, which causes the encapsulated retin to change shape. This is a domino-like biological effect that eventually leads to the activation of the optic nerve. The light signal travels from the optic nerve to the thalamus and eventually to the occipital lobe. The occipital lobe is located at the very back of the brain, and it is here that the three-dimensional world as we see it is reconstructed. It is the retina that can first “touch” the external world. It has a retinal projection map in which cells are tightly packed together. It’s not just a map, but the cells are divided in their functions, some are responsible for capturing the movement of objects, some for detecting their depth, some for observing their form, and some for taking in color. The signals taken in from the eye require some very clever processing so that the brain can figure out what it really wants to see and what is just “sauce”? Let’s say a hunting man stops his car to observe a pride of lions. His eyes first catch the light reflected from the lions and the surrounding grass, and then the retina is stimulated to form a two-dimensional image pattern that is transmitted to the primary visual cortex. With the help of the temporal lobe, the brain begins to construct a three-dimensional image to distinguish and recognize the different details in this hunting scene. The visual signal changes over time and the movement of any detail in the picture can be detected, both in terms of speed and direction. This processed data is also working at the same speed, without our own awareness. By studying patients suffering from visual agnosia, clues were gradually gathered to figure out how the brain processes visual scenes. We found that the problem occurred in the brain and not in the eyes. There is a classic example of a husband mistaking his wife for a “hat”. In his monograph of the same name, neurologist Oliver Sacks describes the case as follows: “Dr. P. was a very good pianist and music teacher, but also a patient. He was unable to recognize the objects he saw with his own eyes. On one occasion Dr. P. tried to put his wife on his head because he mistook her for a hat.” Dr. P is just one of many. Other patients with visual agnosia are unable to correctly perceive the depth of objects, the words of others or the faces of others. In addition, this disorientation can affect other senses, such as the inability to recognize smells or sounds. Vision Restoration] Visual impairment or blindness is usually the result of damage to the visual transmission pathways – loss of clarity of vision due to fogging of the cornea or lens; degeneration of the cornea; trauma to the visual cortex (located at the back of the brain) or stroke, etc. However, as time progresses, advances in biology, engineering and technology are opening more and more windows for patients who are losing or have lost their sight. Stem cell research, in particular, offers a sustainable hope for a growing number of diseases, including, of course, visual impairment. Stem cells can differentiate towards any kind of cell and naturally in the direction that scientists expect. Let’s see what superhuman feats stem cells have to offer. The otherwise crystal clear cornea becomes blurry and opaque after suffering damage or disease. At this point, we can surgically remove the damaged cells from the surface of the cornea and then transplant a fresh layer of corneal cells. Since this layer of fresh corneal cells comes from the donor eye (i.e. someone else’s eye), there are some risks involved, even if it is effective, such as rejection reactions and the gradual degeneration of the cells over time. Corneal stem cell transplantation, on the other hand, circumvents both of these risks. These stem cells can naturally become part of the cornea. These stem cells also continue to provide fresh corneal cells to replace the aged ones as they age. To avoid rejection, these stem cells are usually taken from the patient’s own other healthy eye or from a close relative. However, sometimes neither of these options is available, so scientists are trying to develop other available resources. Once the stem cells are obtained, they are first incubated in the laboratory as a thin layer of cells (a monolayer arrangement), and then incubated into more robust multilayers. These cells are gradually grown structurally with the support of the culture matrix. Finally, these tissues are transplanted into the patient’s eye. Smart vision repair – what does it mean? In a simple analogy, scientists are like a glass cleaner who allows more light to enter the retina, the main stage of vision. To use another analogy, macular degeneration causes damage to the retina, and in order to repair vision, scientists have to bypass these damaged retinas, which is a very big technical challenge. The cells in the retina are a medium, between light and nerve cells. Nerve cells are responsible for transmitting visual signals to the brain. The conduction pathway is the optic nerve. Let’s go back and look at the promise that stem cells hold for us, an incredible promise. Japanese scientists have succeeded in incubating stem cells from mice into retinal cells, but that’s not even the highlight. The real success was that they incubated the stem cells into a real structure, a real structure that could develop into a retina. The future of stem cell transplantation for human visual repair, while bright, still has a long way to go. At the moment, what is coming into view is the “retinal implant. This is a neural prosthesis, called an extraretinal implant, that consists of three elements that work in concert to repair a type of vision. These three elements include a camera (which captures light), a video processor (which translates the ingested video signal and converts it into an electrical signal), and finally, the retinal implant itself. The user wears a separate external camera, usually embedded in a pair of glasses, that captures the surrounding environment in real time. This form of visual signal makes no sense to a person. Therefore, it is necessary to divert these signals into a video processor. Here, the video signal is reinterpreted into an electrical signal. Just as in normal human visual processing, light is converted into electrical signals, which are then transmitted to the visual cortex. The process of video signals being interpreted into electrical signals can now be transmitted wirelessly to a receiver. And this receiver is located in the eye. This receiver completes the final leg of the visual journey – the connection to the retinal implant. This retinal implant is composed of a series of tiny electrodes and is buried directly within the retina, in direct contact with the optic nerve cells. The implant electrodes transmit signals to the visual cortex, but the wearer cannot experience vision in a normal way. Instead, they can only see changes in light and dark. The wearer can only slowly learn how to interpret and give meaning. A team from the University of Tübingen in Germany tried to develop a smaller, more delicate retinal implant. This new device, buried under the retina, has 1,500 optical sensitizers that capture light entering the eye directly and convert it into electrical signals that are transmitted directly along the optic nerve. As a result, this new device does not require any external hardware at all. The results of the initial trials are exciting, and people wearing this new device can quickly gain the ability to see objects, to see shapes, and to describe objects, such as letters.