In this blog post, we will look at how the main cells of the retina, such as rod cells and cone cells, convert light into electrical signals and transmit them to the brain via the optic nerve.
The retina plays an important role in our ability to distinguish objects and perceive the world around us. The retina is a neural tissue that receives light entering through the pupil, forms images, and converts the light stimuli into electrical signals that are transmitted to the brain for recognition. Therefore, if the retina does not function properly, it is difficult to perceive objects correctly, even if there is sufficient light.
The retina consists of photoreceptors, bipolar cells, and ganglion cells. Among these, photoreceptors convert light stimuli into electrical signals. Photoreceptors are rod cells and cone cells, which perform different roles depending on the brightness of light.
Rod cells are distributed around the periphery of the retina and mainly detect weak light in dark places with less than 0.1 lux. Rod cells contain a photoreceptive pigment called rhodopsin, which is highly sensitive to light, enabling us to distinguish the contrast and shape of objects even in the dark. Rhodopsin is formed when retinene binds to a protein called opsin in dark places, and when light enters, it is immediately broken down into opsin and retinene. The photochemical reaction that occurs at this time generates an electrical signal, which is transmitted to the brain through the optic nerve. Rhodopsin is produced from vitamin A, and in bright places it cannot bind to opsin, but in dark places it binds to opsin and becomes rhodopsin. The repeated synthesis and decomposition of rhodopsin enables us to see objects even in the dark. Decomposed rhodopsin is removed from the retina, so a lack of vitamin A prevents the smooth production of new rhodopsin, leading to night blindness.
Cone cells are mainly distributed in the center of the retina. Although they are not very sensitive to light, they have three types of photopigments called red, green, and blue, which selectively respond to the visible light wavelengths of red, green, and blue, and play a role in distinguishing colors in bright places with a brightness of 0.1 lux or more. Although the photopigments differ, the photochemical reactions of cone cells are similar to those of rod cells. An abnormality in one of the photopigments of cone cells causes color blindness.
When moving from a dark place to a bright place, the retina’s sensitivity remains fixed at the level of the dark place, causing momentary glare. This is because the large amount of photoreceptive pigments in the rod cells and cone cells are immediately broken down by the strong light stimulus. At this time, the bipolar cells suppress the function of the rod cells and activate the function of the cone cells, regulating the cone cells to respond appropriately to the brightness of the light within about one minute. Conversely, when entering a dark place, the function of the cone cells is inhibited by the bipolar cells, and the function of the rod cells is activated, causing the rod cells to actively synthesize rhodopsin, which increases the sensitivity of the retina, allowing it to respond appropriately to the brightness of light within 20 to 30 minutes. The reason for the difference in response time between the two is that rhodopsin takes longer to synthesize than other photoreceptive pigments.
Through this process, ganglion cells transmit electrical signals from photoreceptors to bipolar cells, which are then transmitted to the optic nerve, ultimately connecting the visual center of the brain so that it can recognize light. Thanks to the intricate structure and function of the retina, we are able to clearly recognize objects in various environments. Understanding the function of the retina also plays an important role in treating and preventing visual impairments.
In modern medicine, various research and technological developments are being conducted for the treatment and prevention of retinal diseases. For example, technologies such as gene therapy to prevent retinal degeneration and artificial retinas to restore vision are gradually advancing. These cutting-edge technologies offer hope that more people will be able to regain their vision in the future.
In addition, it is also important to make efforts to maintain retinal health in our daily lives. You can maintain retinal health by getting regular eye exams, eating foods rich in vitamin A, and resting your eyes frequently. A healthy retina plays an important role in helping us see the world more clearly and vividly.
Therefore, it is necessary to understand the importance and function of the retina and to make continuous efforts to maintain retinal health. These efforts will greatly help improve our quality of life and provide a better visual experience.
