How we see things, how we distinguish colors, and how we make vivid, colorful memories might seem to be a puzzle. Our vision is much more evolved than any camera and is an essential tool for us to survive in this world. However, diabetic eye problems tend to rob us of this vital sense, slowly but steadily.
High blood sugar levels and high blood pressure over a period of time create structural changes in the cells of the eye leading to gradual vision loss. Lack of oxygen supply, microaneurysms, diabetic macular edema, retinal tear, and retinal detachment are some of the events that create vision loss.
To shed more light on how diabetes damages eyesight, we have to first understand how our eyes function.
Our vision is all about light. We see the world around us in wavelengths of red, blue, and green and our eyes work more or less like cameras. To facilitate vision, different parts of the eye work in tandem.
Incoming light and its intensity is controlled by the muscles of the iris. They contract and relax to change the size of the pupil. When the incoming light fluctuates, the size of the pupil also changes. When the light is brighter the pupil contracts, and when it is dim, the pupils dilate. This is called pupillary light response. After crossing a thin film of tears, light enters the cornea (a protective layer). Here the light is focused. This focusing is done as the cornea bends and refracts the light through the pupil.
Light passes through the aqueous humor, the pupil, and the vitreous humor and then reaches the retina where it is sharply focused. The retina itself contains millions of light sensitive receptors in the form of rods and cones. These light sensitive receptors called the rods and cones allow us to see in the dark and in the daytime.
When light hits the light sensitive receptors (the rods and cones), light is then converted into electrical impulses. These electrical impulses are then transmitted to the brain via the optic nerve. In the brain, the electrical impulses are interpreted to construct a version of space and reality.
To facilitate easy flow of electrical impulses to the brain via the optic nerve, the light sensitive receptors trigger a cascade of signals after light hits them. The signals move from the optic nerve of both the eyes to a point known as the optic chiasm. This is a crossing where optic nerves of both eyes partially cross. This crossing (the optic chiasm) allows the visual cortex to receive information from the same visual field of the same hemisphere. By processing information from both visual fields, the visual cortex generates binocular vision.
Signals from the optic chiasm enter the thalamus where information regarding color and detail are sent to the visual cortex. From here, the reconstruction of a coherent world with all its detail happens.
Vision is peripheral and central. Peripheral vision allows us to see objects and movement in the sides. Peripheral vision is facilitated by the rods (light sensitive receptors). Rods are also responsible for low light vision and vision in the dark. Central vision on the other hand is the process of seeing objects straight ahead. It allows us to make key judgments involving speed, and details of a path.
When it comes to discerning colors, shades, and hues of objects, we reconstruct all colors with wavelengths of red, blue, and green. The light sensitive receptors called cones are responsible for us to distinguish colors. They are present in an area in the retina called the fovea centralis.
Cones respond to red, green, and blue colors due to the presence of photo pigments. Depending upon the number of cones activated, and the intensity of the signal when we see a colorful object, our brains process the signal and creates a colorful world. In fact, our memory of color of an object might also influence our perception of color.
How Diabetes Changes Eyesight
People often get themselves tested for diabetes only after they experience blurry vision. This is a common diabetic eye problem. High blood sugar levels over a period of time damage the lens of the eye. In most cases, the lens of the eyes tend to swell. This swelling generally subsides only after taking medication and normalizing blood sugar levels.
In other cases, diabetic eye problems can manifest in the form of damaged blood vessels. It causes vision problems in the later stages as it develops into proliferative diabetic retinopathy. This can lead to vision loss.
In the next section, let us explore the intricate structure of the eye!