Many complications of diabetes and eyes originate from high blood sugar levels. Diabetes that is not controlled is the prime reason for many conditions like diabetic cataract, diabetic macular edema, and diabetic retinopathy. Glaucoma and diabetes are also closely linked.
If you have diabetes, and/or high blood pressure, it is very important for you to understand your eye and its structure. This allows you to recognize symptoms earlier, and take action before a lot of damage is done.
Though the eyes are very small in size, they contain numerous parts that work together to facilitate vision. Vision is possible only if light enters the pupil and reaches the retina.
Parts of the eye:
The sclera is the white portion of the eye. It contains elastic fiber and collagen and is attached to the extraocular muscles. It contains many nerves and blood vessels.
There are six extraocular muscles and these help in the movement of the eye. The extraocular muscles assist the eye to move toward the target object which has to be seen in detail. This is because of the fact that the fovea allows for sharp vision, but is centrally located in the macula. The movement of the extraocular muscles is both voluntary and involuntary.
The conjunctiva is a thin membrane that covers and lines the inner eyelids and the sclera. It performs the function of keeping the inner surface of the eye moist. It protects the eye from dust, and foreign organisms that cause infection. The conjunctiva consists of the bulbar conjunctiva, the palpebral conjunctiva and fornix conjunctiva. While the bulbar conjunctiva covers the eyelids and the anterior sclera, the palpebral conjunctiva lines the eyelids, and the fornix conjunctiva is the junction between the bulbar and palpebral conjunctiva.
This is the colored part of the eye that regulates the amount of light that enters the eye. This is present in front of the lens. It assists in adjusting the size of the pupil as the intensity of light fluctuates. One can visualize the pupil as an aperture and the iris as a diaphragm. The iris contains pigmented fibrovascular stroma in the front and pigmented epithelial cells in the rear. The iris is connected to the pupil by a sphincter muscle that facilitates contraction and dilation. It is surrounded by the white sclera.
The central hole located in the middle of the iris is the pupil. It is an opening through which light passes into the lens of the eye. The pupil dilates or contracts depending upon the intensity of light and the muscle movement of iris muscles. The pupil appears black and it absorbs light. When the eye is exposed to low light, the pupil dilates, and when the eye is exposed to bright light, the pupil contracts.
Cornea of the eye is a transparent part that covers the pupil, iris, and the anterior chamber. This is present in front of the eyeball. The function of the cornea is to refract light that enters the eye on to the lens. The cornea contains numerous layers including corneal epithelium, Bowman’s layer, corneal stroma, Descemet’s membrane, and corneal endothelium. It has numerous nerve endings that make it sensitive to temperature, touch, and exposure to chemicals. The cornea contains one of the most sensitive tissues of the entire body with very high pain receptors.
The lens of the eye is a major component that refracts and focuses light on to the retina. It is a transparent crystalline lens that has a biconvex lens and is situated behind the pupil. The lens is present in the anterior segment of the eye. It is held in its place with the help of the suspensory ligaments. Behind the lens is the vitreous body which contains the aqueous humor. The flexible and curved nature of the lens allows it to be focused on different objects of different sizes. When the ciliary muscles contract, the focal distance is short and relaxing the ciliary muscles increases the focal distance.
These are located inside the ciliary body. Movement of these muscles result in the relaxation and contraction of the lens of the eye.
The ciliary body contains the ciliary muscles and connects the choroid to the iris.
The vascular layer between the sclera and the retina is called the choroid. It contains the connective tissues and provides oxygen to the outer layers of the retina. The choroid contains four layers, which contain blood vessels and capillaries.
The retina is the inner layer of the eye. It contains light sensitive cells called the rods and the cones. While the rods allow a person to see in low light and darkness, the cones allow for vision in bright light. After light passes through the pupil, and the lens, it reaches the retina where it hits the rods and cones. Here they are converted into electrical impulses and through the optic nerve they reach the visual centers of the brain to interpret the image. The retina contains multiple layers and is innerved to facilitate transmission to the brain. The retina is divided into temporal and nasal halves.
It is a yellow oval-shaped area that is present near the center of the retina and at the back of the eye. It is surrounded by fovea. Since it is yellow in color, it has the capacity to absorb excess amounts of ultraviolet and blue light. In this way, it acts as a sunblock. The macula facilitates sharp vision due to the presence of fovea inside the macula.
The fovea, also known as the fovea centralis, is present in the macula in the form of a small indentation in the center of the macula. The fovea has a high concentration of cones, which allows to see the details of an object when the vision is directed to it. It helps in providing sharp and accurate central vision.
The visible portion of the optic nerve during an eye examination is called the optic disc or the optic nerve head. The optic disc area is also known as the blind spot area as there are no rods or cones to react to light that enter the retina. The optic disc is also the place where the optic nerve begins. It is even the point of entry for many blood vessels that supply blood to the retina.
The optic nerve is the nerve that carries visual information from the retina of the eye to the brain. It is also called the cranial nerve II. It is a paired nerve that is part of the twelve cranial nerves. The optic nerve is enclosed deep in the brain. It passes through the eye socket, and through the optic canal, optic chiasm, and to the visual cortex. The major function of the optic nerve is to transmit visual information in the form of electrical signals so that all the aspects of vision are facilitated.