The human body consists of numerous unique organs. The eyes are of great importance from both a biological and a social point of view. They not only serve as one of the most important sensory organs, but are also used as a means of communication. Nevertheless, they are one of the most sensitive human organs. Even minor impacts can cause major damage to them.
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Leading Medicine Guide Editors
Article overview
The human eye
The human eyes are highly developed sensory organs that are characterized by an enormous sensitivity to light. As a result, they are mainly used to transmit light stimuli to the human brain. In this way, they enable people to better orient themselves in their environment.
The eyes perceive different colors and brightness values and can also see clearly at different distances thanks to the flexible eye lens.
Basically, human eyes belong to the group of lenticular eyes. As a result, they are very similar to those of many other vertebrates. With the exception of minor differences, the eyes of most vertebrates therefore have a similar structure.
The eyes are located in two adjacent bony cavities in the skull. These are technically known as orbits. In addition to the eyes, the orbitae also contain a thick layer of connective tissue, several fat pads and muscles. These serve to protect and influence the eyes. In addition, the eyelid shields the eye from external influences. The eyelid closure reflex ensures that the eyelids close immediately in the event of danger and protect the eyeball from the effects of foreign bodies.
The visible areas of the eye: sclera, iris, pupil and cornea (transparent)
Anatomy of the eye
The eye itself consists of several anatomical structures, each of which has its own function. This enables the complex functionality of this sensory organ. The eye mainly has the following three structures:
- Visual pathway
- appendages
- Eyeball
Eyeball
In specialist literature, the eyeball is referred to as the bulbus oculi. It is a spherical body that can rotate around any axis within fixed limits. However, its position within the eye socket always remains the same during this process.
The eyeball is surrounded by three different layers: the inner, middle and outer eye skin. The interior of the eye, on the other hand, consists of the lens and the eye chamber at the front of the eye and the vitreous body at the back.
Anatomy of the eye © bilderzwerg / Fotolia
The inner skin of the eye is more precisely called the retina. This structure contains all the light-sensing cells that are ultimately responsible for vision. These are divided into cones and rods. While the cones enable color vision, the rods are primarily responsible for recognizing gradations between black and white.
The middle part of the eye also consists of several structures. In medicine, a distinction is made between the choroid, the ciliary body and the iris. While the choroid supplies the retina lying on it with nutrients, the ciliary body primarily serves as a suspension for the lens of the eye. This projects the incident light onto the retina.
The iris acts as the pupil and regulates the incidence of light onto the lens. It is also known as the iris and is responsible for the color of the human eye.
The outer skin of the eye consists of the transparent cornea and the white sclera. The sclera covers the entire eyeball except for the front area. The transparent cornea, which serves as the windshield of the eye and protects the iris, sits in a circle at the front. It is constantly moistened with tear fluid by the lacrimal glands.
The appendage organs
All connected appendage organs are also considered part of the eye in medical terms. These include, among others
- the lacrimal apparatus
- the eye muscles
- the conjunctiva
- the eyelids
The lacrimal apparatus is responsible for the production of tear fluid. This not only moistens the cornea, but is also responsible for cleaning the eye.
The external eye muscles are also part of the appendage organs. Humans have a total of seven external eye muscles that enable the eyeball to move. Their aim is to direct the eyes towards an object in the shortest possible time.
The eyelids, on the other hand, mainly serve to protect the eyes. They consist of skin, muscles and a thin layer of connective tissue. In addition to shielding the eyes from external influences, they also serve to distribute tear fluid. In this way, they clean the cornea and keep it moist. The eyelashes on the upper and lower eyelids have an additional protective function for the eye and are primarily intended to catch very small particles.
The visual pathway
The visual pathway is the part of the eye that is responsible for transmitting signals to the brain. It mainly consists of the optic nerve, which connects to the retina. It has a length of 4.5 centimeters and is connected to the eyeball via the macula. Furthermore, the optic nerve comprises over one million bundled nerve fibers that extend from the sclera of the eye to the optic nerve junction.
How the eye works
Vision is the most complex of all six human senses. For comprehensive orientation, the light entering the eye must be converted into nerve impulses. The visual pathways transmit these to the brain, which processes the signals into visual impressions.
The following areas play a key role in vision:
- Cornea
- iris
- lens
- retina
The cornea is clear and slightly curved. It allows light to pass through and refracts it through its curvature before it reaches the lens of the eye.
The iris can contract and dilate. This enlarges or reduces the pupil in its center. The width of the pupil determines the amount of light that enters the eye.
The crystalline lens is located behind the iris. It is responsible for focusing the rays of light. This function has mainly been adopted by modern cameras. It is surrounded by muscles and fibers. These change the shape of the lens by pulling on it. In this way, the bundling of the light rays is manipulated to produce a sharp image.The retina is located at the back of the eyeball. With over 120 million sensory cells, it can convert the incoming rays of light into nerve signals. A distinction is made between rod-shaped and cone-shaped sensory cells. However, the density of both sensory cells varies on the retina. This is why the center, the so-called "yellow spot" (macula), has the highest concentration of sensory cells and represents the focus of human attention.
Ultimately, the information converted into nerve signals by the retina is transmitted to the brain via the optic nerve.
Common eye diseases and their causes
A total of over 100 different clinical pictures are known that can affect the human eye. These always lead to a reduction in the performance of the eye and thus restrict the patient's ability to see to varying degrees. In many cases, complete blindness occurs as the disease progresses. In the early stages, they usually result in a reduction in visual acuity or a restriction of the visual field. In addition, color vision disorders also occur in many cases. The most common diseases currently include
- Cataracts
- glaucoma
- Age-related macular degeneration
- sty
- astigmatism
- strabismus
- retinal detachment
- conjunctivitis
- Night blindness
Causes of the diseases
In many cases, genetic predispositions are the cause of a limiting eye disease. Cataracts (cataracts), glaucoma and age-related macular degeneration in particular are often triggered in this way. Smoking in particular is also a significant risk factor. Furthermore, the harmful influence of ultraviolet light is currently assumed to be one of the main causes.
Inflammation can also cause serious diseases. These primarily affect the conjunctiva, cornea or iris of the eye. In rare cases, however, inflammation of the choroid can also occur. However, these then quickly spread to the lacrimal apparatus and the eyelids, affecting almost the entire eye.
Permanent inflammation can lead to pathological clouding of the vitreous humor. In addition, a disease of the eye is also possible without an obvious organic cause. This form of reduced visual acuity is known as amblyopia. Strabismus is usually responsible for this defective vision.
Long-term untreated short-sightedness, long-sightedness and astigmatism also cause a massive reduction in the quality of vision on the retina in many cases.
