Eye Structure And Function

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Eye Structure And Function
Eye Structure And Function
Video: Eye Structure And Function
Video: Structure of the Human eye | Don't Memorise 2023, February

The eye: structure and function

The eye consists of many different structures that perform various tasks in a complex interplay - e.g. protecting the eye and supplying it with nutrients. Last but not least, they are essential for seeing and thus for orientation.

How indispensable the individual structures are and how intertwined the interaction is, is noticeable at the latest when something no longer works optimally and the help of an ophthalmologist has to be sought.


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  • Important structures
  • The eyeball
  • Vitreous & aqueous humor
  • Iris & Lens
  • Protection & mobility

Important structures

The numerous structures in the eye are necessary so that, ideally, sharp and colored images are created. These structures include:

  • the eyeball with leather, veins, cornea and retina, vitreous humor and aqueous humor,
  • Iris and lens,
  • Eye socket, eyelids, conjunctiva and the lacrimal system,
  • the eye muscles and
  • the optic nerve. Graphic structure eye © bilderzwerg

The eyeball

The eyeball is almost spherical and about 24 mm long in adults. Among other things, it is surrounded by a shell that consists of three layers that are important to the eye:

  • The leather skin (sclera) and cornea that surrounds the outside of the eyeball. The dermis has a firm fabric and serves to protect the eye from physical influences (e.g. impact) to a certain extent. In the front area of ​​the eye it merges into the transparent cornea, which protects the eye to some extent from radiation (UV radiation). Together with the lens, the cornea forms the optical system of the eye - that is, by and large, the cornea and lens are responsible for the fact that light hitting the eye is refracted and shown reduced on the retina. For this, the cornea is curved and protrudes beyond the eyeball.
  • The choroid, which is extremely vascular, supplies the retina and keeps the temperature of the eye constant.
  • Retinawhich is located in the back of the eye. It has an essential function in seeing. Receptors in the retina (cones and rods) make it possible to see something or at least recognize contours and distinguish colors and shades during the day, twilight and even at night. The so-called yellow spot (macula lutea), the point of sharpest vision, is located on the retina. The optic disc, where the optic nerve emerges from the eye, is also on the retina. This site does not contain any photoreceptors It is known as a blind spot because one arises in the field of vision. However, this is not noticed as it is balanced by the brain. The optic nerve is the connection to the brain.Information (light) is converted during the visual process and passed on to the brain via the optic nerve.

Vitreous & aqueous humor

The vitreous body fills the inside of the eye - and takes up a large proportion of the space between the lens and retina. It consists of a gel-like substance with fine collagen fibers. Its structure diminishes somewhat with age and becomes more fluid. The vitreous humor collapses and detaches itself from its attachment to the retina (posterior vitreous detachment). This can happen earlier, for example in the case of high myopia or a bruised eye. In addition, retinal tears and detachment can occur.

The intraocular pressure is largely maintained by the aqueous humor of the anterior and posterior chambers of the eye. The eye needs this pressure in order not to collapse and to keep its almost round shape, which is necessary for optimal vision. The aqueous humor is constantly formed and is important for the supply of the cornea and lens with nutrients. If the drainage of the aqueous humor does not work properly, the fluid backs up and the eye pressure increases - as in glaucoma (glaucoma).

Iris & Lens

Various structures of the eye are important for the visual process. The fact that an image can be perceived in focus and with sufficient brightness is due to the iris and lens of the eye, among other things.

The iris, which is in front of the lens, has an opening in its center, the pupil. Through these light comes into the eye. It narrows when it is bright and expands when it is dark or twilight. It is also necessary for close-ups where it also narrows and thus provides more depth of field.

The lens behind the pupil refracts the light so that it strikes the retina in such a way that a sharp image is created - regardless of whether you look into the distance or look at something nearby. To do this, the lens changes its curvature (shape). It is elastic and connected to the ciliary body via the zonular fibers. If the eye is directed closer, the ligaments of the ciliary body are loosened by tensioning the muscle fibers. The lens bulges more and takes on a more spherical shape. The anterior chamber flattens out somewhat, the pupil is narrowed. Overall, the refractive power increases. Objects in the vicinity can be seen clearly. When looking into the distance, the lens flattens out again because the ligaments of the ciliary body pull the lens. The muscles are not active.

The ability of the eye with the help of the lens and its adjustment (refractive power) to be able to sharply image objects at different distances on the retina is also known as accommodation. The eye can change the refractive power so that objects near but also far away can be perceived clearly.

Protection & mobility

The eye (more precisely: the eyeball) lies - padded with fat and connective tissue - in the bony eye socket (orbit). The eye is also protected by the eyelids, which reflexively close when the cornea is touched and can thus keep foreign bodies away. The two folds of skin (upper and lower lobes) are connected to the eye and, thanks to their mobility, protect against strong light. The tear fluid is also distributed through permanent opening and closing of the eyelids. It prevents the eye from drying out and helps to ward off germs, helps remove foreign bodies and cleans the eye. The tear fluid also contains nutrients. It is formed in glands that are on the sides above the eyes and is wetted when the eyelids are moved from top to bottom,the eye (cornea, conjunctiva). It flows on the inner edges of the eyelids through two small openings (the lower teardrop points) and the tear sac into the nose. The conjunctiva also covers a small part of the eyeball. It is connected to the inner side of the eyelid via the cleft of the eyelid.

Turning the head makes it possible to expand the field of vision. But the eyes are also mobile so that the surroundings can be viewed. To do this, six different muscles are attached to the eye, some straight and some at an angle. With their coordinated help, it is possible to get an overview.

Further information:

  • Graphics, images and details about the eye can be found at MedUni Vienna.
  • Information is also available on the website of the Austrian Ophthalmological Society.

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