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The Eye


The human eye is a highly complex organ system which is difficult to describe anatomically and physiologically. This article gives you a brief overview about the essentials of the eye.

The eye

The eye ball lies in the orbit, a bony cavity in the skull. The retrobulbar fat (corpus adiposum orbitae) is a fatty tissue that lines the orbit from the inside and contains the vessels and nerves. The eye ball consists of the eye layers, the lens and the chambers.

Two of the main eye layers are the sclera and the cornea. The sclera represents the white of the eye. It is covered by the conjunctiva, a transparent mucous membrane which is important for the distribution of the tear film during the eye blink. Inflammation of the conjunctive (conjunctivitis) caused by bacterial or viral infection may be painful and uncomfortably restrict the patient’s vision.

The cornea protects the eye to some extent. It is part of the optical system and mainly responsible for the refraction of light. Deformation of the cornea may lead to visual disorders.

The retina and the choroidea are essential eye layers as well. Light waves striking the retina within certain wave lengths are transformed into electrical signals and transmitted to the brain via the optic nerve (cranial nerve II) and the so called “visual pathway”. These signals are then processed in the brain and converted to a picture. The choroid contains blood vessels that supply the retina.

The lens plays a major role in the accommodation of the eye, the focusing of close and distant vision. Through contraction and relaxation of the ciliary muscles the lens changes its shape adjusting the refraction of light. Cataract, a common eye disorder affecting the lens, develops slowly over years and necessarily needs to be treated.

The term iris is Greek for “rainbow”. This “pinhole” reaches around the pupil and changes its diameter through contraction. By this means the iris regulates the eye’s adaptation to light and dark.

Muscles of the eye

The anterior and posterior eye chambers are separated from each by the iris but have a connection through the pupil. They are filled with aqueous humor which flows from the posterior to the anterior eye chamber. An obstruction to the flow causes an increased intraocular pressure which may lead to glaucoma. Due to the aqueous humor’s ability of refracting the light it is considered as part of the optical system as well.

The vitreous body is also part of the refractive apparatus. It is a jelly-like material filling the space behind the lens and has a similar refractive index as the cornea.

The eye movement is controlled by different eye muscles which all originate from the orbit.

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Show references


  • Benninghoff/Drenckhahn: Anatomie, Band 2, 16. Auflage (2004), S. 655-701
  • Kahle: Taschenatlas der Anatomie, Band 3, 9. Auflage (2005)
  • Lippert: Anatomie Text und Atlas, 8. Auflage, Urban & Fischer Verlag/Elsevier (2006), S. 346-357
  • Schiebler: Anatomie, 9. Auflage, Springer Verlag (2005), S. 651-658
  • Photo 1: Flickr / helgabj
  • Photo 2: Flickr / Patrick J. Lynch

Author & Layout:

  • Christopher A. Becker
  • Achudhan Karunaharamoorthy
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