Eyes Anatomy and Function

In the following, “eyes-ocular appendages” describes diseases that are assigned to this category according to ICD-10 (H00-H59). The ICD-10 is used for the International Statistical Classification of Diseases and Related Health Problems and is recognized worldwide.

Eyes-ocular appendages

Vision is an ability that helps us cope with our lives and daily routines. The sense of sight provides 80% of the information – the other senses are secondary to it.

Anatomy

The human eye includes:

  • Eyeball (bulbus oculi) – the interior contains the lens (lens oculi), vitreous body (corpus vitreum), eye chambers (camera anterior bulbi and camera posterior bulbi)
    • Outer eye skin (tunica fibrosa bulbi, tunica externa bulbi).
      • Sclera (sclera)
      • Cornea (cornea)
    • Middle eye skin/Uvea (Tunica vasculosa bulbi, Tunica media bulbi).
      • Iris (iris)
      • Corpus ciliare (ciliary body)
      • Choroid (choroid)
    • Inner eye skin / retina (Tunica interna bulbi).
  • Optic nerve (optic nerve or 2nd cranial nerve/N. II).
  • Eye appendages
    • Eye muscles
      • Outer eye muscles – used to change the direction of gazeInner eye muscles – used for accommodation (near and far adjustment of the eye) and pupillomotor function (change of the pupil, depending on the incidence of light)
    • Eyelids – upper and lower eyelid; they prevent dust and sweat from entering the eye.
    • Conjunctiva (tunica conjunctiva).
      • Sliding layer that allows the mobility of the eyeball in all directions.
      • Protection against pathogens
    • Lacrimal apparatus (Apparatus lacrimalis) – tear production, transmission, evacuation.
      • Each eye has two tear ducts that originate from the medial part of the two eyelids (punctum lacrimale superius (upper lacrimal punctum) and punctum lacrimale inferius (lower lacrimal punctum)). These join to form the common lacrimal duct: the tears then “run” into the lacrimal sac (saccus lacrimalis).
      • The nasolacrimal duct (lat. Ductus nasolacrimalis) connects the lacrimal sac with the nose and opens into the inferior turbinate (concha inferior).

The eye is well protected in the bony eye socket (orbit).

Physiology

Vision is only made possible by light. When light hits the eye, it passes through the cornea, pupil, lens, and ultimately through the vitreous humor to the retina (retina). How much light enters the eye is regulated by the pupil or iris, which is located around the pupil and can contract. In darkness, the pupil enlarges to let in more light and in brightness, it shrinks. Light is refracted through the lens. An upside-down image is initially formed on the retina. The retina converts the light signals into electrical signals and sends them to the optic nerve, which in turn sends the information to the visual cortex in the brain. The brain turns the image upside down again.The lens enables distance and near vision (accommodation) by changing its shape.

Common eye diseases

Numerous diseases and aging processes can cause our vision to diminish or even disappear. Even at a young age, vision may begin to decline. A child’s normal vision matures to its approximate final form in the first eight to ten years of life. Only up to this age can the development be positively influenced. The most common diseases of the eyes include:

  • Age-related macular degeneration (AMD).
  • Astigmatism (astigmatism of the cornea)
  • Diabetic retinopathy – disease of the retina of the eye caused by diabetes mellitus, which is associated with deterioration of vision and even blindness.
  • Diseases of the eyelids
  • Glaucoma (glaucoma)
  • Hyperopia (farsightedness)
  • Cataract (cataract)
  • Keratoconjunctivitis sicca (dry eyes)
  • Conjunctivitis (conjunctivitis)
  • Myopia (nearsightedness)
  • Presbyopia (presbyopia)
  • Retinopathies (retinal diseases)
  • Strabismus (squint)

The main risk factors for eye diseases

Behavioral causes

  • Consumption of stimulants
    • Tobacco consumption
  • Psycho-social situation
    • Stress
  • Overweight

Causes related to disease

  • Depression
  • Diabetes mellitus – diabetes mellitus type 1, diabetes mellitus type 2
  • Hypertension (high blood pressure)

Please note that the enumeration is only an extract of the possible risk factors. Other causes can be found under the respective disease.

The most important diagnostic measures for eye diseases

Timely preventive measures at the ophthalmologist help to preserve eyesight.

  • Eye test
  • Perimetry (visual field measurement)
  • Tonometry (intraocular pressure measurement)
  • Glaucoma diagnostics – including methods for measuring intraocular pressure.
  • Slit lamp microscopy – optical device that allows the examiner to view the magnified eye by emitting a beam of light; used to examine the anterior, middle and posterior sections of the eye to retinal areas located far in the periphery.
  • Fluorescein angiography – imaging method for the diagnosis of diseases of the fundus of the eye.

Which doctor will help you?

In the case of diseases of the eyes, as a rule, a specialist in ophthalmology should be consulted.