Know your eye

  • A black-looking aperture, the pupil that allows light to enter the eye.
  • A colored circular muscle, the iris, which gives us our eye's color. This circular muscle controls the size of the pupil so that more or less light, depending on conditions, is allowed to enter the eye.
  • A transparent external surface, the cornea that covers both the pupil and the iris. This is the first and most powerful lens of the optical system of the eye and allows, together with the crystalline lens the production of a sharp image at the retinal photoreceptor level.
  • The "white of the eye", the sclera, which forms part of the supporting wall of the eyeball. The sclera is continuous with the cornea.
  • A cross-sectional view of the eye shows three different layers
    1. The external layer, formed by the sclera and cornea
    2. The intermediate layer, anterior (iris & ciliary body) and posterior (choroid)
    3. The internal layer, or the sensory part of the eye, the retina


  • Three chambers of fluid: Anterior chamber (between cornea and iris), Posterior chamber(between iris, zonule fibers and lens) and the Vitreous chamber (between the lens and the retina). The first two chambers are filled with aqueous humor whereas the vitreous chamber is filled with a more viscous fluid, the vitreous humor.
  • The lens which is a transparent body located behind the iris. It is suspended by ligaments, the contraction or relaxation of which, changes the shape of the lens, a process called accommodation that allows us to form a sharp image on the retina.
  • Light rays are focused through the transparent cornea and lens upon the retina. The central point for image focus (the visual axis) in the human retina is the fovea. Here a maximally focused image initiates resolution of the finest detail and direct transmission of that detail to the brain for the higher operations needed for perception.