How does the eye work?

Have you ever wondered how your eye functions?

Although the human eye is much more complex than any man-made machinery, in simple terms it can be compared to a camera.

Light coming from outside enters the eye via the pupil. The pupil adapts to the level of brightness in the environment, varying in size to let more or less light into the eye.


At the back end of the eye, the retina acts as the image sensor. Its surface is covered with about 120 million photoreceptor cells that react to light intensity (these are called rods) and 6 million cells that enable us to see colours (these are called cones).

  • Anterior Chamber Space located between the cornea and the iris, filled with a watery fluid, the aqueous humor. This liquid helps to refract light rays.
  • Cornea Transparent front side circular area in the sclera where light enters the eye. It covers the iris, the pupil and the anterior chamber of the eye.
  • Iris Coloured smooth muscle surrounding the pupil. The iris contracts and dilates according to the brightness of the light and to allow more or less light to enter the eye.
  • Angle of the Anterior Chamber Area of the anterior chamber where the cornea and iris join.
  • Pupil Orifice in the middle of the iris, where light enters the retina.
  • Zinn's Zonule Ring of fibers connecting the ciliary body and the crystalline lens.
  • Crystalline Lens Transparent, flexible and bi-convex lens that concentrates light rays on the photoreceptor cells of the retina.
  • Ciliary Body Smooth muscle that modifies the curvature of the crystalline lens and in doing so allows a better accommodation of the eye.
  • Sclera or 'white of the eye' Outer white and opaque membrane, covering the eyeball. It protects the eyeball and muscles attached to it control the eye's movements.
  • Retina Light-sensitive inner membrane, it hosts photoreceptor cells (rods and cones).
  • Macula Small area at the center of the retina, highly concentrated in cones. Its diameter is around 2 mm. The center of the macula is the Fovea Centralis, exclusively composed of cones and offers the sharpest vision.
  • Vitreous body Gelatinous fluid filling the space between the lens and the retina. It helps to maintain the retina against the eye wall and the intraocular pressure.
  • Blind Spot
  • Optic disc Part of the retina where the optic nerve fits into, as blood vessels. This area is also called the blind spot because there are no receptors in this part of the retina.
  • Central retinal vein Vein that runs through the optic nerve and drains blood.
  • Optic nerve Nerve that transmits visual information (electrical signals) to the brain.

Light is focused on the retina by the crystalline lens, which is equivalent to the lens on a camera. When the lens is well-shaped and fits the length of the eye, sharp focusing on the retina results in a clear image.

Like a modern camera, the crystalline lens includes an autofocus system. Muscles around the crystalline lens can bend it in order for the eye to focus at up-close distances.


A normal eye can see at far distances without muscular effort, but when looking at near distances, these muscles are constantly contracted. Imagine trying to take a macro photo with your phone’s camera: sometimes it struggles to properly focus on subjects up-close, and our eyes are no different!

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