Your Eye is like a Camera

The human eye is an incredibly complex organ with millions of working parts. But when looked at in a more simple way, it can be compared to a camera. For example, live a camera, your eye has:

  • A variable opening – the pupil;
  • A lens system – this includes a transparent layer called the cornea (responsible for focusing) and a spherical lens that sits behind the iris inside the eye;
  • A ‘film’-like layer called the retina – a layer of photosensitive cells at the back of the eye.

There are also various sets of muscles that control the dilation of the pupil and the shape of the lens system, effectively controlling the focus and ‘zoom’ functions of the eye.

When light bounces off of objects around us, it enters the eye through the pupil and the lens system. 

The cornea and lens work together to refract this light, focusing it on the retina at the back of the eye. The photosensitive cells that make up the retina (known as cones and rods) translate the light photons into electrical signals which are then sent to the brain via the optic nerve.

The brain can then process these signals into a picture of the world around us, just as a Polaroid camera ejects a photograph (only clearer!).

For the brain to process this image effectively, four things are required:

  • The image must be reduced to fit onto the retina;
  • The scattered light must be focused accurately at the surface of the retina;
  • The image must be curved to match the curve of the retina;
  • The brain must be able to interpret the image.

Muscles attached to the lens contract and relax, changing the shape of the lens system. This keeps light focused on the retina, even when your eyeballs move. This complex set of muscles is controlled by the nervous system.

Most refractive errors occur when the eye is unable to focus light onto the retina effectively. This is most commonly due to the shape of the cornea, the length of the eye, or the elasticity of the lens.

The most common refractive errors are (myopia), long-sightedness (hyperopia), astigmatism, and presbyopia. These errors can usually be corrected with external visual aids such as glasses and contact lenses, or by changing the shape of the cornea with Laser Eye Surgery.