How the Eye Works

When it comes to our eyes, it can often be easy to overlook the basics. But knowing how our eyes work can help us to understand how refractive errors and eye conditions affect these precious organs. So, let’s take a closer look at how the eye works.

Your eye is like a camera

Your eye is made up of millions of parts that all work together to create the images we see of the world around us. But the most important parts of the eye include:

  • A variable opening called the pupil;
  • A lens system, including a transparent covering (the cornea, which does most of the focusing) and a spherical lens inside the eye, behind the iris (the coloured part);
  • The retina – a complex layer of cells at the back of the eye which acts as the ‘reusable film’ in a camera;
  • Various sets of muscles – control the size of the pupil, the shape of the lens system (to control the ‘zoom’ function of the eye) and the movements of the eye.

As we take in the images of the objects around us, light passes through the cornea and the lens of the eye via the pupil.

The spherical lens, situated in a sac between the pupil and the retina, refracts this light and focuses it on the retina. From here, sensory cells in the retina, called rods and cones, change the photons of light into electrical signals.

Nerves connecting the eye to the brain transmit these signals to the brain, which interprets them as an image.

When you look at something, four things must happen in order for you to make it out clearly:
  • The image must be ‘reduced’ to fit onto the retina;
  • The scattered light must be focused on 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, giving us our vision.

For all the above to occur effectively, the muscles attached to the lens contract and relax, changing the shape of the lens system. This keeps the object focused on the retina, even when your eyes move. This complex set of muscle movements is controlled by the nervous system.

Cataracts occur when the spherical lens inside the eye becomes clouded. 

As we get older, our vision can begin to deteriorate. This can be due to a number of changes. For example, presbyopia occurs when the focusing power of the lens begins to weaken. Cataracts also affect the lenses, causing impairment in vision.

Over time, proteins in the lens begin to break down. Eventually, these broken-down proteins clump together, forming a cloudy obstruction inside the spherical lens of the eye – called a cataract.

As the cataract worsens (a process that can take a number of years), light eventually becomes unable to pass through the lens effectively. This causes blurriness in your vision and, if left untreated, can eventually cause blindness.