It can be easy for us to take our eyes for granted – especially if you’re one of the lucky ones who has escaped the need for glasses or contact lenses. However, knowing how these impressive organs work can help us to understand how common eye conditions such as cataracts affect them. So, with that in mind, let’s take a closer look at how the eye works.
Your eye is like a camera
Each of your eyes is made of millions of parts that all work together to give us one of our most important assets: our vision. The most important parts of the eye include:
- A variable opening called the pupil – the black circle in the middle of the eye;
- 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) at the front of the eye;
- The retina – a complex layer of photo-sensitive cells at the back of the eye which acts like the ‘reusable film’ in a camera;
- Various sets of muscles – control the size of the pupil, the shape of the lens system (controlling the ‘zoom’ function of the eye) and the general movements of the eye.
When we look at the space around us, light bounces off objects and enters the eye through the cornea and lens via the pupil. The cornea and lens (located in a sac between the pupil and the vitreous) work together to refract the light and focus it on the retina.
This photo-sensitive layer features sensory cells called cones and rods that translate light photons into electrical signals. These signals are then transmitted to the brain through nerves connecting the two organs where they can be processed into images.
In order for this process to work effectively, four things must happen:
- 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.
The muscles in our eyes play a vital role in this process. When the muscles attached to the lens contract and relax, they change the shape of the lens system. This keeps the light reflected from an object focused effectively on the retina, even when we move our eyes. These muscles are controlled by the nervous system.
Cataracts occur when the spherical lens inside the eye becomes clouded.
As we age, our vision begins to naturally deteriorate. This can be down to a loss of focusing power as the muscles in the eye weaken (presbyopia), or due to cataracts – the clouding of the eye’s lenses.
Cataracts occur as the proteins in the lens begin to break down and clump together. When this happens, the proteins will gradually form a cloudy obstruction in the eye, eventually causing significant vision impairment.
Over time, cataracts become more severe, preventing light from passing through the lens effectively. Eventually, treatment will be required to remove the cataract and restore vision. If left untreated, cataracts can cause vision loss and even blindness.