Understanding the eye
To understand how contact lenses work, you first need to understand a little about the eye. At its most basic, light reflects off an object and passes through the cornea, the transparent covering of the eye. Next it travels to the pupil, the black part of the eye, and then through the lens, which focuses the rays on the retina at the back of the eye.
The retina is filled with things called rods and cones and these take the light and convert it to electrical impulses which are then sent to the brain for processing. When you get blurred vision, this is due to something called ‘refractive errors’ and is when the shape of the eye stops the light reaching the retina directly and leads to distortion.
Fixing those errors
So to fix those errors, we use a tiny plastic lens that corrects them by creating a film that makes contact with the eye (hence – contact lenses). They work in the same way as glasses to focus the light on the retina and allow the eye to work properly. There are a number of different types of errors that leads to different problems and require different prescriptions to correct.
Myopia or near-sightedness is where object far away appear blurred while objects close by seem clear. This happened when the light entering the eye isn’t correctly focused and is caused by the shape of the eye. This is one of the most common conditions and there are various contact lenses that correct it.
Hyperopia or farsightedness is the opposite, where items close by are blurred but those further away are clear. Again, this is relatively common and there are lots of lenses to correct it.
Presbyopia is an age-related condition similar to hyperopia where items close by become blurry but comes from a different cause. While hyperopia comes from the shape of the eye, presbyopia comes from the eye lens hardening with age. To correct the condition, multifocal lenses are often used as they can clear both the near and the far blurriness.
Finally, astigmatism is a condition where the irregular shape of the cornea or the lens stops the eye from focusing the light on the retina. A special category of lens is used to correct this condition, called a toric contact lens. Often, an image of a ball can be used to visualise the different – a sphere lens is like a beach ball where a toric lens is more like a rugby ball. An example of lenses to correct this condition are the Biofinity Toric lens.