How it works: the eye
Posted on 26 April 2016
You can see this text on your screen, right? Ever wondered how that happens? Here’s a look at how your eyes work – with a special focus on its lenses.
Very basically, your eyes work like this: light enters through the cornea, which bends the light rays so that they pass freely through the pupil (the opening in the centre of the iris). From there, the light rays pass through the eye’s crystalline lens (which is made up of a water-soluble protein) and then into a thick gel-like substance (the vitreous), which fills the globe of the eyeball. The light rays finally end up at your retina, which processes those rays via millions of tiny nerve endings, and then sends impulses to your optic nerve.
Simple, right? So to recap: the picture comes in at the cornea, then gets processed at the iris/pupil, focused at the lens and projected onto the retina. (Funny story: when the ‘image’ lands at your retina, it’s upside down! Your brain has to flip the picture back to being the right way round.)
Now if one of those parts doesn’t function properly, you’re not going to get a clear image. Take the lens, for example. The lens helps to focus the light/image on the retina, so if your lens gets clouded, the image you see will be blurred. This is called a cataract and it’s what causes about half of the blindness (and 33% of the visual impairment) around the world. ‘A cataract is basically when your lens goes hazy,’ says Dr Burnet Meyer, an ophthalmologist at Mediclinic Durbanville. As an ophthalmologist, Dr Meyer would perform cataract surgery in this case, removing the cloudy lens and replacing it with a clear, artificial replacement.
‘That replacement lens looks like a contact lens, but it’s inserted into the eye – right into the “bag”, as a natural lens,’ he says, explaining how the new lens helps to provide the required focus for the patient’s visions. ‘It’s a central contact lens, with two little haptics on the sides, which act as spring coils. So when you insert it into the bag, the springs open up and maintain their position inside the bag. The calculations are done prior to the surgery, and the lens is selected according to those values. The lenses are individualised for each eye.’
‘When you replace the lens, you replace as much of the spectacle value as possible,’ Dr Meyer adds. ‘So after cataract surgery, most patients end up only needing reading glasses. In and around the house, they’d be able to function as normal without needing specs.’
That’s the good news – after cataract surgery a patient will end up with even better vision than before because the new lenses are custom-made. The even better news is that cataract surgery is – in Dr Meyer’s words – a ‘painless’ and ‘user-friendly’ procedure.
‘It’s performed under a local anaesthesia, whereby we numb the socket of the eyeball,’ he says. ‘The surgery itself is classified as microsurgery, which very simply means we work through a microscope and it only takes about 15 minutes. The wound heals within 12 hours, and when the patient opens their eye again, they’ll be able to see clearly again.’