 All animals and plants are sensitive. They detect changes in their environment. This is one of the seven life processes. Any change that is detected is called a stimulus. If necessary, they then respond to stimuli in various ways. For example, if you are too cold, you may put a jumper on. Sense organs in animals have groups of receptor cells which detect specific stimuli. Can you name some human sense organs and what they detect? When the receptor cells of the sense organ are stimulated, they relay this information along nerve cells or neurons to the central nervous system. There are different types of receptor cells which are sensitive to different stimuli. Humans have five senses. Sight, hearing, taste, touch and smell. Sight is the detection of light by our eyes. The different wavelengths of visible light give rise to different colours when interpreted by our brain. This video will discuss four vision problems. Colour blindness, glycoma, cataract and diabetic retinopathy. So let's start with colour blindness. Perhaps you know someone who is colour blind or maybe you are. A colour blind or colour vision deficient person cannot tell some colours apart or may only see the world in shades or tones. But why does this happen? The receptor cells in the retina of your eye are called rods and cones. Rods detect light intensity and cones detect colours. Rod cells are used when there is little light and cone cells help you see colours. The cones in colour blind individuals are either fewer in number or simply absent. Colour blindness can cause people difficulty in everyday life. Most red-green colour blind people won't know if they've cooked a piece of meat rare or well done and they're unlikely to be able to tell the difference between green and ripe tomatoes or between ketchup and chocolate sauce. The second eye condition we're going to discuss is glycoma. This is where your optic nerve is damaged by the pressure of the fluid inside your eye. Most types of glycoma have no symptoms so a regular eye test is the only way to know you have the condition. It can lead to blindness if left untreated. The third condition is cataracts. This is when the lens, a small transparent disc inside your eye develops cloudy patches. Cataracts are more common in older people. Over time the cloudy patches usually become bigger causing blurry, misty vision and eventually blindness. Cataracts can be treated by surgery which can involve replacing the lens with a synthetic one. Finally, diabetic retinopathy which is a complication of diabetes caused by high blood sugar levels damaging the retina. The retina needs a constant supply of blood which it receives through a network of tiny blood vessels. Over time a persistently high blood sugar level can damage these blood vessels. So now you can see how important our senses are to us and problems that can arise with our sight.