There are glasses for myopia. They are double spherical concave lenses, which have negative diopter and serve to correct shortsightedness (also called myopia). If a person has myopia, there is s discrepancy between the break force of the eye and the front-back size of the eye. The image is formed in front of the retina and people see it blurred like in fog.
Glasses used for hypermetropia. The convex spherical lenses with positive diopter serve to correct long-sightedness. In hypermetropia image is formed behind the retina and people have troubles seeing nearby.
There are also glasses made for reading. When people are over the age of 45 it is observed long-sightedness that is also called presbyopia. Here, the elasticity of the lens of the eyes is impaired and they are not able to change the break force. The image is formed behind the retina. For the hypermetropia, people use compound lenses. Recently glasses with smooth transition, called progressive, have been produced.
Sunglasses – they are used to protect the eye from the increased light. The first sunglasses were sold in 1929. The cheap and poor quality sunglasses are made of plastic, which easily allows the UV rays to pass through. You should pay attention to what sunglasses you buy. They should be with a good protection, otherwise they can damage your eyes. Mirror sunglasses reduce light reflections from the snow, sand and water. The most common combination is the photo chromic glasses, which get darker when the illumination is increased.
Another type of glasses are the sport glasses which can be divided into glasses for summer sports and winter sports. Swimming glasses are those for water sports. If you need to see normally underwater, you need air layer. The first prototype of swimming glasses dates back from a long time ago. Except the fact that they provide normal vision underwater, they also protect the eyes from harmful substances like – the salt in the sea and ocean basins. Modern glasses for swimming are two types: silicon and neoprene. There are glasses for swimming with diopter for people with poor eyesight. Many winter sports like skiing, snowboarding and mountaineering require wearing special glasses. Lenses of these glasses are made of polycarbonate and have several coverings – against fog, bright reflections of snow and ice and a layer that protects them from scratches. Practicing winter sports without glasses is very dangerous.