You have chosen the perfect frames for yourself and all that remains now is to get the right types of lens. For that, you need to know the two basic types of lenses and where they are used.
The two main types of lenses have several subtle differences that end up giving huge differences in their functionality. So let us get started.
What are the Two Main Types of Lenses?
The two main types of lenses found in glasses are Convex or Converging Lenses and Concave or Diverging Lenses. Let us explain how both of them are different.
Of the two types of lens, Convex Lenses are those lenses that have thicker middles and thinner edges. They essentially work like the human eye and converge light rays at one point, known as the focal point, so they are also known as converging lenses.
Since they converge light at one point instead of dispersing it, they have a positive focal length. The focal length is the distance between the center of the lens and the focus of the lens. So basically, since the convex lens converges the light at one point, that leads to a real image and a positive focal length in comparison to the concave lens.
What all this means for the consumer is that convex lenses are used to treat hyperopia or farsightedness.
What happens in farsightedness is that the rays of light passing through your lens are not converged at the retina (inner layer of the eye) by a weak lens of your eye.
Such a patient has no problem viewing distant objects. But to view objects that are nearby the shape of the lens has to change and these patients are unable to do that. This is due to the weakened muscles in the eye that occurs as patient ages.
The convex lens helps such patients by converging light rays at the retina so that they can have a clearer image. The objects also seem to be closer are slightly larger than in reality.
Other diseases where convex lenses could be handy are presbyopia (in reading anti-glare glasses) and aphakia (absence of lens).
The other type of lens one shall see is the concave or diverging lens. These are thinner at the middle and thicker at the periphery. They tend to diverge the light in such a way that they have a negative focal length.
Due to these properties, they are used to treat nearsightedness or myopia. This is often seen in people with excessively long eyeballs or unduly curved cornea thus giving a lens that is too powerful and focuses the image before the retina. These people have no problem viewing near objects but can not view distant objects as clearly.
What the concave lens does in this setting of myopia is that it practically weakens the lens so that the rays of light can focus precisely on the retina.
Other types of Lenses:
These were the two main types of lenses but in reality, optics has advanced a lot and these days there are other different types of lenses used as a combination of these two.
These may be bifocal lenses with two different powers catering to both near vision and distant vision at once.
Another recent advancement has been the trifocal lenses with three different powers for near, intermediate and distant vision. These two tend to take some time adjusting to them but can be truly life-saving for some.
Other varieties like computer lenses for blue light protection or anti-glare reading lenses to reduce reflection in lenses while reading or driving are also contemporary types of lenses.
By now you must have a precise idea of the two main types of lenses and their basic differences and uses.
Convex and Concave lenses are used regularly to correct visual errors like farsightedness and nearsighted Bess respectively. In practice, they are often used together for complex visual diseases.
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