What is +plus and -Minus number of eyeglasses??
Some people have trouble to see pictures clearly with naked eyes. So we visit Dr. for eye checkups after eye checkup Dr. provides us a number that can be + or - . Had you ever think ЁЯТн what's that number means? And how numbers glasses help us to see pictures clearly.
How eyes work?
Our eye has a lens so all the rays coming from the object are going through a lens and projected on our retina and we can see objects clearly.
Fig. 1 (Source -Google)
Why some people trouble to see object that is far or near?
Our shape of the lens is adjusted so that the rays coming from the object are exactly projected on the retina. But for some people, The shape of eye lens get disturbed ( Shape can change due to continues T.V or Mobile watching or genetic) due to shape change rays coming from object are not projected exactly on retina. So we can't see the object properly. If rays projected before the retina then then we can't see the object which is away from us clearly and if object rays projected after the retina then we can't see the object clearly which is near to us.
How eye glasses minimize this ?
When we wear the eye glasses the glass is designed in such a way that the rays coming from object get projected exactly on the retina. And we can see the object clearly.
Fig. 2 (Consider lens mention in B and D as eyeglasses)
In Fig. 2 diagrams A and B in that object is away from the eyes. In diagram A rays coming from object are not projected exactly on the retina. It is projected before the the eye retina at postilion I, mention in the diagram. We can see pictures clearly when rays projected exactly on eye retina and to do that we wear eye glass (Double Concave) .In diagram B you can see that after putting the lens (eye Glasses) between objects and eye lens, the rays coming from object are getting exactly projected on the retina and we can see the picture clearly.
In Fig. 2 diagram C and D object is near to the eye. and rays are projected behind the retina of the eye. If we wear eyeglasses (Double Convex) then rays projected exactly on retina of eye and we can see nearer object clearly.
In Fig. 2 diagrams A and B in that object is away from the eyes. In diagram A rays coming from object are not projected exactly on the retina. It is projected before the the eye retina at postilion I, mention in the diagram. We can see pictures clearly when rays projected exactly on eye retina and to do that we wear eye glass (Double Concave) .In diagram B you can see that after putting the lens (eye Glasses) between objects and eye lens, the rays coming from object are getting exactly projected on the retina and we can see the picture clearly.
In Fig. 2 diagram C and D object is near to the eye. and rays are projected behind the retina of the eye. If we wear eyeglasses (Double Convex) then rays projected exactly on retina of eye and we can see nearer object clearly.
Depending on rays projected after the retina or before the retina Dr. Provide us the eye glasses number in + or -. If we have trouble to see a picture which is far more, Then Dr. provide us number in - and If we have trouble to see a picture which is far more then Dr. provide us number in + And after wearing eye glasses, rays are projected exactly on eye retina and we can see objects clearly.
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