know about eyesights , Myopia,Hypermatropia and Presbyopia We human beings have varying eye sights but of which have been corrected due to the right technology.Here we look at three types of eye sights to understand how they happen and how they have been corrected.
First it’s important to understand how normal sight happens to understand the other three.Images are formed on the retina and the images formed are real,diminished and inverted just like with a camera.
Rays from near objects are clearly focused on the retina which is normal but the distant objects are focused in front of the retina of which the objects appear blurry.
A diverging lens is what is used to correct short sightedness.When this lens is used the distant objects are then focused on the retina as well.
This is opposite of the short sightedness.Here distant objects are formed clearly on the retina whereas near objects appear blurred because they are formed behind the retina.
Converging lenses are the ones used to correct this.They reduce the divergence of rays.They converge rays causing images to be formed on the retina as should thus clear images.
This is when old age kicks in and the eye looses its power of accomidation because of loss in elasticity of the eye’s lens.
Here three pairs of spectacles are used to correct the problem;
a)Diverging lens as explained above,to be able to see distant objects.
b)Converging lens so as to be able to see near objects clearly.
c)A pair of bi-focal lenses can be used as well.These glasses are special glasses with the converging lenses toward the lower part of the frame.