Question

how do excessive curvature of the eye lens and elongation of eyeball contributes in myopia???explain in detail.

Answer 1

Convex lens of a focal length F, and the object at infinity. The image should form at the point F for focus. 

But if the focal length decreases, excessive curvature causes the focal length of the eye lens to decrease. Which causes the image to form at a point in front of the retina so we are not able to see a clear image. 
hope it helped uu!!!

Answer 2

Because of excessive curvature of the eye lens and elongation of eyeball, our eyes get stressed and they get difficulty in focusing on any particular point. thus this contributes to short sightedness or Myopia.
Hope this helps