Question

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

Answer 1

When the curvature of the eye lens is excessive, than the focal length of eye decreases. This results in the formation of image in front of the retina. This whole situation makes the image blur and causes myopia. 

Answer 2

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.