As we know dispersion is caused by a convex lens.our human eye also has a convex lens so dispersion must take place in eye also this leading to a formation of blurred image on retina.then why are we able to see clear images?
The linked answers address the question well, but I want to specifically call out that dispersion is not a property of the shape of the lens (i.e convex, concave, plano-convex, etc.) but rather the material the lens is made of (N-BK7, fused silica, silicon, etc). A concave lens of the same material would have an identical dispersion curve/change in index with wavelength.
You “see” with the optics of your eyes plus the processing of your retinas and brains.
Because normal color vision has enough color acuity to distinguish the separate dispersed colors on the retina, the processing takes it out. “Ah, I see tight concentric color rings, I’ll see that as a white dot!”
This is the source of some optical illusion effects. The boundary between orange and blue half-planes looks weird, for example, because this correction doesn’t work right.
It also explains why green-deficient color blind people often see much better with tinted glasses. Their processing system doesn’t get the raw color info that lets this correction work: the green part in the middle is just luminance (“white”) information, so the end up perceiving less precisely-corrected dots and edges.