Question

why light pass through optical centre donot refract

Answer 1

Actually the same happens when the ray passes through optical centre. This can be observed in a thick lens. In thin lenses the perpendicular distance between extended incident ray and extended emergent ray is negligible. So we can say that light ray passes through optical centre without deviation.

Answer 2

Optical centre is a point on principal axis according to which if we take a thick convex lens when a light passes through optical centre it is slightly displaced and parallel to the incident direction and if we take a thin convex lens and the light passes through the optical centre then it is undisplaced or undeviated .