A vandal-proof dome camera is built to withstand deliberate or accidental impact, usually through a reinforced housing and a polycarbonate dome. The impact rating describes the force the housing tolerates, and it says nothing about image quality or how the dome ages outdoors.
The dome is the exposed part, so it takes the abuse. A hardened housing protects the camera inside, but a scratched or sun-damaged dome quietly ruins the picture it was bought to protect.
Reading the impact rating
IK ratings run from 01 to 10 and quantify resistance to impact energy. A higher rating means a tougher housing rather than an unbreakable one, and the mount matters as much as the dome.
What the rating misses
Ultraviolet light turns polycarbonate yellow, cleaning chemicals scratch it and gaskets dry out. Inspect the dome at each service visit, and replace it when the image turns hazy rather than raising sharpness.