Our old golden retriever,wont climb the steps on rv

We have an elderly Golden. Her difficulty with the steps seems to be her declining vision. She will go up the spes if there is a light on the steps, and high contrast so see can discern the situation.
If it is dark or in shadow, forget it. Same with the steps to the dog door at home. Uses them ok during day but barks at the door at night to be let in.