This line of thinking is just hopeful projections of desired causality.
Such changes are replicated more successfully (more offspring) making the change/mutation more resilient to disappearing from the genepool.
Over time any organism that's living/thriving is going to have a lot of these mutations stacked on top of one another in a resilient way(size of population with the same mutations). Any mutations that are disadvantageous to natural selection and proliferation are weeded out of the genepool (go extinct)
I don't know if you're being somehow pedantic for some definition of "eye" or "evolve", or if you're one of those "Intelligent Design" creeps.
Evolution can be very easy given time. Trees independently evolved from non-tree plants something like 100 times, for example.