The incubation period for Mareks is two weeks, if they show no sign of the disease (even if the necropsy comes back positive) by then they are probably fine. I would recommend looking into Mareks vaccinations for future chicks, ever since we started having ours vaccinated the mortality rates in...
For now I would just keep an eye on them. I wouldn't worry about putting down any more chicks unless they begin to show signs of the disease as well. I would keep them seperate for now and wait for the results of the necropsy to return. If other's begin to show signs the best thing you can do is...
I myself am no expert on the disease, but according to The Chicken Health Handbook, the symptom of greyish eyes is a sign of Marek's. This is some of the information I uncovered in the book.
Symptoms include but are not limited too:
Growing thin while eating well
Stilted gait or lack of...