Marek's causes the COLOR of the Iris to change to gray.
http://msucares.com/poultry/diseases/disviral.htm
Quote: You can easily test to see if the pupil is reactive by taking her into a dark area and shining a light in her eye to see if the pupil expands and contracts
http://msucares.com/poultry/diseases/disviral.htm
Quote: You can easily test to see if the pupil is reactive by taking her into a dark area and shining a light in her eye to see if the pupil expands and contracts