Answer:
Iridology is not so much a form of diagnosis as it is a form of analysis. An Iridologist is not allowed to diagnose, nor should we be able to, as that would limit our ability to see things as they really are. I say this because I see what harm the ability to diagnose has done to the medical profession. Too often, once a diagnosis is made, the search for the root of the problem is no longer sought, instead all efforts are turned toward treating the symptoms.
With Iridology, we see the effects that have manifested from certain actions in specific areas of the body (as seen in the irids), from here we can ascertain the current condition of the said area(s) and analyze the direction in which the current condition is likely to head, thereby determining how best to divert to a more desirable outcome.
A good Iridologist will take each piece of the offending problem/ailment/symptom apart to examine it and it's root cause, measure in all other events that were &/or are taking place in the body - analyze all the information that is being delivered by both the eyes and the rest of the body, do a complete analysis of the gathered information and make several suggestions as a result first of the present condition of the body, and then make adjustments to those suggestions in accordance to the results obtained and the body's ability to carry on with less or no more intervention by us.
So in conclusion I would say 'diagnosis' would not be an accurate definition for what a well trained, professional Iridologist does.