Astute question...

Basically you are on the right track. Iridology tells you what is wrong, but not really why its wrong.

Depends what you mean by 'black'...

First, you'll see little tears in the threads (these may look black at first depending on eye colour), then they turn in to coloured spots, and at the end (almost no hope of return) you'll have solid dark patches (larger than a spot). Tweet