The following represents my interpretation of a video released by Nigel Cowood: Nigel Cowood shares many ideas with Josef Hofmann, a German eye sign enthusiast.
Nigel Cowood looks for:
a pupil
the eye sign circle
with speed lines
and distance lines
a thick, cratered, junky iris with a big step toward the eye sign circle
with breeding grooves and craters
For Nigel Cowood:
the color of the eye means nothing as every color breeds winners and wins races
the circle of correlation is just part of the iris
the width of the eye sign circle does not matter
If a bird has 2 wings it has the potential to win races. The eye is only a fraction of the whole scenario. The eye of a breeder, however, must show breeding qualities.
one cannot reliably grade an eye before the bird is 12 to 18 months old as the eye needs to mature
the eye sign circle shows the racing potential through its speed and distance lines
the iris shows racing and breeding potential
the outside circle is not important as many good breeders do not have it
serrations do not count for anything
Eye sign is useful for getting a higher percentage of good flying birds than by using some other methods. The problem with pairing birds with a well developed iris together is that the iris of the offspring begins to overflow onto the eye sign circle and eventually obliterate it.
It is therefore best to pair a breeding eye to a racing eye which will produce many good racers and the odd good breeder.
The iris in a racing eye is flat and of uniform color.
The iris in a dual purpose eye or a breeding eye is built up and shows lines and craters with a large step down toward the eye sign circle.