In the Material Room:

Select the figure from the Object Menu.
From the Material drop down menu, select the eye. (Depending on the figure, it might be Eye, it might be Iris, etc.)
Click on the Diffuse_Color node plug and draw it out slightly.
Select New Node->2D textures->image_map.
In the new new box that comes up, click on the word None on the Image Map line.
You get a new screen where you can browse to the eye texture to load it.

(It sounds harder than it really is.) Cheers!