I answered a similar question a while back when a parent was asking about "absence of the fovea" in people with albinism.
The macula
is the small central area of the retina and is used for fine, sharp,
acute central vision. The fovea is the even smaller central area of the
macula which produces the
sharpest vision. Lack of pigment in the eye, as in individuals born
with albinism, causes abnormal nerve connections between the brain and
the eye resulting in abnormal development of the fovea. So in people with albinism, the fovea and macula are not aren't really missing, they are just underdeveloped.
Is that clear as mud? 
Let me know if you have any questions.
Mashawna
http://www.parentofachildwithalbinism.com
