Hi @Midnightman14 and welcome to the peafowl forum!
This is actually a really old thread (it was started in 2011). We dragged it back up because a frequent poster had a bird that developed blindness recently.
As far as I know, it is not a glandular dysfunction, and it is not necessarily an interaction with the pied gene. Some cameo (and later. some peach, which originated as a cameo cross) carried a genetic defect which resulted in blindness -- it was sometimes informally referred to as the "cameo death gene" even though it didn't actually cause the birds to die. It caused the birds to go blind, some younger, some older. Blind birds tend to die early, and owners didn't necessarily realize their birds had gone blind. They would notice the birds failing to thrive, or find them with broken necks. It seemed to be associated with a progressive whitening of the bird -- informally referred to as a "progressive pied" -- but as far as I know, there has not been any genetic research published or reported on. Because some birds did not display the blindness until fairly late in life, they had sometimes produced offspring, which then spread the gene further. I am not sure whether all the birds which went blind also had the progressive whitening or not. It's quite different from what we refer to commonly as the "pied gene."
My impression is that most folks have made a fairly diligent effort to remove affected birds from the breeding gene pool, so it is perhaps less common now, and hopefully will be even less common in the future. It never affected all cameos or all peaches -- only some birds and/or some breeding lines, and it was obviously genetically passed down based on owner/breeder info published here on BYC and formerly on the UPA forum, (which has since disappeared, but which used to have good info).
If you are interested in cameo and peach birds, I would recommend that you research them carefully before you buy, ask questions and have a look at the parents if you can. I would also be careful about any bird advertised as "progressive pied" (that is not the typical pied pattern that we see in peafowl) since it is unclear whether the particular gene or set of genes that causes a "progressive pied" also is responsible for the failure in the eyesight. I've seen one suggestion elsewhere that made that argument, but I simply do not know. I keep hoping someone will actually do the research on this one, but haven't heard of it happening thus far.
Glad you have joined us