Some quick numbers:

  1/2500    .. What is the probability of being born blind?
  1/100     .. What is the probability of having schizophrenia?
  1/250000* .. What is the probability of both?
  1/250000* .. What is the probability of both + having resources to have it diagnosed?

So, in the US:

  340MM people -> 1360 born-blind people who would develop schizophrenia

So call it 700 people in the US alone. If it is in fact zero, that is significant!

I chose the US because 100% people will have adequate access to this level of medical care. A formal diagnosis is not the same thing as access, but a born-blind person either has parents/family, or has a state warden with access to care. This is also true in many many other countries, but certainly not all.

The US has 4.1% of the world population. Figure 50% of the world does not have this level of medical access. It's probably less than that, but maybe not.

This suggests about 10,000 people worldwide, living today, who would be affected, and in an environment where they would be diagnosed.