By this logic we are speculating that perhaps being blind from birth blocks the symptoms of schizophrenia to the point that it is no longer a "disease". I don't know if this is correct, but a compelling idea.

Yeah that would be the speculation: that blind schizophrenics are asymptomatic.

I think you are assuming that significant distress will result in awareness that the distress is medically significant.

I have no assumptions about schizophrenia, I just paraphrased how the definitions of the ICD-10 work. The fact of suffering is the distinction between a mental disorder and a quirky personality.

Think of it as a continuous spectrum from the idealized normal person (the center of a bell curve) to the person having significant problems living a normal, fulfilling life. The eccentric personality is somewhere in between.

This is all about definitions. The ICD-10 and similar categorizations essentially work by listing a number of symptons and a minimum count of symptoms a patient has to have to be diagnosed according to this definition. They don't make any assumptions about disorders existing per se.

It can be distress which is missed by the doctor.

I think it's far more acceptable for us to "mishear" something and think nothing of it. The seeing also have the backup sense, sight to verify much of what we hear.

"I heard the sound of an elephant stomping around in my living room."

This statement made by a seeing person could be made by nobody thinking much of it. I wouldn't immediately ask if they actually thought an elephant were in the living room at the time.

The same statement made by a (blind) schizophrenic person could have implied that the person actually believed there was an elephant in the living room, but the clinician might have missed the significance and not asked follow up questions.

A bit of a contrived example, but you get the gist.

To a seeing person it might

This theory depends on hundreds, maybe thousands of doctors and peditricians, many of whom would be specialists focusing on blind patients, a similar number of teachers, social workers, care takers, blind training centers staff, parents ... ALL missed schizophrenia, which is often a debilitating illness, because they are "sighted".