No person who was born blind has ever been diagnosed with schizophrenia
Just speculating, but being born blind has (in recent history at least) led to a quite sheltered and protected life.  For those cases caused by 'chemical imbalances' (genetic factors), 'sheltering' would not help. For cases that occur in response to the external world (environmental factors), the 'sheltering' might have a shielding effect.If so, then the not-blind vulnerable should avoid stress.