One of the effects of lead poisoning is an inflammation of the optic nerve, which causes those who have it to see bright haloes around light sources  In order to produce the striking yellow effects in his Sunflowers paintings, Van Gogh used Naples yellow, a pigment containing lead
Since in his later paintings, Van Gogh painted bright haloes around the stars and sun, it is likely that he was suffering from lead poisoning caused by ingesting the pigments he used
Van Gogh did not have symptoms of lead poisoning aside from seeing bright haloes around light sources.