Mydriasis and heredity.

Routine ophthalmoscopy and fundoscopy of 673 individuals revealed 42 whose irides failed to dilate to a clinically useful degree within 25 to 30 min after the administration of drops of 1% mydracil. These individuals occurred with different frequency among the Aymara, Mestizo, and non-Aymara groups which made up the sample of examinees. The phenomenon was most common among the Aymara, less common among the Mestizos, and least common among the non-Aymara. Distribution of affected individuals within the three groups suggests that the trait is inherited.