Type A PRA is a difficult form of retinal atrophy as it appears to have incomplete penetrance or possible dominance - i.e. some carrier animals appear partially affected when examined clinically. An abnormal "shine" has been reported, in the dog's eyes. Disorientation is also common symptom of PRA, particularly at night. Initial night blindness will progress slowly to day blindness. Some Miniature Schnauzers with this disorder are homozygous for the gene for phosducin. However, since some affected dogs are heterozygous for this mutation, and other affecteds are homozygous for the normal allele, it is uncertain how or if this mutation has anything to do with the disorder. (source: Zhang et al 1998)