PURPOSE: To report on isolated central retinal artery occlusion (CRAO) as an 
initial presentation in two patients with undiagnosed paroxysmal nocturnal 
hemoglobinuria (PNH).
METHODS: CRAO related to the aggravation of PNH was observed in 2 of 98 
consecutive PNH patients for 10 years. Ocular and systemic manifestations were 
evaluated before and after systemic steroid, eculizumab and anticoagulant 
administration with adjuvant ocular treatments.
RESULTS: Two young patients presented with complaints of acute painless 
monocular vision loss. In both cases, fundus examination revealed retinal edema 
and a cherry-red spot in the macula, consistent with CRAO. On systemic 
evaluation, severe anemia and thrombocytopenia were observed, and simultaneously 
thrombogenic processes were suggested by increased D-dimers, fibrinogen 
degradation products and/or portal vein thrombosis. PNH testing of red blood 
cells revealed a CD55 and CD59 deficiency consistent with PNH in both cases. The 
systemic complications typically associated with thrombosis were not observed 
for the following several months with early conservative treatments including 
eculizumab.
CONCLUSIONS: Acute blindness from CRAO can be a unique manifestation of 
undiagnosed PNH and its subsequent aggravation. Systemic evaluations including 
PNH testing, especially in young CRAO patients, are strongly recommended for 
early detection of the further systemic thrombogenic processes.