Subjects with albinism were randomly assigned to one of three treatment arms : levodopa 0.76 mg/kg with 25 % carbidopa , levodopa 0.51 mg/kg with 25 % carbidopa , or placebo and followed for 20 weeks , with best-corrected visual acuity measured at enrollment , and at weeks 5 , 10 , 15 , and 20 after enrollment .