It appears well established that tobaccoalcohol amblyopia has a nutritional rather than a toxic etiology.1,2 As yet, the metabolic aberration or specific vitamin deficiency responsible for the development of this syndrome has not been defined. A lack of cyanocobalamine (vitamin B12)3, thiamine,4 riboflavin,5 and pyridoxine6 has been implicated in the genesis of amblyopia. Except for low serum cyanocobalamine levels and an abnormal urinary excretion of methylmalonic acid,7 no other biochemical abnormalities have been reported in instances of tobacco-alcohol or deficiency amblyopia. Recently, whole blood transketolase assays, which reflect in a sensitive and specific manner the state of thiamine nutrition, have been performed in two alcoholic patients suffering from untreated amblyopia. The results of these assays clearly demonstrate that a deficiency of thiamine is present in some cases of amblyopia.
Transketolase, a thiamine dependent transferase, acts as catalyst in the metabolic step which condenses