Lactate dehydrogenase levels in tears were measured in normal subjects and in patients with retinoblastoma. When specimens were collected without trauma in normal subjects, there were usually no detectable levels of lactate dehydrogenase. When the eyelids were rubbed (probably liberating epithelial cells) lactate dehydrogenase levels were detectable and were five to ten times those of normal aqueous humor. When lactate dehydrogenase isoenzymes in such specimens were analyzed, the level of lactate dehydrogenase 5 was always higher than that of lactate dehydrogenase 1 (similar to normal aqueous humor). While occasional patients with retinoblastoma do have elevated levels of lactate dehydrogenase in tears, it is uncertain if this is due to epithelial destruction or retinoblastoma itself. Lactate dehydrogenase in tears does not appear to be a useful test for the diagnosis of retinoblastoma given present techniques for collection and analysis.
