Phenylephrine-induced anterior chamber hypoxia.

The effect of topical phenylephrine 10% solution on anterior chamber oxygen tension (PO2) was studied in cats using an oxygen-sensitive electrode inserted into the midanterior chamber. A decrease in anterior chamber PO2 was usually observed within eight to 25 minutes and declined steadily thereafter. Within two hours, the drug caused a dramatic 60% reduction in anterior chamber oxygen tension (P less than or equal to .0005). We suggest that the mechanism for this phenylephrine-induced anterior chamber hypoxia is reduced blood flow, mediated by the direct vasoconstrictive effect of the drug and compression of the iris vasculature (induced by dilatation). The resulting decrease in the caliber of the iris arteries produced a parallel decrease in blood volume and flow which resulted in diminished PO2. Phenylephrine 10% may contribute to hypoxia and exacerbate the underlying pathology in those disorders where hypoxia plays an important causal role.