We appreciate the thoughtful comments of Dr Hesse regarding
adverse effects of intravitreal commercial tPA solution on the retina.
It is reasonable to assume that the larger volume of the human vitreous
should raise the threshold for tPA toxicity compared with the cat eye.
However, we have shown that the larger volume of the cat vitreous
cavity compared with that of the rabbit does not increase the margin of
safety for intravitreal tPA.1,2 This fact, together with the geographic distribution of toxic changes around the injection site,
suggests that tPA is not diluted evenly throughout the vitreous cavity.
Extrapolations of safe doses based on vitreous volume may therefore be
Johnson MW. Intravitreal Injection of Tissue Plasminogen Activator: Four Considerations. Arch Ophthalmol. 2001;119(3):456-457. doi: