To see it, we have take account of Strato's theory. In sum, he explains visual perception in terms of transmission of a quality, not a corpuscle. In doing so, Strato stays closer to Aristotle than Hieronymus does. Thus a possible interpretation of Hieronymus' fr. 53 W. can be summarized as what follows.
Sense perception occurs by way of corpuscles passing from the object to the sense.
The corpuscles are not homogeneous. These heavy parts are not flexible enough to get through our pores. An additional factor is our age. The more aged we are, the more inflexible our pores are too. They fit into our pores.