wouldnt a direct injection into the eye do nothing but cause blindness? (and an unsafe change in intraocular pressure?)
to get something into the visual processing center, you would need to go through the back of the skull. If we consider that the drug migrates through diffusion, wouldn't it impact the olfactory bulb first, due to proximity?
Kids these days...
If you wanted drugs to freely circulate around the brain, the best way would be to contaminate the cerebral spinal fluid, then have them take a nap.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4016637/https://www.nih.gov/news-events/nih-research-matters/how-sleep-clears-brainSome drugs can cross the blood-brain barrier. Others can cross as a result of purposeful irritation/injury to arterial walls in the brain.
https://www.ncbi.nlm.nih.gov/pubmed/26486344SO--
You have a few options that are realistic.
1) This envenomating actor does it directly through the skull, to contaminate the CSF
2) It envenomates you through the bloodstream, then projects high intensity sound at you so that its venom can get into your brain.
Either one would be adequate. Both are likely to do you some serious collateral along with it
enjoy.
However, for the sake of argument----
Let's assume that the optic nerve bundle is able to diffuse CSF efficiently and rapidly. (which it doesn't. It's a downstream tributary of that circulation network.) First, it would pass through the hypothalamus, then the thalamus, THEN it would reach the visual cortex. See these handy anatomical charts.
The thalamus and hypothalamus are associated with sensory integration, and the processing of sensory signals into sensory perception, as well as the encoding and recovery of memories, and the regulation of the limbic system.
https://medicalartlibrary.com/thalamus-hypothalamus/SO-- if we took the concensus of your group at face value-- that a pathogen can interact with the brain via diffusion through the optic nerve and optic chasm spaces, it would not make you see things. It would make you very confused, agitated, and likely make it hard for you to breathe, swallow, stand, and a number of other functions associated with sensory integration with the cerebellum and spinal cord-- LONG before it reached your visual center.