Source AAN: http://journals.lww.com/neurotodayonline/Fulltext/2016/03030/Phenytoin_Appears_Neuroprotective_of_Retinal_Nerve.6.aspx
I am sure PHT has far more adverse effects on nervous system than just some questionable neuroprotective effect on retinal nerve. I would urge NIH to stop funding these type of studies which fail to add any meaningful benefit to society. Just a waste of time and money of society. Of course author will add one more publication to their list, which seems to be goal now a days for those working at academic centers.
Not sure why we even worry about studying one variable at a time anymore. Biological organisms are complex and there is interaction between multiple variables at every moment of time. This is the reason why one study says something and another study on same the variable says something exactly opposite. They failed to look at the interaction the between major variables and hence came to different conclusion. example: coffee consumption. We got to change the way we do research studies.