I can honestly say that Sinemet has helped my DP/Dr A LOT. It still has a reducing effect on my afterimages as well. I never got much relief from visuals with Sinemet but Im not taking it for that. The DP/Dr aspect of this problem is the biggest issue for me and that's what Sinemet helps the most.
The only other thing that I can say for sure that drastically reduces both visuals, anxiety and DP/DR are opiates. The only problem is that they cause hardcore dependency. Sometimes I wonder if being addicted to opiates is a better life choice than having to constantly worry about HPPD on a daily basis.