I want to preface that my symptoms are/were severe. Ranging from mild annoyances like visual snow, palinopsia, tinnitus, headaches, muscle twitching to severe problems like sicca dryness, mental disorientation, fatigue, chronic muscle tightness causing sharp pains, GI dysmotility and intestinal pseudo-obstruction. I basically developed a brutal form of HPPD.
After some recent GI-related problems, I was tested thoroughly by a doctor looking for answers. By stroke of luck, I tested positive for something that explains very well a large portion of my symptoms. I have positive antibodies for Ganglionic ACHr (acetylcholine) alpha-3 receptor. Here's a paper with more detail: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3764484/
I'm not really sure how many others here would test positive for the same receptor. It has been studied, and while very rare, does not accurately describe and represent HPPD-type symptoms of visual distortion (although I believe mood related problems are connected). But, what I realized for the first time is that it's not just a problem of receptors not functioning properly, but also my immune system is actively involved in the process of disrupting my neural communication.
Antibodies connect to the receptor and therefore block my ACHr from working properly. So, any discussion of my receptor malfunctioning is somewhat moot. The receptor is targeted by immune system to block its function. Fuck you immune system.
Don't know what this means yet, but while I'm still working to make connections to all sides, it does explain why Prednisone (immunosuppresive therapy) has been effective for me in the past.
EDIT: Don't know why I forgot, but the auto-antibody for acetylcholine actually DOES have implications on the visual system. As shown in the paper, people with this antibody has impaired reflexive pupils causing photophobia. Bingo.