What ratio of cannabis oil would be helpful for macular degeneration. Possibly THCA?

I don't believe there is any medical cannabis formulation that has been demonstrated to have a clinical effect on macular degeneration. Because cannabinoids have been shown in the laboratory to have "neuroprotective" biochemical attributes many people with neurodegenerative conditions, like macular degeneration, feel it is worth trying medical cannabis, given its low or non-existent toxicity. The difference between laboratory studies and clinical studies is a big one, and I am not aware of any published data showing medicinal cannabis effective in actually slowing or reversing macular degeneration. THCa, the biochemical precurser to THC, is felt by some people to have particular attributes, but I don't know how that is relevant here. THCa taken orally will be decarboxylated by gastric acid, and likely by heating also if it is vaporized for inhalation. I'm not clear why you think a THCa preparation might present some particular benefit for macular degeneration. I'd be more inclined to focus on CBD, not psychoactive and almost universally well tolerated.