I'm getting quite a bit closer to fusion with the help of my seven diopter prism.
I started using it out of frustration, because I'd been doing the same regimen for about two months, and it seemed like I would be able to, in time, get accommodation synchronized across the eyes with the fixation card exercise. But I stopped making progress. Since accommodation and eye angle are linked, I figured I might be able to coax equal eye accommodation via a prism. So that's what I did. I started using a seven diopter prism base in. This enabled me to get both double images very close to being in sync--both in terms of fusion and accommodation.
It seemed to free up some energy, and while I don't yet have fusion, it has brought me very close to fusion. The targets are almost a single fused target at times. The prism has brought fusion into much closer and more realizable reach. There are times where I was sure that I had fusion, briefly.
Interestingly, it hasn't hurt my ability to diverge my eyes. I would have thought it might because my using the prism I'm sort of conceding to my eye's esotropic tendencies, and rendering it even lazier in terms of divergence. But that doesn't appear to be a problem. In fact, the Brock String exercise has improved quite a bit since I incorporated the prism in the fixation card exercise.
The rationale is to really practice fusion and teach my brain that this is what it wants. And then to reduce the prism. But somehow I doubt that that will be the big part. I think the big part will be achieving fusion. In all my years I never had it. I think my eye's laziness was such an ingrained habit that in all of my years of vision therapy no amount of coaxing would enable me to truly get both eyes working together. I'd used prisms before. But now they seem to be working. Or I had finally started making sense of what I'm doing with prisms.