Simulating defects with ray tracing software

Are there any free/open source ray tracing apps that can be tweaked to render a scene with some number of diopters of uncorrected cylinder error, to objectively simulate and illustrate the difference that amount of error actually makes?

Why: I went to an optometrist last week, had a full exam, then ended up having an argument about whether my prescription was "worth" correcting with Shaw lenses, or even freeform lenses.

The autorefractor's opinion:

right = +0.50sph, -1.25cyl x010 left = +1.00sph, -1.00cyl x162

His opinion:

right = +0.25sph, -0.75cyl x010 left = +0.25sph, -0.75cyl x145

The optometrist was adamant that I don't "need" Shaw lenses.

I pointed out that my cylinder strength was 0.25 to 0.50 diopters less than the autorefractor's report.

He said it was a necessary compromise in order to preserve binocular balance.

I countered that with Shaw lenses, no such compromise is necessary. I could have my cake & eat it too.

He got irate, and tried to convince me that 0.25 to 0.50 diopters of uncorrected cylinder strength is "no big deal".

I politely begged to differ, then raised the issue of adaptation (no adaptation with Shaw, vs at least some adaptation with regular lenses), geometric error with conventional lenses vs no geometric error with atoric-design freeform lenses, and basically made it clear that I didn't care whether I "needed" Shaw lenses… I wanted them, just like someone who wants a Tesla Roadster isn't going to be happy with a Mustang.

I told him that if he thought some other freeform lens design, like Zeiss 3D, is objectively superior to Shaw, he was welcome to try and talk me into it. Instead, he tried to pivot me to considering progressive lenses.

Yeah, that's right… he wouldn't let me get freeform single-vision lenses, but he would have happily sold me freeform progressive lenses. I told him, "HELL no!" I will never voluntarily subject myself to the geometry-mangling hell of progressive lenses.

I did mention that if he can somehow get his hands on Mitsui TouchFocus glasses, I'd definitely consider them (even if they're neither freeform nor atoric). But I know they're currently only available in Japan 🙁

I decided to not buy new glasses that day, and went home pissed and frustrated.

In retrospect, I think I figured out why he was so resistant to letting me have Shaw lenses. I can't prove it, but I'm pretty sure he doesn't actually have the hardware necessary to get the dynamic vergence measurements required for optimal Shaw lenses (now, assuming he ever did), and he knew I was going to notice and scream if he tried ordering them using static default values.

I found another optometrist I think might finally be able to give me what I think I want (next in line is someone whose practice explicitly includes kids with amblyopia, so I think I can safely assume he has the necessary gear to take Shaw's motor fusion measurements), but before I go and pay for yet another exam, I'd like to see for myself (via raytracing) just how big of a difference 0.25-0.50 diopters of uncorrected cylinder error objectively makes.

I'm cynical, but I'm willing to consider the possibility that 0.25 diopters of error might genuinely be less than I can notice (even in intentional, side-by-side benchmark-style tests involving 6-point sans-serif black-on-white text on a 518ppi 6.3" 2560×1440 display held 14" from my face, with appropriate spherical add to compensate for presbyopia if necessary). But I want to see the difference, or at least a reasonable simulation of it, and make that value judgment for myself.

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