Well, the rendered image IS called "astigmatism.png". Maybe POV-ray's new
artificial-intelligence engine is at work, digesting your code and comparing it
to millions of human vision tests that it scraped for free from private medical
records around the world. Then it responded accordingly. Check your messages
pane, to see if the following is there:  "Hey, if this image looks blocky to
you, you definitely have astigmatism! Everyone else sees a perfectly normal
image."

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