In a manner relating to or characteristic of astigmatism; in the way that astigmatism affects vision.
From astigmatic plus -ally (adverbial suffix). This word is rarely used but exists in formal optical and medical discourse to describe how something relates to astigmatic vision.
Adding '-ally' to a medical term is how scientists describe 'in the way of that condition'—so 'astigmatically' means you're describing something through the lens (literally!) of astigmatic vision problems.
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