Which visual distortion could result as medieval lenses deviate from perfect spherical surfaces?

💡 Explanation

Coma arises when off-axis light rays focus at varying points due to uneven refraction; this is **spherical aberration** mechanism. Imperfect shaping of the lenses leads to coma formation because the focusing differs across the lens area, therefore off-axis points appear smeared out, rather than showing chromatic colour separation or uniform pin-cushion error.

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