'astigmatical' originates from New Latin/modern medical formations derived from Greek 'astigmatos', where 'a-' meant 'not' and 'stigma' meant 'a point or mark'.

'astigmatical' developed via New Latin/Medieval Latin terms such as 'astigmatismus' and the adjective 'astigmaticus' (used in medical/optical contexts) and eventually entered English as 'astigmatic' and the less common variant 'astigmatical'.

Initially it conveyed the literal sense 'not having a point' in reference to optical focus; over time it evolved into the specific medical/optical meaning 'relating to astigmatism' (i.e., producing blurred or distorted vision).