Astigmia

[…] and the measurement and correction of astigmia is one of the chief functions of the optometrist.

Astigmia of the whole eye […] is the resultant of the special astigmia of all four refracting surfaces, […]

Regular astigmia must be considered congenital, as a rule.

When the corneal astigmia is direct, and about 0.75 D., we may expect to find an almost total absence of astigmia by subjective examination.