Abstract

Purpose- The Centroid SIA measured by SIA calculators is lesser in magnitude, misleading & controversial.
Old SIA Calculator are based on vector method can measure magnitude (mean SIA & Centroid SIA) only. But can't measure rotation of steep axis which is also equally important to determine toric lens axis of alignment. New SIA calculator based on polar method can measure both component of SIA.

Method- Two groups are compared by using both calculators.
Group 1- 57 cases of 2.8 mm phaco incision & 2.8 mm OCCI on steep axis.
Group 2- 12 cases of 2.8 mm temporal phaco incision not on steep axis.
Centroid & mean SIA is calculate by using both calculators.

Results- Vector method provides only magnitude of centroid SIA.
Polar method provides us magnitude components of SIA as well as SIA component for rotation of steep axis.
In Group 1 magnitude components was 90 percent & in Group 2 rotation components was 90 percent.

Conclusion- Polar method measure SIA better than vector method.

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