The Rule of 9

Sulcus IOL Power Adjustment

<9 D	No change
9 – 17 D	Reduce by 0.5 D
18 – 26 D	Reduce by 1.0 D
≥ 27 D	Reduce by 1.5 D

When placing an IOL in the sulcus instead of the capsular bag, the more anterior position (~0.5 mm) shifts the focal point forward, resulting in a myopic surprise. Higher power IOLs are more sensitive to this positional change because the relationship between power and positional effect is nonlinear.

Source & credit: This rule was invented by the cataractcoach @uday.devgan. Check out his website cataractcoach.com and his YouTube channel @UdayDevgan for a ton of useful tricks in cataract surgery.