Calculating Bag vs. Sulcus IOL Power.
If during cataract surgery, the decision is made to place the
intraocular lens in the ciliary sulcus, rather than the capsular
bag, a decrease in lens power is often necessary. This is due to
the fact that as the optic is shifted more anterior (moved closer
to the cornea), its "effective power" increases. The amount of this change is dependent on the "base power" of
the intraocular lens. The greater the power, the greater the difference.
Below is a chart for which this calculation has been made over
a standard range of base powers from +30.00 D to +5.00 D. The central
corneal power is assumed to be in the normal range. The capsular
bag effective lens position (aka: ACD) is assumed to be 5.20 mm
(as with the popular Alcon MA60AC), but these numbers will work
with almost any modern posterior chamber intraocular lens. The
effective lens position for the ciliary sulcus is estimated to
be 4.70 mm.
It is recommended that this information be available in the operating
room as a handy reference for whenever this situation arises.
