Ideally, the capsulorhexis diameter should be slightly smaller than the optic diameter so that we can achieve 360° overlap. But what if it doesn’t? Well, it turns out that it is not that big of an issue because the capsule shrink-wraps in the post-op period and it makes the capsulorhexis diameter about 10% smaller — sometimes even more. Remember that the cataract is about 4 mm thick (like an M&M candy) while the IOL is as thin as a coin (1 mm thin). This means that the capsular bag will end up shrink-wrapping quite a bit in the post-operative period.
The typical amount of capsulorhexis diameter shrinkage is about 10% but this can vary. Cases of capsular phimosis are an example of shrinking many times more than typical, with the zonular structures being too weak to oppose the shrink-wrap forces.
In the case presented here, the capsulorhexis overlaps the optic in some areas, but not in others. Since the optic is 6 mm in diameter, this means that the capsulorhexis is slightly larger than 6 mm in some areas and then slightly smaller than 6 mm in others. Again, this is not a concern since the 10% shrinkage (or more) of the capsular bag will result in overlap of the optic and secure positioning for many years to come.
Click below to watch the video of a capsulorhexis that is slightly too large:
