We want a capsulorhexis to be just large enough to overlap the optic of the IOL in order to hold it securely in place. This also provides a more predictable effective lens position which is important in accurately determining the post-op refraction. If the capsulorhexis is too large then it will not provide sufficient support of the IOL, though there will be some contraction and shrink-wrap effect in the post-op healing period. if the capsulorhexis is too small then it will become more difficult to remove the cataract during surgery and there can be excessive contraction or even phimosis in the post-op period.
We can measure the capsulorhexis using our forceps during the manuever to ensure that it comes out the correct size. We can also start smaller and then spiral out the capsulorhexis to the desired size. We can even use some very fancy and very expensive equipment to do the capsulorhexis automatically.
Click below to watch the video and try your best to estimate the capsulorhexis size: