Our ideal capsulorhexis will overlap the optic edge for 360 degrees in order to hold the IOL securely in a predictable position to ensure refractive accuracy. We can use forceps with marks on the tips to accurately measure this size during the procedure. While we usually aim for a capsulorhexis with a diameter of 5 to 5.5 mm, there are times when we want something different.
A larger capsulorhexis is helpful in cases of a very dense cataract with a fibrous posterior plate because it will allow us to get the nucleus out of the capsular bag and place the chopper behind this area. We may also want a larger capsulorhexis in cases where there may be future anterior capsular phimosis such as in pseduo-exfoliation syndrome and retinitis pigmentosa. Here a 5.5 or even 6 mm capsulorhexis would be great.
A smaller capsulorhexis is helpful in cases where there are other concomitant surgeries and we want to ensure that the IOL does not come out of the capsular bag even if the anterior chamber shallows or there is an air bubble in the eye. These include glaucoma surgeries, pars plana vitrectomies, and even corneal surgeries. Here a 4.5 to 5 mm capsulorhexis may be advisable.
Click below to see if your mental calipers are accurate for judging capsulorhexis size: