Many surgeons use the iris or pupil size as a guide for capsulorhexis creation — but you should not. Do not fall into this trap. Look at the picture above — both eyes have the same model lens with a diameter of 6.0 mm and both have a capsulorhexis which is about 5 mm in diameter, giving and excellent overlap of the optic. But the eyes are very different — the anterior segment size, the white-to-white measurement, and the pupil dilation are all markedly different. In the large myopic eye, using the iris as a guide would have resulted in an overly large capsulorhexis which would not have held the IOL optic securely. This is the reason why I use marks on my forceps.
At the beginning of the case, I hold the forceps to plan out the capsulorhexis size. The mark that is 2.5 mm from the tip should be placed in the center of the intended circular opening and then the 5.0 mm mark and the tip of the instrument outline the diameter of the ideal 5 mm capsulorhexis. With this image in my mind, I then create the capsulorhexis with these dimensions and position. At the end of the surgery we can see that the capsulorhexis is this desired size.
You do not need to purchase new forceps — you can simply make marks on your existing forceps or use another metered device such as a marked spatula. You could also spend a tremendous amount of money for a femtosecond laser or use another automated device to create this capsular opening, but I have faith in your skills. I know that even beginning surgeons can do it manually, with enough experience.
Click below to watch this technique of capsulorhexis creation: