Eyes come in a spectrum of sizes, particularly with the measurements of the anterior segment in patients with extreme refractive errors. Patients who are very myopic with long axial lengths also tend to have larger anterior segments as measured by the white-to-white diameter. Most of our IOLs have optic diameters of 6 mm and this is why we aim for a 5 to 5.5 mm capsulorhexis for almost all patients. We get into a habit of using the pupil size to assist in making the proper sized capsulorhexis, but this may not be accurate in many eyes.
In this large, myopic eye the white-to-white diameter is 12.6 mm and the pupil dilation is 8 mm. We use the capsulorhexis forceps, which have marks the 2.5 mm and 5 mm from the tip, to measure as we create the capsular opening. There are other methods as well such as using marks on the cornea or employing a femtosecond laser. Note that I do not have a financial interest in the forceps which bear my name. You can use a disposable steel keratome to engrave similar marks on your existing forceps.
click below to see this technique and learn other pearls for highly myopic eyes: