An average eye has an axial length of about 23 to 24 mm, but this patient had an axial length of about 40 mm. This extreme axial length induced a huge amount of myopia and it makes the cataract surgery far more challenging with greater risks. These include inaccuracies in the IOL power estimation and the risk of a retinal detachment in the post-op period and then in the years to come. It is critical that these patients have a very thorough retinal examination before cataract surgery.
My preference is to refer these extreme axial myopes to my vitreo-retinal colleagues who will then perform a detailed posterior segment examination and prophylactically treat any notable areas of retinal periphery weakness. After cataract surgery, I send the patient back to the retinologist for another detailed follow-up exam and then lifelong follow-up.
For the IOL power estimation (and it is just an estimation, not a precise calculation in these patients), the key is to aim for residual myopia. As we have shown before, do not aim for plano in ultra myopic eyes. In this case we are aiming for about -3 to -4 diopters for the post-op refraction. We are determining the estimated IOL power using these methods.
In the USA, the most extreme IOL power available for these eyes is a -10 diopter, three-piece, acrylic IOL. In this patient, using this most extreme -10 D IOL, the predicted post-op spherical equivalent is determined to be -3.5 which is what we desire. Do not attempt a piggybacking of IOLs in these eyes if your calculations call for a more extreme IOL power than -10 D. Going from -39 diopters of myopia to a refraction of -3.5 diopters is a great result. But going from -39 to +2 is not good because these patients simply do not tolerate hyperopia well.
We use multiple important maneuvers in this case:
- measure the capsulorhexis before performing it to achieve a 5 mm diameter
- avoid anterior chamber collapse during the surgery to prevent barotrauma from pressure fluctuations
- be weary of abnormalities in other tissues such as a thin capsular membrane, a thin/unusual cornea, and zonular laxity
Click below to see the most extremely myopic patient that I’ve encountered in 20+ years: