We recently featured a four-part series of a single, complicated cataract case in which the phaco probe punctured the posterior capsule during nucleus removal, then the capsular bag collapsed during cortex removal, a toric IOL was placed in a damaged capsular bag, then it was explanted and an anterior vitrectomy was done prior to placing a three-piece sulcus IOL with optic capture.
When we changed the toric IOL for a spherical sulcus IOL, we actually increased the IOL power from +18.0 for the toric IOL to +19.5 for the spherical IOL. Why?
To change from the toric IOL (A-constant = 119.2) in the bag to the spherical IOL (A-constant = 118.7) in the bag, we would just subtract the two A-constants (119.2 – 118.7 = 0.5 D). Therefore we would drop the IOL power from +18.0 to +17.5 to get the same spherical equivalent refraction of plano.
But what about for sulcus IOL placement? We refer back to the Rule of Nines, and in this case we would further drop the IOL power by 0.5 to get a power of +17.0 for the same spherical equivalent of plano.
So why would we select an IOL power of +19.5 for this patient? Wouldn’t that result in a more myopic post-operative outcome? Yes, it would, and that is precisely why we are choosing it. Remember that we are no longer using a toric IOL and so we must make a plan to treat the residual astigmatism by other means.
- SN6AT5 +18.0 with +2.0 D of toric correction at the corneal plane. This would have resulted in a post-op refraction of 0.00 plano if we placed it into the capsular bag.
- MA60AC +17.5 without toric correction in the capsular bag. This IOL would give a post-op refraction of about -1.00 +2.00 x 75 (same as +1.00 -2.00 x 165), which is a spherical equivalent of plano
- MA60AC +17.0 without toric correction in the sulcus. This would have resulted in a post-op refraction of about -1.00 +2.00 x 75 (same as +1.00 -2.00 x 165), which is a spherical equivalent of plano
- MA60AC +19.5 without toric correction in the sulcus with optic capture. This will result in a post-op refraction of about -2.25 +2.00 x 75 (same as -0.25 -2.00 x 165), which is a spherical equivalent of -1.25 of myopia
After the cataract surgery heals, we will perform LASIK excimer laser ablation for the residual prescription. The excimer laser will not do as well with the mixed astigmatism prescriptions that have a spherical equivalent of plano. This is because the laser will have to steepen one meridian and then 90 degrees, away try to flatten the other. This was previously explained here.
A better result is for the laser to ablate a clean myopic cylinder. Notice how the +19.5 MA60AC gives a post-op result of -0.25 -2.00 x 165 which is a very clean and easy ablation for the laser. It is also very precise and we can give the patient a true final refraction of plano, just as desired.
The four videos in this series are linked below for your review:
Part 1: Failed chop and capsular puncture during phaco
Part 2: Collapse of the capsular bag during cortex removal
Part 3: Implanting and then explanting the Toric IOL
Part 4: Anterior Virtrectomy and Sulcus IOL Placement with Optic Capture
