Feb 23, 2011
The baby boomers have loved having Lasik and PRK surgery for the past 16 years since initial FDA approval in the U.S. in 1995. I call the baby boomers the "I want it all and I want it now" generation so you could see how they would gravitate to the remarkably fast and accurate results of refractive surgery. Now many boomers are approaching their 60's and, not surprisingly, they are developing cataracts. Picking the best IOLs for these cataract surgery cases, however, is quite challenging and is an underappreciated science.
10 years ago I did cataract surgery after refractive surgery about once a year, but now it has increased to about twice a week. I have, necessarily, invested a great amount of time and money into the proper training and equipment in order to maximize the results. You see, picking the proper IOL for these cases is fraught with possible errors. The excimer laser used in Lasik and PRK creates changes in the curvature of the cornea, sometimes major, sometimes sublte. But the changes are not what you would see in a typical human eye. In a very basic way, I tell patients that the new cornea takes on a slightly non-human shape and thus the typical devices and mathematical formulas used to pick IOLs for cataract surgery will usually give innacurate results.
The solution is to use a corneal mapping device such as a Zeiss Atlas Corneal Topography system. This system can pick up the subltle changes in curvature and give average corneal power readings at different optical zones. Importantly, the results from the Atlas can be entered into the ASCRS Post-Refractive IOL Calculator computer application. This is a critical step that cannot be overlooked, in my opinoin. The Atlas also measures corneal spherical aberration which can be hugely affected by previous Lasik or PRK surgery. Some of the most expensive apheric IOLs such as the Tecnis or Acrysof may need to be avoided in patients with high levels of negative spherical aberration - namely those who have had hyperopic Lasik or PRK. On the other hand, patients with with previous myopic Lasik or PRK often have high levels of positive spherical aberration and can benefit greatly from an aspheric IOL.
One more thing that is commonly overlooked is knowing whether myopic or hyperopic lasik was done and, in my experience, most patients don't have a clue. Old records are helpful but are usually unavailable. Some properly worded questions about their visual history will usually help. Completely different IOL mathematical formulas are used depending on the type of previous Lasik/PRK treatment. The good news is that the Zeiss Atlas has a program which can usually tell you what type of surgery was done. Another good reason to choose that machine.
In the end, four things are crucial: 1. Determine whether the patient had myopic or hyperopic Lasik/PRK surgery. 2. Accurately measure corneal power with a very good corneal topographer. 3. Measure corneal spherical aberration and pick IOL model accordingly. 4. Use the ASCRS Post-Refractive IOL Calculator to pick IOL power. accordingly.
Don't hesitate to post questions if you have them. This is one situation where it pays to be obsessive-compulsive. Little things can make a big difference!