BLOG: Using lens meridian position as a tiebreaker: A case example
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Key takeaways:
- Lens meridian position can help guide surgical planning.
- Lens meridian position may have a role in improving estimation of effective lens position.
A firefighter in his early 50s presented with early subcapsular cataracts.
As a relatively high hyperope (+3 D) with mild astigmatism and little residual accommodation remaining, he was struggling to perform in his job with progressive spectacles. Contact lenses weren’t an option given the smoky environments he was exposed to, and he wasn’t a good candidate for LASIK, either.
We proceeded with preoperative biometry measurements from the IOLMaster (Zeiss) and the Aladdin biometer/topographer (Topcon). I’m always looking for consistency in the keratometry and IOL power calculations from different devices and different formulas. In this case, the Barrett formula recommended a 21 D lens, and the Holladay 2 recommended a 20.5 D lens. The predicted refraction with a 21 D lens was –0.15 D with the Barrett II and –0.5 D with the Holladay 2 (Figure 1). The patient did not have ocular surface disease or any other pathology other than cataracts.
The options
The simplest option in such a case would be to just choose the first minus power with one of the formulas and hope that biometry was accurate. With the Tecnis Symfony extended depth of focus (EDOF) lens (Johnson & Johnson Vision) I planned to implant, the patient would have good distance vision even if he ended up a little myopic. However, I really wanted to achieve the best possible distance vision and a nice range of vision for this patient, rather than using the EDOF range to compensate for residual myopia.
Another option would be to use ORA intraoperative aberrometry (Alcon) to make a determination in the OR of which lens to choose. However, in my experience, intraoperative aberrometry hasn’t provided consistent enough results when I’m trying to choose between two lens powers, perhaps because it does not factor in effective lens position (ELP). Its calculations are also stratified based on the preoperative data that are entered.
The third option, which is what I did, was to order both lens powers for the day of surgery and make the decision based on intraoperative OCT imaging from the Catalys femtosecond laser (Johnson & Johnson Vision). This type of imaging is the only way to gain visual insight of the fornix of the capsular bag. With cases like this, I make a note on the chart to check the lens meridian position (LMP) intraoperatively. LMP is the distance from the center of the anterior cornea to the equatorial plane of the crystalline lens. It has a positive correlation with anterior chamber depth but no real relationship to axial length or age. George Waring IV, MD, and colleagues have previously suggested that it may have a potential role in improving estimation of ELP.
After more than 3,000 cases performed with this femtosecond laser, when there is a small discrepancy between formulae, my personal nomogram is that if LMP is less than 5, I choose the lower power lens because I expect that it will likely sit more anteriorly in the capsular bag. If the LMP is 5 or greater, I choose the higher IOL power because I expect the lens to sit further back in the capsular bag.
This firefighter’s LMP was 4.5 (Figure 2), so I chose the 20.5 D lens. He was thrilled with his plano outcome, seeing 20/20 at distance, and still had good near vision of J2.
While newer power calculation formulas have improved their efforts to estimate ELP over the years, I find it more powerful to see the fornix of the capsular bag on OCT imaging myself and to look at the LMP to help guide my surgical planning. Using LMP is not necessary for every case, but as a tiebreaker when preoperative measurements are inconsistent, it can improve accuracy in the 10% or so of cases that would otherwise not have a satisfactory outcome. This is especially important when implanting an IOL with a refractive goal or in a young, active patient like this one, where guessing between IOL powers just isn’t good enough.
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