This article is more than 5 years old. Information may no longer be current.
Extra effort needed to achieve ideal results in refractive cataract surgery patients
Click Here to Manage Email Alerts
The most demanding lens implant patient for me in regards to postoperative residual refractive error is the individual who has significant astigmatism and desires spectacle independent vision at all distances. While there are different surgeon preferences and lens implant approvals in each country, let’s presume we have access to and have chosen to use a bifocal or trifocal toric diffractive multifocal IOL.
My experience is that in order to achieve high patient satisfaction, I need to generate a refractive outcome with no more than 0.5 D of residual astigmatism and less than 0.5 D of residual spherical equivalent. There are many published series of refractive outcomes, including those from the United Kingdom, the Swedish registry and, closer to home, a large registry of cases accumulated by Guy Kezirian. These data sets suggest that with standard methods of optical biometry, astigmatism measurement and steeper meridian marking, the “typical surgeon” only achieves this outcome in 50% to 65% of cases.
A few thoughts on the challenges and some of the methods I have found helpful in improving my outcomes. In our practice, we use optical biometry whenever possible, which includes at least 95% of our patients. We will utilize immersion ultrasound biometry in cases in which we cannot get a reading with optical biometry. Optical biometry is very accurate and rarely the source of a meaningful postoperative refractive surprise. Measuring the mean keratometric power of the cornea, the magnitude of the astigmatism and the steeper meridian presents a much greater challenge. Each keratometer measures the corneal power at a different diameter, and all must be calibrated. Using a consistent method of keratometry and a consistent model of IOL and then collecting postoperative data to personalize one’s so-called A-constant can enhance outcomes.
Unfortunately, the patient with a history of corneal refractive surgery is a common challenge in my practice, and accurate measurement of the corneal power is especially difficult in these eyes. In addition, many of these patients have significant spherical aberration and coma; therefore, I rarely utilize a multifocal IOL for them. The ASCRS IOL calculator is an excellent tool in these patients, but one is still presented with a patient in whom residual refractive error is more common, and all my patients are counseled that they may need a postoperative refractive enhancement if they are highly motivated to have spectacle independence.
The steeper meridian is also a challenge. I measure several ways, using manual keratometry, the IOLMaster (Carl Zeiss Meditec), Humphrey or Tracy Placido disc topography, and the Pentacam (Oculus) or Orbscan (Bausch + Lomb). In addition, I look at the refraction. Unfortunately, in many patients, the steeper meridian varies significantly from one measurement to another. Clinician judgment is useful, but these variable measurements provide a challenge. My solution includes the use of intraoperative keratoscopy with a Mastel keratoscope and/or the Alcon WaveTec intraoperative aberrometer. My very best outcomes have been obtained through marking the steeper and flatter meridian before making my incisions with the Mastel keratoscope and then completing a final check with intraoperative aberrometry. This is, to be sure, a lot of work and requires two separate microscopes because there is no intraoperative aberrometer with a built-in surgical keratoscope.
Even with all this technology, my challenges are still significant. I do not personally have an instrument that reliably measures posterior corneal astigmatism, which can be significant. I rely on Doug Koch’s finding that the typical patient has against-the-rule posterior corneal astigmatism of about 0.3 D. This is convenient for me because my typical incision in the horizontal meridian flattens the cornea a similar amount. I therefore personally always do both my primary and secondary incision at the 180° meridian when treating astigmatism with a toric IOL. I assume these horizontal incisions will neutralize the posterior corneal astigmatism, but I know this is only a rough estimate and hope in the future to be able to measure it accurately.
To add to my challenge, while my mean surgically induced astigmatism might be 0.3 D at 1 to 3 months, there is a significant standard deviation, with some patients actually steepening and some flattening as much as 1 D. In addition, what I measure at 1 month after surgery is usually more than what I measure at 1 year. And sadly, even at a year, the outcome is not stable, with most corneas flattening and drifting against the rule 0.5 D to 1 D a decade. I can target for plano to slight hyperopia and a small amount of with-the-rule astigmatism, but different patients will change different amounts and at different rates as they age.
These are sobering facts and make me realize that some of my patients will require one or more enhancements as they age if they are to retain the best possible vision without correction for a lifetime. There are still more challenges, including the fact that a toric lens implant that is 10 D in spherical power with a labeled 1.5 D of toric power will correct significantly less astigmatism than one with 30 D of spherical power. I presume a 20 D toric IOL is accurately labeled but make adjustments when using a high- or low-powered toric IOL.
Finally, even with intraoperative keratoscopy and intraoperative aberrometry, I know that I will be at least a few degrees off the exact steeper meridian with my toric IOL. A toric IOL placed off axis will undercorrect the patient’s astigmatism. Thus, just as I do in my corneal refractive surgery patients with high astigmatism, I favor increasing the power of the toric IOL slightly because most patients are undercorrected if I simply plan the IOL on the actual keratometry readings.
Using careful preoperative biometry, intraoperative keratoscopy with marking combined with a final check with intraoperative aberrometry, I was recently able to evaluate a consecutive series of 25 eyes with preoperative refractive astigmatism between 1 D to 3 D. At 1 to 3 months postoperative, I achieved a residual refractive cylinder and spherical equivalent within 0.5 D of plano in 92% of the eyes, and the greatest outlier was less than 1 D. This is a similar outcome to that reported by others using intraoperative aberrometry, including the recent randomized prospective trial sponsored by Alcon before it acquired the WaveTec ORA, in which 89% of eyes were within 0.5 D of target vs. 76% in the control group.
My personal results with laser corneal refractive surgery approximate 95% within 0.5 D of emmetropia, so using a full-court press of technology, I am getting closer with my refractive cataract surgery patients, but it is a lot more work with many more variables to consider. On the positive side, combining my best effort during refractive cataract surgery with a postoperative laser corneal refractive enhancement or two, I can in almost all patients achieve an outcome within 0.5 D of target.
The next challenge is to work toward an outcome within 0.25 D of target, and of course I would also like to eliminate at least spherical aberration and coma. On top of that, my patients and I would prefer to do it without requiring a laser corneal refractive surgery enhancement. An adjustable IOL, especially one that can be adjusted several times as the patient ages, will likely be required to get where I want to be, but I have definitely made a lot of progress in the last decade, with more to come.
Disclosure: Lindstrom reports he is a consultant for Abbott Medical Optics, Alcon and Bausch + Lomb, and on the speakers bureau for Alcon.