Hidden Threats to IOL Satisfaction

Beware the effects of spherical aberration and angle kappa on IOL selection.

Mitchell A. Jackson, MD

Patients that undergo cataract surgery in this modern age of combination refractive-cataract procedures have very high expectations. As we've all learned, the glasses Rx fix for visual disturbances postoperatively is no longer enough to maintain patient satisfaction and future word-ofmouth referrals. In the complex decision process for both the surgeon and patient on whether femtolaser technology, intraoperative wavefront aberrometry, and/or advanced IOL technology are all needed to achieve the best visual outcome, other factors are often neglected as part of the initial diagnostic workup. However, I find that these are just as critical to achieving the perfect image quality postoperatively. Post-refractive surgery patients bring even higher expectations for their outcomes. And if managing expectations, astigmatism, posterior capsule opacification, and avoiding cystoid macular edema are not already a menace to the surgeon for his/her patient, then beware of pupil size, spherical aberration, and angle kappa in your quest for the perfect outcome. These last may not be as well known as the other threats, but they can certainly sink your case. Here is what I have learned about navigating past them to success.

More About Those “Little Threats”

Spherical aberration (SA) is simply an aperture error where abaxial rays outside the central five-degree optical axis will be refracted stronger, causing visual image quality distortion. Traditional positive spherical aberration IOLs typically have a power increase from the center of the IOL to the edge. Aberration-free IOLs, in contrast, have a uniform diopter power throughout the entire IOL, and negative spherical aberration IOLs have a power decrease from the center of the IOL to the edge. Larger pupils will create more distortion through a spherical versus aspherical lens. This is in contrast to small pupils, which show no difference in image qualities (Figure 1).

Figure 1. Effect of pupil size on image quality

Image quality at a certain focal point typically will be best in negative SA IOLs, but depth of field is best with positive SA IOLs (Figures 2, 3). Usually, zero SA IOLs are the best happy medium in terms of image quality and depth of field. Angle kappa, or the mean displacement between the visual (foveal) and pupillary (optical) axes, is measured normally as 2-5 degrees in the horizontal axis, or as 0.36 mm (+/− 0.22) from an average of 18 studies.¹ Devices such as the Marco OPDIII and Hoya iTrace can measure scotopic/mesopic pupil and angle kappa in terms of degrees or mm and are very useful diagnostic tools in the IOL decision process (Figure 4). My practice utilizes the Marco OPDIII and it captures wavefront data measured to 9.5 mm, blue light corneal topography data (placedo disk 33 rings), lenticular astigmatism details, pupil size, spherical aberration, and angle kappa in just 10 seconds per eye measurement time — all of which are very useful preoperative data with no additional chair time.

Figure 2. Image quality effect with IOLs

Figure 3. Depth of field effect with IOLs

Figure 4. Marco OPDIII angle kappa measurement

The Key to Improving Patient Satisfaction?

One of the main complaints in patient dissatisfaction analysis of multifocal IOL technology is persistent glare and halo in low-light and night-driving conditions.² In my recent retrospective review of 40 eyes with prior myopic LASIK greater than 1 year postop that underwent uncomplicated phacoemulsification with IOL implantation (20 with Bausch + Lomb's Crystalens AO and 20 with AMO's Tecnis Multifocal), angle kappa was measured with the Marco OPDIII at a three-month minimum postop exam. None of these patients had angle kappa measured preoperatively as this was a retrospective postoperative review only. All IOL calculations were performed preoperatively with the IOLMaster 500 using Haigis-L software for preop myopic LASIK.

As presented at the recent SOI/OSN/AICCER meeting in Milan (May, 2012), statistical analysis revealed that all eyes were within +/− 0.50 D SEQ without any clinically significant PCO, CME, or corneal astigmatism. All patients were given a patient satisfaction questionnaire at a minimum of three months postoperatively, grading their ability to drive at night and in low light conditions, to read small print and restaurant menus in dim light, and their experience of glare and halos around lights. Results of the patient satisfaction surveys showed similar satisfaction responses no matter how large the angle kappa measurement in Crystalens AO patients, but higher satisfaction if angle kappa was less than or equal to 0.4 mm in Tecnis Multifocal patients.

Even in the monofocal IOL arena, there are differences in IOL asphericity based on the lens model/manufacturer (Figure 5) that may impact IOL selection, especially in postrefractive surgery patients. Prior hyperopic LASIK normally will induce negative spherical aberration postoperatively, whereas myopic LASIK will cause positive spherical aberration postoperatively. In a prospective cataract patient it is important to cancel out or minimize any further spherical aberration with placement of the new IOL. As seen in Figure 6, the IOL selection decision for a prospective cataract patient can be simplified and customized based on angle kappa measurement preoperatively. Certain monofocal IOLs such as the Hoya FY-60AD, even have an additional benefit of a “super prolate” aspheric negative SA optic to adjust for both high angle kappa and positive spherical aberration.³ Devices such as the Marco OPDIII and Hoya iTrace will give actual spherical aberration measurements in addition to angle kappa readings to aid in the IOL decision process for a patient with or without prior refractive surgery, or post-LASIK.

Figure 5. IOL asphericity chart

Figure 6. Decision Tree of IOL selection

Keep Angle Kappa in Mind

In conclusion, spherical aberration is one of the bad guys in obtaining perfect image quality after cataract surgery. Angle kappa may have clinical impact in selection of accommodating versus multifocal IOL technology in patients with or without prior corneal refractive surgery. Once the surgeon addresses patient expectations, astigmatism, PCO and macular pathology in a dissatisfied patient, it is time to look at angle kappa in terms of IOL selection as a possible determinant of the poor visual outcome. The risk of possible future multifocal explantation in a dissatisfied patient may be avoided with use of devices such as the Marco OPDIII and Hoya iTrace to measure angle kappa and spherical aberration preoperatively.

In my opinion, with an angle kappa of 0.40 mm or less, multifocal technology should be a safe bet, excluding preoperative macular pathology. For any angle kappa greater than 0.40 mm, multifocal technology should be avoided to achieve higher patient satisfaction, and even tailoring monofocal IOL selection becomes important in these patients. OM

References

1. Rynders M, Lidkea B, Chisolm W, Thibos LN. Mean displacement between foveal axis and center of pupil of 0.37mm + 0.24mm. J Opt Soc Am A 1995; 12:2348-2357.
2. Prakash G, Prakash DR, Agarwal A, et al. Predictive factor and kappa angle analysis for visual satisfactions in patients with multifocal IOL implantation. Eye 2011;25:1187-1193.
3. Baumeister M, Neidhardt, Strobel J, Kohnen T. Tilt and decentration of threepiece foldable high refractive silicone and hydrophobic acrylic intraocular lenses with 6-mm optics in an intraindividual comparison. Am J Ophthalmol 2005; 140(6): 1051-1058.

Dr. Jackson is in private practice in Lake Villa, III. He receives speaking fees from Bausch & Lomb, Abbott Medical Optics, Marco Technologies and Hoya.