We are fortunate to have a broad range of IOL options in Europe, including many types of presbyopia-correcting IOLs. In this somewhat crowded field, properly evaluating new lenses and deciding which one is best suited for an individual patient can be challenging.

With few exceptions, today’s manufacturers produce IOLs from high-quality materials that allow the creation of edge designs that protect against epithelial cell migration. Some design features have become so broadly available that they no longer play a crucial role in our decision-making, like the 360° square-edge design of most posterior chamber IOLs. Haptic design, however, remains an important criterion for toric IOLs because of the haptics’ role in rotational stability.

ADOPTING PRESBYOPIA-CORRECTING IOLs

We have a preference for premium lenses (eg, multifocal, trifocal, toric) based on IOL platforms that are known to us already. If the basic lens model performs well, then the premium model will also usually perform well. Beyond this, we look primarily at two factors in deciding whether to adopt a new presbyopia-correcting IOL: optical quality parameters and performance of the IOL at various distances and lighting conditions.

Optical quality parameters. At our center in Heidelberg, Germany, we have access to optical bench testing equipment. Using validated eye models, optical bench testing can predict the optical performance or sharpness of images viewed through an IOL at any distance, from a few centimeters to optical infinity, at different pupil sizes. The better the initial optical performance of an IOL, the more degradation of image quality a patient can tolerate before needing spectacles. An IOL with high-quality vision will also perform better across a wider range of defocus and may be more forgiving of mild residual refractive error or decentration. For example, the higher the modulation transfer function (MTF) value, the more contrast is transferred to the image, resulting in greater contrast sensitivity.

Optical bench testing also helps to characterize the optical aberrations inherent to any lens material, which affect the quality and range of vision that is possible with an IOL made from that material. For example, we are realizing the importance of chromatic aberration (CA), which occurs when individual wavelengths of light are out of focus, causing blur and reduced contrast sensitivity. The average eye has approximately 2.00 D of longitudinal CA between 400 and 700 nm and 0.80 D between 500 and 640 nm.¹ Achromatic IOL technology (ie, materials with a high Abbe number) can correct longitudinal CA and, especially when combined with correction of spherical aberration, enhance retinal image quality without negatively affecting depth of focus (Figure 1).^2,3

Figure 1. Achromatic IOL technology (right) can correct longitudinal chromatic aberration.

Clinical performance. Data on an IOL’s performance on the optical bench can be complemented by data on that IOL’s clinical performance at various distances and lighting levels and its ability to meet a given patient’s visual demands.

We take great care in evaluating patients’ typical reading distances. We seat patients at a computer and ask them to place the monitor where it would be in their home or office, and we have them hold a book or handheld electronic device to measure their reading distance. Through questionnaires and patient history forms, we also determine how much time they spend at different visual distances for work, hobbies, and daily activities.

It is not uncommon today for so-called near vision tasks to be at what we would in the past have considered an intermediate distance. For example, patients may be working on a laptop or using a tablet or smart phone at 60 cm instead of holding a book at 30 to 40 cm. We see this reflected in the growing popularity of low-add multifocal IOLs, with add powers of 1.50 to 2.75 D instead of the traditional 3.00 to 4.00 D.

We also want to know about halos and glare. In patients who drive at night or have high retinal function, and will therefore be more likely bothered by photic phenomena, choosing a lens with less risk of these side effects may take precedence over all other considerations.

Pupil independence is another important factor to consider in matching the IOL to the patient. Someone who expects spectacle independence but works in low lighting conditions, for example, is likely to be dissatisfied with a pupil-dependent IOL.

Pupil independence is a function of optics and lens material, not necessarily lens design. Diffractive multifocal, trifocal, and extended range of vision IOLs can be either pupil-dependent, as with the AcrySof Restor (Alcon) and Hoya’s extended depth of focus IOL (Gemetric), or pupil-independent, as with the Tecnis Multifocal (Abbott Medical Optics) and the AT LISA tri (Carl Zeiss Meditec) IOLs. Some pupil-dependent lenses reduce glare and halos, which is a positive characteristic for sharp distance vision at night; however, the tradeoff is that these lenses sacrifice near acuity in dim light.

All of these issues must be factored into the selection of an IOL that will best suit the patient. A pupil-dependent IOL that provides crisp distance vision and minimal night vision disturbances may be a good choice for a nighttime taxi driver but not for a mechanical engineer who wants to be spectacle-free while working in a poorly illuminated facility.

PUTTING IT ALL TOGETHER

We recently had the opportunity to evaluate the Tecnis Symfony IOL (Abbott Medical Optics; Figure 2), the first lens to rely on an echelette design for an elongated depth of focus, resulting in an extended range of vision. In essence, instead of splitting light into two or three focal points, the IOL spreads the focal point wider, so that there is a clear image over a range of vision. Defocus curves for this IOL depict an extended range rather than distance and near peaks; however, the tradeoff is some loss of acuity in the very near range. (Editor’s Note: Several other IOL technologies dedicated to extending depth of focus are described in detail in the accompanying sidebars.)

Figure 2. The echelette design of the Tecnis Symfony provides an elongated depth of focus, resulting in an extended range of vision.

Current studies have shown a clinically significant increase in range of vision with the Tecnis Symfony compared with the Tecnis monofocal (ZCB00). A sustained mean BCVA of 20/20 or better was reported through 1.50 D of defocus with the Symfony, with a 1.00 D increase in the range of vision throughout the defocus curve.⁴

The optic material of this lens corrects for both spherical and chromatic aberration, correcting for at least 0.75 D of lateral CA compared with the phakic eye and providing a high-quality retinal image. Like the other IOLs on the Tecnis platform, the Symfony is pupil-independent, with little degradation of near and intermediate acuity in dim light. The echelette design reduces the incidence of glare and halos to monofocal IOL levels.⁵

CONCLUSION

In our practice, the Tecnis Symfony lens will likely be a good choice for patients who want excellent UCVA for distance and intermediate-near tasks and those with high retinal function or night driving demands who would be bothered by glare and halos. Patients who do not need good vision in dim light, have heavy true near visual demands, and do not want to wear reading glasses even for fine print might be better served by a multifocal IOL. With the availability of more presbyopic IOL designs, surgeons should be aware of the performance characteristics of different lens features in order to truly customize lens selection for each patient.

1. Nagata T, Kubota S, Watanabe I, Aoshima S. Chromatic aberration in pseudophakic eyes. Nihon Ganka Gakkai Zasshi. 1999;103(3):237-242.

2. Weeber HA, Piers PA. Theoretical performance of intraocular lenses correcting both spherical and chromatic aberration. J Refract Surg. 2012;28(1):48-52.

3. Artal P, Manzanera S, Piers P, Weeber H. Visual effect of the combined correction of spherical and longitudinal chromatic aberrations. Opt Express. 2010;18(2):1637-1648.

4. 166, Data on File. Extended Range of Vision IOL 3-Month Study Results (NZ).

5. Auffarth GU. Clinical experience with an extended range of vision 1-Piece IOL. Paper presented at: the XXXII Congress of the ESCRS; September 13-17, 2014; London.

Gerd U. Auffarth, MD, PhD
- Chairman of the Department of Ophthalmology, University of Heidelberg, Germany
- Director of the International Vision Correction Research Center & David J. Apple Laboratory for Ocular Pathology, Heidelberg, Germany
- auffarthg@aol.com
- Financial disclosure: Consultant, Travel grants and lecture fees (Abbott Medical Optics)

Florian T.A. Kretz, MD
- Senior Research Specialist, International Vision Correction Research Center & David J. Apple Laboratory for Ocular Pathology, Heidelberg, Germany
- mail@florian-kretz.de
- Financial disclosure: Consultant, Travel grants and lecture fees (Abbott Medical Optics)