Multifocal Intraocular Lenses

Introduction

Multifocal intraocular lenses (IOLs) are designed to address both aphakia that is surgically induced during cataract surgery and the loss of accommodation that accompanies the use of monofocal IOLs. When inserted at the time of cataract surgery, monofocal IOLs offer the potential for independence from corrective spectacles or contact lenses. Currently, after cataract surgery, patients are resigned to the of use corrective lenses for accurate visual acuity (VA) at more than one focal point. Multifocal IOLs represent an alternative means of achieving multifocality and are aimed at decreasing a patient's dependency on the traditional methods of vision correction following cataract surgery. The Array IOL (AMO, Irvine, Calif.) is the only multifocal IOL that has been granted FDA approval in the United States.

The Array

The Array is categorized as having a refractive lens design because of its ability to obtain multifocality due to a difference in optical refractive power in different areas of the IOL optic. The IOL is constructed with five different concentric rings, each of which possesses a unique refractive optical zone. As light passes through each zone, it is refracted to afford clarity at differing focal lengths. The Array is designed to have 50% of the light dedicated to the far image, 13% to the intermediate image, and 37% for near image clarity.¹

Study Data

Steinert and colleagues conducted a nonrandomized, prospective study that evaluated at a 1-year time interval the visual results of the Array lens compared to a traditional monofocal IOL.² The study included a subset of 102 patients who received an Array IOL in one eye and a traditional IOL in the fellow eye to diminish the effects of interobserver variability.

When examining the cohort of patients receiving both the multifocal and monofocal IOLs, the investigators determined that there was great similarity in each eye's ability to see well at distance. The average uncorrected VA was 20/32 in the eye implanted with the multifocal IOL and 20/30 in the monofocal eye. The best-corrected VA for the multifocal and monofocal eyes was 20/25 and 20/23, respectively. The differences between these two IOLs were evaluated in this study. Statistically, different outcomes in uncorrected near VA were achieved as the multifocal eyes achieved a mean uncorrected near VA of 20/33 as opposed to the monofocal group's uncorrected near VA of 20/54. This difference translates into an average difference of two lines on a reading card. There was no difference in best-corrected near VA between the groups. When both distance and near vision criteria were combined in this study, a higher percentage (77% vs. 46%) of eyes with the multifocal IOL achieved both a distance VA of 20/40 or better and a near VA of J3 or better than the eyes with the monofocal IOL.

Other investigators have achieved similar results. Arens and colleagues reported retrospectively on the results of a comparison of bilateral implantation of either multifocal IOLs or monofocal IOLs.³ It was determined that uncorrected and best-corrected distance VA did not differ between IOL groups. However, patients with multifocal IOLs experienced a significantly better near VA when corrected for distance vision.

Another criterion by which the multifocal IOL is assessed is its depth of focus. Multifocal IOLs are designed to simulate the crystalline lens's natural power of accommodation. In contrast to the monofocal IOLs that confer only a limited range of focus, multifocal IOLs offer patients a greater range of best-uncorrected VA at differing focal points. Steinert and colleagues evaluated depth of focus in their study and defined this term as the total range of focus between distance and near in which the VA was greater than 20/40.² Eyes with multifocal IOLs experienced a statistically significant increase in range of focus of nearly 1 D over eyes with monofocal IOLs. The benefit of increased depth of focus was most prominent for near focal points and resulted in approximately a three line increase in reading ability. These results were corroborated by other investigators who also sought to evaluate the depth of focus of the Array multifocal IOL. Both Arens and colleagues and Vaquero-Ruano and associates determined that depth of focus at near was significantly improved with the Array, while the multifocal and monofocal lenses functioned nearly identically at distance.^3,4

Disadvantages

The design of the multifocal IOLs predisposes these lenses to potentially diminished contrast sensitivity. As light is refracted through the numerous focal points on the lens, the retina is confronted with overlapping images from these points that can degrade image contrast and clarity. In their comprehensive study, Steinert and colleagues included contrast sensitivity testing of patients implanted with both a monofocal IOL and a multifocal IOL.² Although patients with multifocal IOLs experienced a statistically significant loss of best-corrected VA at low contrast levels, patients did not describe a loss of visual function nor did they perceive a disadvantage associated with this reduced level of function.

Arens and associates also compared contrast sensitivity in patients with monocular Array IOL implantation versus patients with binocular Array IOL implantation.³ The investigators found results similar to Steinert's; patients with monocular Array IOL implantation experienced decreased VA with diminishing levels of contrast. Interestingly, patients who underwent bilateral Array implantation did not experience any diminution of visual acuity at lower levels of contrast. The investigators postulated that this outcome can be explained by the phenomenon of binocular summation.³ They suggested that bilateral implantation of the Array lens should be performed to avert loss of low level contrast.

Patient Satisfaction

One year after implantation with the Array IOL, patients were evaluated for their visual performance and satisfaction levels.² Patients who underwent bilateral Array IOL implantation were asked to report on their level of visual function; 81% stated that they were able to function comfortably at near without spectacle correction. For intermediate and distance vision, the percentage of patients able to function well without correction was 93% for both multifocal and monofocal groups. Patients with bilateral Array implantation were also more likely to be spectacle-free than those with only unilateral Array implantation. Patients in this study were also questioned regarding their satisfaction with the visual outcomes of the surgery and if they would elect to receive a multifocal lens again. More than 90% of the patients in the study answered affirmative to each of the two questions. In the prospective study conducted by Vaquero-Ruano and colleagues, patients were also questioned about their experience with the Array IOL.⁴ All of the 50 patients in this study reported high levels of satisfaction with the Array lens and none of the patients opted for IOL explantation.

Conclusion

The Array multifocal IOL represents a significant advancement in the field of refractive cataract surgery. The Array offers patients uncorrected distance VA comparable to that of monofocal IOLs with the advantage of improved uncorrected intermediate and near VA. When implanted bilaterally, the lens seems to result in no degradation in visual function at any level of contrast sensitivity. Patient acceptance of this novel technology also appears to be high. Further refinements in multifocal optics will likely yield even greater options for patients seeking freedom from spectacles following cataract surgery.

References

1. Avitabile T, Marano F. Multifocal intra-ocular lenses. Curr Opin Ophthalmol. 2001;12(1):12-16.

2. Steinert RF, Aker BL, Trentacost DJ, et al. A prospective comparative study of the AMO Array zonal-progressive multifocal silicone intraocular lens and a monofocal intraocular lens. Ophthalmology. 1999;106:1243-1255.

3. Arens B, Fredudenthaler N, Quentin CD. Binocular function after bilateral implantation of monofocal and multifocal refractive intraocular lenses. J Cataract Refract Surg. 1999;25:399-404.

4. Vaquero-Ruano M, Encinas JL, Millan I, et al. AMO Array Multifocal versus monofocal intraocular lenses: Long term follow up. J Cataract Refract Surg. 1998;24:118-123.