Figure 9-5 Example of a zonal refractive multifocal IOL. Left, schematic frontal view. Right, schematic lateral view of the rotationally asymmetric, multifocal sector lens, which is made from a combination of 2 spherical surfaces of differing radii.
(Illustration by Mark Miller from information courtesy of Oculentis GmbH.)
Complications
Patient dissatisfaction with the quality of vision after multifocal IOL implantation should be addressed carefully. These patients should undergo a comprehensive evaluation of the ocular surface to the macula. Possible causes of visual disturbance should be excluded, such as dry eye, irregular astigmatism, vitreous opacities, cystoid macular edema or epiretinal membrane. Postoperative capsular opacification is of greater concern with multifocal IOLs because minimal changes in the capsule can cause early deterioration in vision. To achieve optimal vision, Nd:YAG capsulotomy may be required earlier or more frequently in patients with multifocal IOLs than in patients with monofocal IOLs. However, if IOL exchange is being contemplated, Nd:YAG capsulotomy should be deferred. Other possible causes of vision disturbance (eg, dry eye, irregular astigmatism, cystoid macular edema, or epiretinal membrane) should be excluded before an IOL exchange is considered. Multifocal IOLs may result in glare and halos around lights at night, although newer multifocal IOLs incorporate technology that substantially reduces these optical phenomena. Symptoms may be reduced through the use of nighttime driving glasses or instillation of topical brimonidine drops to reduce mesopic pupil size. In addition, most of these symptoms will decrease over time through neuroadaptation. Nevertheless, careful selection of motivated, well-informed patients is mandatory.
Custom or Multifocal Ablations
The excimer laser may be used to create a multifocal cornea. The potential for improving near vision without significantly compromising distance vision was investigated after it was noted that, following excimer ablation, the uncorrected near vision of many patients improved more than expected (Fig 9- 6).
Figure 9-6 Multifocal ablation. Corneal topographic map showing a multifocal pattern after hyperopic laser in situ keratomileusis in a 62-year-old with preoperative hyperopia of +4.00 D. Postoperatively, the uncorrected visual acuity at distance is 20/25–2 and at near is Jaeger score J1. Manifest refraction of –0.25 +0.75 × 20 yields 20/20. Corneal topography demonstrates central hyperopic ablation (green) with relative steepening in the lower portion of the pupillary axis (orange), which provides the near add for reading vision. (Courtesy of Jayne S. Weiss, MD.)
A number of ablation patterns are being evaluated, including the following:
a small, central steep zone ablation, in which the central portion of the cornea is used for near and the midperiphery is used for distance vision
an inferior near-zone ablation
an inferiorly decentered hyperopic ablation
a central distance ablation with an intermediate/near midperipheral ablation
Some of these patterns generate simultaneous near and distance images, whereas others rely on pupillary constriction (accommodative convergence) to concentrate light rays through the steeper central ablation.
Although the excimer laser offers some potential advantages, results of multifocal corneal ablations have been disappointing to date.
Alarcón A, Anera RG, del Barco LJ, Jiménez JR. Designing multifocal corneal models to correct presbyopia by laser ablation. J Biomed Opt. 2012;17(1):018001.