IOL technology has evolved dramatically in recent years. Originally, the IOL was less dynamic, simply a replacement lens manufactured with one optical function—compensating aphakia. The function of modern IOLs has evolved, and current designs now also improve quality of vision, filter inadequate wavelengths of light that could disrupt the retina anatomically and functionally, and—perhaps most important—compensate for pseudophakic presbyopia at all distances including intermediate (70 cm) and near (40 cm). This is precisely the concept of premium IOLs.
VALUE-ADDED TECHNOLOGY
The word premium signifies value added; in the case of premium IOLs, the value added is the lens’ optical function, designed to improve the quality of life following cataract or refractive lens exchange surgery. Technological innovations in IOL design are continually advancing, and, for the immediate future, premium IOLs will be the most profitable for lens manufacturers. Today, companies are capitalizing on this market, as it is continually increasing due to the aging of the population.
Contemporary premium IOLs can be divided into three categories: presbyopia-correcting IOLs, toric IOLs, and aberration-correcting IOLs. The scope of this article focuses on multifocal, presbyopia-correcting IOLs.
The optics of modern multifocal IOLs are either rotationally symmetric or rotationally asymmetric. Some multifocal IOLs modify the index of refraction, from the peripheral to the central part of the lens, so that the lens’ optical power changes depending on pupil size. Other presbyopia-correcting IOLs work by introducing asphericity or removing chromatic aberration from the lens optics to improve near and intermediate vision.
For a multifocal IOL to work efficiently, astigmatism must be completely eliminated. In most cases, multifocal IOLs induce a loss of contrast sensitivity and are therefore contraindicated in eyes with aberrated corneas or in patients with limited contrast sensitivity such as those with maculopathy, retinal dystrophy, glaucoma, or advanced senility.
OPTICAL PRINCIPLES
In my opinion, the perfect multifocal IOL exhibits the following optical and design principles:
(1) Focus dominant for far vision;
(2) Adequate disparity between near and far foci;
(3) Aspheric design;
(4) Available toric model;
(5) Pupil-independent mechanism;
(6) Good optical performance on the optical bench and in vivo;
(7) Good capsular stability;
(8) Low rate of posterior capsular opacification (PCO);
(9) Implantable through a sub–2-mm incision; and
(10) Demonstration of good visual outcomes for far and adequate outcomes for intermediate and near vision that can be adapted to the lifestyle of the patient.
Principle No. 1: Far focus dominant. Humans are diurnal predators. Our brain’s dominant need is for distance vision. Dominance of far vision also decreases the effects of focus overlapping that is typical of multifocal optical designs and reduces glare and halos.
Principle No. 2: Adequate disparity between foci. Multifocal IOLs that overlap foci to produce acceptable vision at intermediate distances can produce halos and glare. Therefore, the overlapping of foci should be minimized to decrease the incidence of glare. When less than 3.00 D of near vision add exists, the incidence of halos will increase.
Principle No. 3: Aspheric design. Aspheric lenses improve overall optical performance. The lens should be free from aberrations, as we now know that 20% of patients do not have what is considered the standard value of asphericity (0.27 μm), especially if they have previously undergone corneal refractive surgery.
Principle No. 4: Toricity available. If an eye implanted with a multifocal IOL is left with more than 1.00 D of astigmatism, laser touch-up is required. Surgeons should remember that 4% of patients have more than 3.00 D of corneal astigmatism; 70% have more than 1.00 D.
Principle No. 5: Pupil independence. Pupil size after surgery is unpredictable, as are environmental conditions. Therefore, the implanted lens should not depend on pupil size to obtain adequate performance for far or near vision.
Principle No. 6: Good optical performance. Industry is responsible for making sure that any IOL that reaches the market provides good performance at the optical bench. Once an IOL is implanted, however, intraocular conditions affect its optical performance, and this can decrease by more than 50% from what has been demonstrated on the optical bench. Therefore, optical quality and aberrations should be measured 3 months after lens implantation so that surgeons can study the quality of IOL designs.
Principle No. 7: Capsular stability. Instability in the capsular bag, resulting in tilt and decentration, is a major cause of photic complaints and starbursts. Stability should be guaranteed by the design of the IOL and the quality of its biomaterial.
Principle No. 8: Low PCO rate. Light scattering and PCO significantly decrease multifocal IOL performance and frequently lead to the need for Nd:YAG capsulotomy. Again, lens design and biomaterials should aim to keep the posterior capsule transparent.
Principle No. 9: Implantable through a sub–2-mm incision. In 2003, I described the concept of microincisional cataract surgery (MICS).1,2 The practice of MICS does not change the preoperative astigmatic or aberrometric corneal profile. Premium IOLs should be compatible with MICS, as surgery through a sub–2-mm incision helps the surgeon to control astigmatism and aberrations, two components necessary for the optimal performance of these lenses.
Principle No. 10: Good far, adequate intermediate, and near visual outcomes. The provision of excellent far vision should be the main goal of premium IOL implantation. However, the lens should also provide adequate intermediate function, such as office and domestic tasks, and adequate near functional vision.
LENS CHOICES
The surgeon should determine the needs of his or her patients on a case-by-case basis. In my practice, we consider the following lenses to be the best multifocal IOLs, as they meet the criteria outlined above. These lenses have been or are currently the subject of clinical investigation. We have found that outcomes with these lenses are superior to outcomes with the previous generation of IOLs:
1. Diffractive IOLs: FineVision (PhysIOL), AT.LISA Toric and AT.LISA Trifocal (both by Carl Zeiss Meditec), AcrySof IQ ReStor +3.0 D IOL (Alcon Laboratories, Inc.), Tecnis 1-Piece (Abbott Medical Optics Inc.);
2. Refractive IOL: Rayner’s multifocal line of IOLs;
3. Rotationally asymmetric IOL: Lentis Mplus (3.00 and 1.50 D adds; Oculentis GmbH);
4. Toric multifocal IOLs: Lentis Mplus toric (3.00 D add), AT.LISA Toric, AcrySof IQ ReStor Toric +3.00 D; and
5. Achromatizing IOL: Akromalens (Hanita).
Jorge L. Alió, MD, PhD, is a Professor and the Chairman of Ophthalmology at the Miguel Hernandez University, Alicante, Spain, and the Medical Director of Vissum Corp., Spain. Professor Alió states that he is a paid consultant to Topcon, Oculentis, and Carl Zeiss Meditec and has a royalty agreement with Hanita. He may be reached at tel: +34 96 515 00 25; e-mail: jlalio@vissum.com.
- Alio JL,Rodriguez-Prats JL,Galal A.MICS:Micro-incision cataract surgery.Republic of Panama:Highlights of Ophthalmology;2004.
- Alio JL,Fine HI.Minimizing incisions and maximizing outcomes in cataract surgery.Berlin/Heidelberg,Germany: Springer-Verlag;2009.
