The first foldable IOLs were manufactured from silicon. Silicone polymers are any of a large class of polysiloxanes, which are very stable over a wide range of temperatures. They possess an alternating silicon–oxygen atom backbone with organic side groups attached to the silicon atoms. The first silicone material used in the manufacture of IOLs was poly(dimethylsiloxane) [PDMS], which has a refractive index of 1.41. This was termed first-generation silicone. Poly(dimethyldiphenylsiloxane) [PDMDPS] is the later, second-generation silicone IOL material in use today. It has a higher refractive index of 1.46, so IOL optics manufactured from it can be thinner.

Silicones derive their flexibility from both their chain structure, alternating silicone–oxygen bonds that create large bond angles allowing rotation about the silicon–oxygen bonds, and their intermolecular structure in which tight chain packing is not possible. Substitutional modifications along the chain silicon atoms can be made to modify overall material properties, most notably flexibility and refractive index. These are the only nonhydrocarbon polymers in general use and were developed primarily because of their ease of fabrication and thermal stability. They incite little inflammatory reaction and are used in scleral buckling implant materials, heart valves, shunts, and other surgical devices.

Major manufacturers of silicone materials include AMO (SI40 series and Clariflex); STAAR Surgical (AA4203); and Bausch & Lomb (SoFlex series).

“Acrylic” is actually defined as any compound that can be considered to be derived from acrylic acid. In general terms, it is used to apply to any type of plastic made from acrylic monomers. For example, the PMMA of Ridley’s first implant was designated as an acrylic material.

With the introduction of the AcrySof IOL, the term acrylic was expanded to define a new type of foldable IOL optic material, one composed of acrylic monomers, and also to distinguish it from the other foldable material of the time, silicone. The two adjectives hydrophobic and hydrophilic are used to modify the term acrylic as it pertains to IOL chemistry. The modifying terms are used based on the, wet ability or more accurately, the contact angle measurement, of the material and the water content of the material.

As of 2009, the hydrophobic acrylic IOLs available to U.S. surgeons were the AcrySof (Alcon Surgical) and the Sensar AR40 and AR40E (AMO Surgical). What about the hydrophobic Tecnis? What about the Hoya IOL? They received the FDA approval in 2008—they are not selling in the US?

Introduced in 1995, the AcrySof IOL is manufactured from hydrophobic acrylic materials with cross-linked polymers or copolymers of acrylic esters and is less than 1% water. It is available as a three-piece in 5.5-, 6-, and 6.5-mm optics with bonded PMMA modified-C haptics in overall lengths of 12.5 and 13.0 mm (the MA series: 30, 60, and 50), and as a single-piece lens (the SA and SN series). All IOLs feature a nonreflective surface of the optic edge. This treatment is applied to the haptics in the single-piece design as well. There is a 5.50-D base curve on the posterior surface, with the remaining refractive power applied to the anterior surface.

Alcon has incorporated two additional features as combined options into its AcrySof platform: a light-normalizing blue blocker (SN) and the posterior aspheric surface (WF). The AcrySof single-piece toric IOLs were approved by the FDA in 2005. The AcrySof IQ Toric (aspheric and toric IOL) was approved by the FDA in March 2009. The FDA approved the diffractive-refractive pseudoaccommodative IOL (ReSTOR D3), and the D1 model with lower add and aspheric features became available. Both multifocal IOLs are available in three-piece and single-piece designs.

In the initial models, the high-index plastic and squared edge combined to cause an increased incidence of unwanted photic phenomenon, such as glare, rays, and temporal dark shadows (dysphotopsia) in a few patients. The glare and rays have almost been eliminated after Alcon engineers placed the power curve on the anterior optic surface and made the optic edge thinner and nonreflective (frosted square edge). The incidence of temporal shadows or temporal obscurations of vision do not seem to have been influenced as much by those design modifications. It was hypothesized that the corneal edema associated with a beveled temporal incision contributes to this transient negative dysphotopsia.⁷⁹

In 2000, the FDA approved the second foldable acrylic IOL, the Sensar AR40 (AMO Surgical) three-piece foldable IOL. This IOL featured a round edge optic. The edge was modified (AR40e) incorporating a PCO inhibiting posterior square edge and a compound rounded middle and anterior edge design to reduce the incidence of light reflections. On October 2007 AMO received the FDA approval for the Hydrophobic Tecnis IOL.

Another Hydrophobic IOL that received the FDA approval on September 2008 is the Hoya Spheric Model YA-60BB Intraocular Lens.

For the last three decades IOLs fabricated from hydrophilic materials have occupied a back seat to silicone and hydrophobic acrylic because of technical complexities, varying degrees of bioincompatibility, and several cases in which the whitish discoloration on the optic surface or within the optical component occurred and required explanation. It is now known that these problems occurred only in poorly fabricated designs. Well-manufactured IOLs, for example, the series of Rayner IOLs, properly manufactured with their Rayacryl material, have not had that problem. More than four million of these lenses have been implanted over the past 10 years without a report of primary calcification that had given this category of lenses a poor reputation.

The high-water-content acrylic hydrogels are the descendants of the 38% high-water-content IOGEL composed of HEMA, which was not approved by the U.S. FDA (circa 1992) because of its tendency for intravitreal dislocation after YAG laser capsulotomy. It should be emphasized that the demise of this IOL and some others in this era was not because of lack of biocompatibility, but rather design problems that precluded good fixation of the IOL.

Hydrophilic acrylic IOLs are packed in fluid (wet packed). They are packed in a vial containing distilled water or balanced salt solutions; thus they are already in the hydrated state in their final dimensions within the container. These lenses are flexible, enabling the surgeon to fold and insert/inject the lens through small incisions.

The Bausch & Lomb Hydroview entered the international market in 1995. It was the first hydrophilic acrylic IOL to be approved by the U.S. FDA. However, in May 1999, the manufacturer first received reports about clouding of a small number of Hydroview IOLs. Analysis performed at Dr. Apple’s laboratory revealed that the optical surfaces of the IOLs were covered almost completely by a layer of granular deposits on both anterior and posterior surfaces. The granules noticed on the optical surfaces stained positive with several calcium stains (1% Alizarin red, von-Kossa) (Fig. 11-56). Surface chemistry studies performed by Bausch & Lomb identified the lens deposits as a layered mixture of calcium phosphate, fatty acids, salts, and small amounts of silicone. This model, according to the manufacturer, revealed a migration of silicone from the gasket in the lens packaging onto the surface of the IOL. The models also indicated a possibility that in addition to silicone, fatty acids needed to be present to attract calcium ions to the lens surface. A compromised blood-retinal barrier also seemed to be associated with the appearance of calcified deposits. Therefore, fatty acids and silicone, perhaps in association with a metabolic disease in the affected patient, could result in the calcification.

In May 2001, on the basis of this evidence, the manufacturer changed the packaging of the Hydroview. The new packaging retained the ease of use of the previous SureFold components, but it was sealed with a gasket made from a perfluoroelastomer. The company states that calcification has not been reported in any of these IOLs. (I am not sure that it is still available; in the website of B&L, I could not find the IOL.) There were more opacification cases in England after the company had changed the gasket⁸⁰

The MemoryLens by Carl Zeiss Meditec (formerly Ioltech, formerly by Ciba Vision, Duluth, GA) was introduced in 1989. The thermoplastic properties of the IOL are unique. The polymer used for the manufacture of the optic of this lens contains 59% HEMA, 16% methyl methacrylate, 4% 4-methacryloxy 2-hydroxy benzophenone UV absorber, and 1% ethylene glycol dimethacrylate. The haptics are made of polypropylene (Prolene). The lens is prefolded and remains glassy and stiff at room temperature. The prefolded MemoryLens can be implanted directly from the container without any requirement of folding instruments. The container with the lens is kept at a temperature of 8°C. After intraocular insertion, and under the influence of body temperature, the lens unfolds slowly (∼15 minutes) providing an atraumatic and controlled implantation.

Reports on granular deposits on the optical surface component of the MemoryLens led Ciba Vision to voluntarily withdraw the lens from the market in April 2000. Analyses performed in Dr. Apple’s laboratory on some of those lenses demonstrated that the deposits were in part composed of calcium/phosphate. Analyses performed by the manufacturer revealed that a biofilm, composed of different proteins, in addition to calcium/phosphate, was covering the optic surfaces of the affected lenses. The company modified their tumbling process used in lens polishing, thus changing the surface characteristics of the lens in the hope of avoiding the unwanted biofilm. No new cases of this problem have been reported with this new lens design. After identifying and correcting the problem, the manufacturer received approval from both the U.S. FDA and the European regulatory authorities to return the lens to the market. Ciba Vision re-released the MemoryLens as model CV232. This maintains the same basic characteristics of the previous models, but in addition has an incorporated square posterior optic edge for PCO prevention. The CV232 model allows surgeons to place this IOL through a 3.2-mm incision. In 2005, few cases of cleft, cavitation, or schisis of the IOL were identified by Dr Apple’s laboratory, the speculated mechanism leading to include a variation in the polymer and/or tighter rolling of the IOL after its relaunch than in the earlier version, in which no such occurrence was observed. During the folding process, the pressure applied to the IOL causes the anterior portion of the IOL to expand laterally while the posterior portion of the IOL compresses centrally. This may result in opposing forces inside the IOL, especially at the central portion, which can lead to movement of the anterior and posterior portions of the IOL in opposite directions. Changes in the manufacturing process of the IOL may result in an IOL material that is not cohesive enough to withstand these conflicting forces. This may result in an internal crack or cleft in the IOL, such as observed in Dr Apple’s laboratory. In a later stage, after implantation, this cavity may fill with aqueous humor.^81,82

The STAAR Surgical Collamer IOL (CC4204BF) is a plate haptic, single-piece foldable lens manufactured from a collamer material. The overall length of the IOL is 10.8 mm (11.2 mm corner to diagonal corner) with an optic diameter of 6.0 mm. The haptic design has two 0.9-mm fenestrations to facilitate capsular fixation. These fenestrations are smaller than those of 1.15 mm incorporated into STAAR’s silicone plate haptic IOL.

This acrylic IOL is composed of a hydrophilic collagen polymer (copolymer of 63% hydroxyl-ethyl-methyl-acrylate, 0.3% porcine collagen, and 3.4% of a benzophenone for UV absorption), with a water content of 34%, a light transmission of 99%, and a refractive index of 1.45 at 35°C. It is also available as a three-piece model with a square posterior optic edge (CQ2015A).

The Rayner C-flex, formerly Centerflex (Rayner Intraocular Lenses Ltd.), is a single-piece, hydrophilic acrylic IOL, which began FDA trials in the United States in 2004 and gained U.S. FDA approval in may 2007. Studies in Dr. Apple’s laboratory have confirmed that this IOL and its basic polymer material have not been associated with the opacification/calcification and decentration problems seen with the previously mentioned IOLs, as well as the others that unfortunately have, until now, given this category of material a bad name. The C-flex lens has extended closed loops or haptics that render a general configuration of standard one-piece modified C-loop IOL designs. This type of platform helps provide stability of the lens optic in all three axes, an advantage that should be useful as new refractive or other specialized elements are added to this basic lens. The optic size of this lens is 5.75 mm with an overall diameter of 12.00 mm. The lens is made of a copolymer of hydrophilic and hydrophobic methacrylates with a water content of 26%, namely, HEMA and methyl methacrylate. Its material incorporates a benzophenone UV-absorbing agent, and it is inserted into the eye by means of a disposable cartridge-injector system (Fig. 11-57).

The original Centerflex model had a square edge around most of the optic edge, but the optic edge remained continuous with the haptics, and therefore, it was rounded and continuous where the haptics attached to the optic (Fig. 11-58). Dr. Michael Ammon (Vienna, Austria), in observations of clinical cases, and Dr. David J. Apple, in observations of pathologic specimens, postulated that the optic-haptic junction might represent a structural vulnerability for epithelial cell invasion, or as termed by Dr. Apple, an Achilles heel, in which the lack of the 360-degree square optic edge may inhibit the IOLs ability to block ingrowth of lens epithelial cells (LECs) over the visual axis.⁸³ Both of these authors have furthermore postulated that the continuation of the square edge in the region of the optic-haptic junction would provide a complete 360-degree physical barricade against invading epithelial cells that cause PCO.

In rabbit studies completed at Dr. Apple’s laboratory, it was noted that the subsequently improved model 570C featuring a discontinuous enhanced edge provided the best barrier effect against cell migration/proliferation and PCO formation.⁶⁵ Analyses of the scanning electron photomicrographs demonstrate this model’s complete ridge or enhanced edge extending for 360 degrees around the lens optic (Fig. 11-59). It is this enhanced-edge model 570C that underwent FDA trial. Another advantage of the C-flex IOL is its ability to serve as a drug delivery system for the fourth-generation fluoroquinolones after presoaking the IOL in the antibiotic solution.^84,85

Another hydrophilic IOL, the Bausch & Lomb Akreos Adapt is a one-piece lens, with four fixation points, made of the unique Akreos hydrophilic acrylic material. The biocompatible lens material has a long-term safety record, with more than 2 million implants since 1998. Akreos Adapt is implanted with its single use Hydroport injector (PS27) for a 3.2-mm standard injection.

Faulty hydrophilic designs have been largely weeded from the market, and more recent experiences such as noted with the Rayner design have altered negative attitudes about this category.

Concerns about human eye retinal damage by UV radiation emerged because of the results of animal light toxicity studies in the late 1970s.^87,88,89 This awareness stimulated the IOL industry to develop ultraviolet radiation (UVR)-filtering (215–400 nm) IOLs, especially because there should be no downside, that is, UVR did not contribute to vision. But, when these IOLs were introduced in the early 1980s, questions were raised regarding toxicity of the UVR-filtering chromophore⁹⁰ and its potential for long-term leaching and possible release during Nd:YAG laser posterior capsulotomy. Unproven stability, safety, and lack of clinically demonstrated benefit of safety for these IOLs added to initial skepticism. The U.S. FDA testing for of the UVR-filtering material addressed these concerns, as did demonstration of protection by such filtering in animal experiments.⁹¹ Human studies^92,93 demonstrated a need for protection from UVR. As a result, by the mid-1980s, virtually all manufacturers decided to offer only IOLs with an incorporated UVR-filtering chromophore. The Crystalens is a notable exception in offering very little UV protection.

In 1978, Mainster⁸⁸ discussed retinal damage from intense near-UVR light sources after providing measurements of a non–UVR-filtering PMMA IOL and comparing it with that of human crystalline lens data from the literature.⁹⁴ He recognized the need for tinting IOL material. But because of the excellent visual results of nonblue light-filtering IOLs at that time, and to avoid new materials, he suggested continued formulation of permissible exposure levels of UV radiation and continued counseling pseudophakic patients about possible occupational or environmental hazards to excessive visible light. Zigman⁸⁹ supported yellow tinting of IOLs, citing his own earlier experiments in animals, which showed retinal damage even with nonintense near-UVR sources. He cited references^95,96 on the yellow color of the crystalline lens of several species including human. He gave other circumstances such as light sensitivity, exposure to light-sensitizing drugs, and excessive glare, for which he suggested tinting of IOLs. He even created light-normalizing PMMA by a degradation process with UV radiation on an existing IOL material and IOLs made from it.⁹⁷ In 1983, Sliney⁹⁸ reported that removing wavelengths of light less than 500 nm would filter out only 10% of useful visible light but would remove 97% of harmful UV and blue radiation. In 1985, Marshall reviewed the issues of radiation and the aging eye⁹⁹ and suggested tinted IOLs so that they would transmit light in similar fashion as the natural human lens. Filtering of UVR and blue light for pseudophakic eyes was also suggested in 1986.^100,101 Similarly in 1987 Mainster¹⁰² reviewed the possible link between light and macular degeneration and recommended UVR and deep blue protective sunglasses for aphakic and pseudophakic eyes without any blue light-filtering IOL as precaution until the relationship between photic retinopathy and age-related macular degeneration (AMD) might be better understood. In addition to these studies, animal electroretinography (ERG) research,^103,104 laboratory lipofuscin fluorophore A2E assessments,¹⁰⁵ and human vitreous autofluorescence and fluorophotometry¹⁰⁶ all suggest a potential benefit by reducing the amount of blue light overexposure experienced in UV-filtering IOLs.

In 1987, Young¹⁰⁷ wrote a review on pathophysiology of AMD and followed up next year with a review¹⁰⁸ on the hypothesis that solar radiation plays a key role in AMD and suggested both antioxidants and protective radiation filters be intrinsic components of a program of preventive medicine. As of 1988, it was recognized that although the need for sunglasses in very bright sunlight could not be met by an IOL, at least filtering as much as possible damaging UV and blue light for all light conditions in pseudophakic eyes might be reasonable.

Anil Patel, Ph.D., was the chief scientist at CooperVision in the early 1980s and contributed significantly to the development of UVR blocking and blue light–attenuating IOLs. At CooperVision he also worked on phototoxicity safety issues for its argon laser delivery system for retinal photocoagulation. In a historically interesting parallel, he had become part of the CooperVision organization through its acquisition in 1979 of the dental company Cavitron (New York). Before the acquisition, he made presentations to the FDA about phototoxicity considerations of a new UVR light source (Quicklite), which was used in the curing of dental material.¹⁰⁹ Of course, CooperVision acquired Cavitron because it was Cavitron that manufactured the ultrasonic teeth-cleaning machine on which Dr. Charles Kelman based his first phacoemulsifier.¹¹⁰

Before the introduction of the foldable AcrySof Natural IOL, Hoya Corporation of Japan had created a similar yellow IOL in PMMA with chemically unbound yellow chromophores, in the early 1990s with a Japanese patent application date of early 1988.¹¹¹ It had yellow dye but was not foldable; thus it was not significantly used inside or outside of Japan. It is interesting to note that Hoya created it primarily to reduce the frequency of clinical cyanopsia noted in pseudophakic patients. There exist several publications^{112,113,114,115} reporting that patients with pseudophakic vision with clear IOLs have color distortion because of excessive blue light, a characteristic called cyanopsia or dyschromatopsia. It is interesting to mention that the French artist Claude Monet chose yellow cataract spectacles (on one side) as he continued painting in old age after his cataract removal circa 1920 (Fig. 11-60). There are several publications on clinical studies of the Hoya PMMA IOL, which showed safety and normal color vision,¹¹⁶ improved contrast sensitivity,¹¹⁷ and long-term efficacy in decreasing blood-retinal barrier disruption.¹⁰⁶ A subsequent publication found no clinically significant change in color contrast sensitivity between the AF-1 (UV) (Hoya) in one eye and the AF-1 (UY) (Hoya) in the other.¹¹⁸ An additional study compared two other IOLs by the same manufacturer (Hoya yellow-tinted YA60BB vs non-tinted VA60BB) and found no significant differences in photopic or mesopic contrast acuities. No difference in color perception was reported 3 months after surgery.¹¹⁹

Menicon Corporation introduced a yellow-tinted IOL in Japan in 1994. It too was nonfoldable and thus not used in any significant numbers inside or outside Japan. Hoya Healthcare Corporation introduced a foldable Hoya Acryfold-1 (UY) IOL¹²⁰ which is a UVR- and blue light-filtering IOL composed of Hoya’s hydrophobic acrylic material. At the 2004 ASCRS meeting¹²¹ a color vision expert from Japan presented a foldable light-normalizing silicone IOL from Canon.

Light-normalizing IOLs were also used in Sweden, and although ultimately no product came from Pharmacia, it patented¹²² a yellow PMMA material. ERG studies in rabbits^103,104 in Sweden in the late 1980s showed that yellow filters protected the rabbit retina from light damage. Light-normalizing IOLs have been used in Russia as well. Since the mid-1980s, approximately 500,000 yellow-tinted PMMA IOLs have been implanted in patients at the S.N. Fyodorov Eye Microsurgery State Institute in Moscow, Russia (Fig. 11-61) (personal communication, Boris E. Malyugin, M.D., Ph.D., September 2004).

In the fall of 2003, Alcon Surgical introduced the AcrySof Natural IOL, the first foldable light-normalizing IOL. The AcrySof Natural IOL with Alcon’s proprietary violet and blue light-filtering chromophore filters light in a manner that approximates the human crystalline lens in the 400- to 475-nm blue light wavelength. In addition to standard UV-light filtering, the AcrySof Natural IOL reduces transmission of blue light wavelengths by 71% at 400 nm and by 22% at 475 nm. The details of the creation of the bondable nonleaching, nontoxic, inert biocompatible patented dye for the foldable light-normalizing AcrySof Natural IOL material are proprietary to Alcon with several patents for the dye and material.¹²³ The transmission characteristic for the light-normalizing single-piece AcrySof Natural IOL is on average similar to that of a 25-year-old natural crystalline lens, and provides comparative transmission spectra for the current AcrySof Natural IOL, the UVR-filtering single-piece AcrySof IOL, and the range of a 4- to 53-year-old human crystalline lens (Fig. 11-62).

This lens is manufactured by using the platform of the single-piece AcrySof and has been shown to be safe and effective in terms of biocompatibility and visual performance^124,125,126 but the protective effect of this lens is still controversial and needs to be further investigated.

Questions about the accuracy of color vision perception and the quality of vision in photopic, mesopic, or scotopic circumstances seem to have been raised for three reasons.

First, while there are multiple blue light-filtering IOLs available outside of the United States, each with their own transmission characteristics,¹²⁷ the proprietary nature of the chromophore bonding chemistry gave a marketing exclusivity to the Alcon Company, which is the only manufacturer able to provide a foldable light-normalizing IOL in the United States.

Second, although there are some studies that suggest that there may be an increase in the progression of macular degeneration after cataract surgery,^{128,129,130,131} there are no studies demonstrating a reduction in the incidence of new macular degeneration or its progression in patients receiving the AcrySof Natural IOL versus those receiving conventional UVR-filtering clear IOLs. Existing population studies are difficult to interpret because of vastly different study methods of phakic eyes; a lack of uniformity in what defines macular degeneration; inherent differences in genetics, diet, and general health standards; and environmental experiences of the subjects. Because of these problems many of the current large epidemiologic studies are in fact contradictory. Epidemiologic studies are difficult to interpret because some studies have shown a correlation between macular degeneration and light exposure, whereas others have not.^{132,133,134,135,136,137,138,139,140} Studies of the retina and macular degeneration after cataract surgeries have also produced conflicting results.^{128,129,130,141,142,143,144,145,146} Several reports,^{129,130,131,147,148} a postmortem study,¹²⁸ and data from the Beaver Dam Eye Study¹⁴⁹ have raised concerns that cataract surgery could increase the development of late age-related maculopathy (ARM) (neovascular ARM or central geographic atrophy) or progression to late ARM in eyes with early late-stage ARM lesions (soft drusen and retinal pigmentary abnormalities). Other studies have demonstrated a nonrelationship between cataract surgery and AMD.^145,150,151

Third, there has been a value theorized for the relatively excessive short-wavelength blue light transmitted by non–light-normalizing IOLs for actually improving vision in scotopic conditions.¹⁵² There is a concern that patients might not function as well in scotopic conditions if this short-wavelength blue light is removed.^88,152,153 Older adults have difficulty seeing in dim environments especially if they have early AMD,^{154,155,156,157} but the practical utility of scotopic vision is interesting to consider. It is colorless, pure rod night vision ranging in luminance from 0.000,001 cd/m² to 0.001 cd/m² (a moonless overcast night). Scotopic sensitivity is available when light energy is insufficient to stimulate cone photoreceptors. At these levels of illumination, which would be exemplified by a moonless overcast night, only rod receptors are active.

However, mesopic vision is much more valuable and practical for humans as it is experienced within intermediate luminance levels.¹⁵⁸ It starts as a moonlit night extending to the levels of light experienced at early twilight or dusk. It is a common misconception that cones function only in the day and rods only at night. Both rods and cones function simultaneously within mesopic limits and when color is just beginning to become visible. From a practical standpoint, the levels of illumination encountered during night driving represent mesopic conditions.¹⁵⁹

As to vision in mesopic and photopic ranges of luminance, a well-controlled comparative study with control of pupillary aperture has been reported.¹¹⁷ This study demonstrated improvement in contrast sensitivity for the midspatial frequencies of 6°C and 12°C and a reduced effect of central glare on the contrast sensitivity for light-normalizing IOLs.

Considering non–light-normalizing IOLs, there may be a tradeoff for any relative potential increase in scotopic sensitivity. Photochemical damage potential increases as wavelength shortens from green to higher-energy blue light. The potential of a few more photons to pass through a UVR-filtering IOL for scotopic night vision as a benefit in the aging pseudophakic eye needs to be balanced with the consideration of allowing the potential of exposure to 1,000,000,000 times more blue-light photons during bright daylight vision.¹⁶⁰

There have been measurements made in several categories of scientific study that support the use of spectrum-normalizing IOLs. In addition to studies already mentioned, animal ERG research,^103,104 laboratory lipofuscin fluorophore A2E assessments,^105,161 and human vitreous autofluorescence and fluorophotometry¹⁰⁶ all suggest a potential benefit by reducing the amount of blue-light overexposure experienced in UV-filtering IOLs. Human retinal pigment epithelium (RPE) cells have been exposed to blue light and were found to have a more significant reduction in apoptosis when an AcrySof blue-light filter was used than when an AcrySof UV filter was used.^161,162 Vascular endothelial growth factor (VEGF) production has been used as an indictor of cell damage in A2E-laden RPE cells exposed to white light. Cells exposed to the light through a blue light-filtering lens material had significantly less VEGF up-regulation than those exposed to light through a UV-blocking lens material.¹⁶³

Currently, scientific literature does not directly or indirectly prove the effectiveness of light-normalizing IOLs in preventing AMD or maintaining functional scotopic vision.¹⁶⁴ A provisional argument has been made to acknowledge the general principle that the body’s repair processes become increasingly less efficient as exposure to environmental stimuli accumulates and that protection against those stimuli may be beneficial. But in the eye, it is difficult to discriminate between problems produced by a lifetime of light stimulation and those that may be seen as a result of a normal reduction in the effectiveness of repair mechanisms over time. They may be actually inseparable viewpoints of the senescent effects of the passage of time moderated by variations in the predispositions of genetics, nutrition, and lifetime radiation exposure.

Even internationally known experts do not agree as to the value of light-normalizing IOLs. Mainster and Sparrow¹⁵² reached different but somewhat similar conclusions about light protection in the bright outdoor sunshine. Mainster preferred a UV-filtering IOL plus sunglasses for use outdoors, whereas Sparrow preferred a UV- and blue light-filtering IOL and sunglasses.

At this point it is unknown whether blue light-normalizing IOLs will have any effect on the incidence or progression of AMD. In trying to consider this question, scientists and surgeons have begun to consider not only the concept of cumulative exposures but also the cumulative risks and benefits. The benefits of light-normalizing IOLs might be (a) elimination of cyanopsia, (b) improvement of contrast sensitivity and reduced glare effect¹²⁶ in mesopic and photopic conditions, and (c) a potential protective effect of foveal function. The risk might be the loss of photons, which may have the potential for creating improved scotopic vision and interference with circadian rhythm.

The circadian system coordinates the timing of multiple biologic events to a specific phase of the 24-hour environmental cycle. Entrainment is the proper synchronization of a biologic entity to the daily light-dark cycle. This photoentrainment has been thought to occur because of visible light perceived by rods and cones. In 2002, it was discovered that the primary contribution for entrainment may actually come from intrinsically photoreceptive retinal ganglion cells (ipRGCs) with rods and cones playing a secondary role.^165,166 These cells contain a photopigment called melanopsin that has maximum sensitivity to light in the blue part of the spectrum (around 480 nm). Since blue light-filtering IOLs reduce transmission in this range, arguments can be made regarding the potential interference with the amount of light available for proper entrainment. Seven different “action spectra” ranging from 480 to 492 nm have been discovered and labeled by their identifying research effort (usually their main author) since identification of the original peaked sensitivity of 480 nm in 2002.¹⁶⁷ Two action spectra were identified (both peaked at 460 nm) prior to the ipRGC discovery. Because of the longer wavelengths, the newer action spectra support a significantly higher comparative effectiveness for entrainment for blue light-filtering IOLs than the earlier action spectra of shorter wavelength. The results of photoentrainment computations expect the blue light-filtering IOL in 65- to 80- year-olds to be within +6% to -13% effectiveness of the normal adult lens of 30- to 40-year-olds. Although these many discussions are extraordinarily interesting, the contribution to blue light blocking literally pales in comparison to the vast environmental variation of individual living circumstances.¹⁶⁷

The validity of the potential long-term benefit of light-normalizing IOLs as a preventive measure for the preservation of macular vision needs long-term comparative clinical trials in pseudophakic eyes to be carried out similar to the AREDS study¹⁶⁸ for establishing the role of UVR- and blue light-filtering IOLs as a potential preventive measure against known loss of vision with further aging for all eyes and AMD for susceptible eyes. It may be discovered that the current blue light-normalizing IOLs may not have a preventive effect on the occurrence or progression of AMD. If no preventive effect is found, it is possible that an increased concentration of dye could be used to possibly render an effect. If an effect is found, it might be possible that a lesser concentration of dye might still be salutary. Long-term trials should yield answers as to the potential benefits of light-normalizing IOLs.

This study of the AcrySof Natural SN30AL was carried out, presented, and accepted by the U.S. FDA as part of the process to gain premarket approval.¹⁶⁹ Study results showed no significant differences in performance between SN30AL and SA30AL models with regard to visual acuity, contrast sensitivity, or color perception as measured by the Farnsworth-Munsell D-15 test. The material has passed all requisite biologic testing for degradation, leaching, mutagenesis, and carcinogenesis. This IOL was approved for commercial use in the United States by the FDA in 2003. Since then, more millions of cases have been performed with only one report of IOL exchange because of color vision misperception with the Natural IOL.¹⁷⁰ Contrast sensitivity and color discrimination with the Farnsworth-Munsell 100-Hue test have been confirmed comparing AcrySof Natural versus nontinted AcrySof SA60AT.¹²⁴ It has also been corroborated that the AcrySof Natural does not increase anterior chamber inflammation.¹⁷¹

As an aside, in J.A.D.’s clinical experience, color misperception after cataract surgery has been rarely observed in people in whom we thought might have the potential for ultrafine color perception (i.e., artists and engineers). Sometimes after surgery with conventional UVR-filtering IOLs, a rare number of those patients had difficulty with color-matching components of their wardrobes or work materials. They would report that things had a greater blue tint than they had before surgery. Likewise, in 200 cases of implanting a conventional IOL in one eye and an AcrySof Natural in the other (a unique situation that occurred during the introduction period of the Natural in which patients’ first eyes were implanted with a conventional IOL and their second with the pigmented version), J.A.D. has seen only two patients who noticed that colors seemed “whitish blue” with the conventional IOL versus “skin toned” with the AcrySof Natural IOL. Neither perception was favored, nor was the combination bothersome to those patients.¹⁶⁹

Because light-normalizing lenses are offered by only one company (Alcon) in the United States, some controversy still exists toward their acceptance and use.^172,173,174

It is critically important for the surgeon to develop an efficient routine to effectively evaluate patients’ candidacy for astigmatic correction—to develop the plan and then execute the plan. A disciplined routine of obtaining, evaluating, analyzing, and calculating preoperative and postoperative measurements needs to be established and followed. Hard or soft toric contact lenses should be removed for at least 3 weeks and soft at least 1 week before evaluations can occur. Testing should include manual and automated refraction, lensometry of current glasses, IOL Master (Carl Zeiss Meditec, Inc., Dublin, CA) axial lengths and keratometry length measurement, manual and automated keratometry, and computerized videokeratography. All test results should be in basic agreement or re-analysis and re-testing will need to be accomplished. Special care should be used in evaluation of the corneal surface and corneal videokeratography (CVK) images. Patients with corneal anterior basement membrane (ABM) dystrophy may exhibit some improvement in vision with various amounts of cylinder, but these refractions can change depending on the state of the ABM dystrophy (Fig. 11-64).

It must be remembered that all measurements, even the very reliable and repeatable ones obtained from sophisticated machines like the IOLMaster,¹⁸⁶ are subject to the device’s inherent limits of absolute accuracy; the numbers used for calculations should be thought of as the mean numbers that could be obtained from the device. Then it must also be remembered that the devices are being operated by humans, usually in a private practice setting, who have varying levels of training and abilities. This human factor also introduces a compounding range of accuracy for each number obtained from each device. There then must be a consideration for the cumulative error that can occur in an individual patient because of the results of theoretically derived formulae, calculations, rounding of the IOL power selection up or down to the nearest 0.5-D availability, axis marking, actual individual surgery incision location and effects, IOL placement accuracy, and actual IOL (A-P) final placement versus anticipated effective lens position, and rotational stability, all subject to a similar range of means and standard deviations. For each individual case, if the numbers are average, then we should get results that are average, which would be good clinical results. If some numbers come from one side of an extreme and others from the other side, then the results can still be average and good clinically. But if a preponderance of data and calculation errors come from one side of the extreme, the cumulative effect of the errors can combine to provide an extreme result from that side, viz, a result that is not average and does not seem to be clinically correct for spherical equivalent or cylinder. Small variations in individual ingredient performances can produce relatively large final result variations. The effects of cyclotorsion are somewhat variable,¹⁸⁷ but perhaps most important, theoretical estimations have shown that approximately 1 degree of off-axis rotation can result in a loss of up to 3.3% of the IOL’s cylinder power, so a 10-degree variation from perfect can result in a 33% loss of effect.¹⁸⁸ After all of these considerations, it seems like somewhat of an intellectual contradiction to depend on a marking pen dot at the 6 o’clock limbus that may be 5 degrees wide even if perfectly applied.

A clinical case example is the left eye of a 70-year-old male operated by J.A.D. who had a preoperative manifest refraction of -3.00 × 086 degrees, keratometry 43.27 × 43.89 at 116. We had populated the Alcon Toric IOL calculator with an incision location of 10 degrees and a surgically induced astigmatism incision factor of 0.32 D. With that input, the calculator predicted that a T3 toric IOL placed at 111 degrees would leave a refractive cylinder residual of 0.12 D at 021 degrees. However, the patient’s final refraction was + 0.75 to 1.25 × 085 for 20/20. He expected to see well without glasses but did not, and he was unhappy with his investment in the toric IOL option, which should have delivered better uncorrected distance vision. He was presented with options, and he selected a refund of his upgrade fee and was happy just to wear the glasses that he had already purchased.

This second example demonstrates the difficulty in the possible effective use of an IOL, which might correct 0.50 to 0.75 D of astigmatism. There would be a lot of prospective patients, since J.A.D.’s current use distribution of AcrySof toric IOLs is 50% T3, 25% T4, and 25% T5. But, the currently available measurement and formula validities and accuracies might not provide enough reliability to deliver good results to each individual patient with that small amount of preoperative keratometric astigmatism.

There are various methods to align the toric IOLs. Some are complex photographic iris anatomy registration techniques^180,189 and some involve limbal marking at the slitlamp. Carefully applied slitlamp markings have been found to have similar accuracy to photographic iris registration.¹⁹⁰ One more basic routine involves making a small mark with a pen at the 6 o’clock corneal limbus (3 and 9 o’clock marks are also popular) with the patient seated (but not using a slitlamp) so as to avoid the occasional cyclotorsion effects of recumbency, and marking the desired orientation of the toric IOL (Figs. 11-65–11-70). Another way to have a long-lasting mark is by creating a small scratch of the corneal epithelium on the periphery of the cornea. During IOL insertion, the IOL is rotated to a position about 20 degrees short of its final desired axis position. It is important to remove all viscoelastic in front of and behind the IOL before final positioning because even a small amount of residual viscoelastic may create postoperative rotation in larger eyes and even the process of removal of viscoelastic can change final IOL orientation.¹⁹¹ It is important to have seated the IOL haptics and optic so that they are in a neutral position. The aim of the surgeon is to align the mark on the IOL with the desired axis mark on the cornea that was prepared by the surgeon at the beginning of the surgery (based on the orientation mark that was made while the patient was sitting). The AcrySof toric IOL may even be used without problem in cases where an anterior radial capsular tear has occurred during surgery. The 0.4-mm square haptics are long enough so that they can bridge an anterior radial tear, which extends to the capsular bag equator and will also provide enough friction so that the IOL will not rotate after placement (Fig. 11-71). Although correct placement is relatively easy, there are multiple assumptions that need to be made prior to surgery to end up with a good optical result.

In the United States, only two models, the STAAR and AcrySof IOLs, are available. The other models mentioned in the following paragraphs are available in Europe and elsewhere.

The first aspheric IOL to appear commercially was the Tecnis Z9000, a foldable, 3-piece silicone IOL. The Tecnis Z9000 is a CeeOn Edge IOL model 911 with a modified prolate anterior surface. This alteration lowers the refractive power of the IOL at its periphery, inducing a negative SA. This negates the effects of overrefraction at the periphery of the optical zone at the cornea responsible for corneal-induced spherical aberration. The Tecnis Z9000 and the related Tecnis Z9002 and Tecnis ZA9003 were designed to fully negate the average corneal SA by inducing a negative SA at 6 mm of -0.27 μm.

Another aspheric IOL, the AcrySof IQ, was developed by Alcon. It has the same ultraviolet and blue light-filtering chromophores as those found in the single-piece acrylic AcrySof Natural IOL (SN60AT, Alcon). The unique feature of the AcrySof IOL is the posterior aspheric surface that adds -0.20 μm of spherical aberration to the eye at the 6.0-mm optical zone. This only partially corrects corneal SA, leaving the average patient with residual positive SA. A small amount of residual SA could benefit the patient by increasing depth of field, allowing the patient to better tolerate some residual ametropia and be less dependent on spectacle correction for near tasks.

For aspheric IOLs that induce negative SA, such as the Tecnis or AcrySof IQ, to be maximally beneficial they need to be well centered and without tilt.²⁰⁰ If the aspheric IOL is not well centered, the induced HOAs from the malpositioned aspheric can cause the IOL to perform worse than a spherical IOL decentered to the same degree.^199,200 Decentered spherical IOLS are expected to increase ocular coma and other aberrations as well²⁰¹ but not to the same degree.

In light of this problem, Bausch & Lomb introduced the SofPort Advanced Optics model LI61 AO (Fig. 11-77). The SofPort IOL is an equiconvex silicone lens with prolate anterior and posterior surfaces. The aim of the IOL is to be perfectly aspheric and not induce HOA with tilt or decentration. Unlike the AcrySof IQ or Tecnis IOLs, which are designed to outperform spherical IOLs only up to a specific limit of tilt and/or decentration,²⁰¹ the SofPort IOL should outperform a spherical IOL at a much larger range of optic orientations.²⁰² However, because the SofPort does not reduce corneally induced SA, a well-centered Tecnis or AcrySof IQ IOL with minimal decentration or tilt should theoretically outperform the SofPort IOL in the average patient.

In recent years, other aspheric IOLs appeared in the market. These new models tend to imitate the basic strategy of one of the three IOLs mentioned previously; they either fully correct the average corneal SA like the Tecnis, partially correct the average corneal SA like the AcrySof IQ, or aim to be perfectly aspheric like the SofPort IOL. The Softec HD by Lenstec, (Clearwater, Florida) features a proprietary aspheric treatment to both anterior and posterior optic surfaces of its single-piece hydrophilic plastic. It has been presented that the biaspheric IOL is less sensitive to decentration and tilt. Perhaps most important, the company makes its IOLs available in quarter-diopter intervals rather than the industry standard half-diopter interval.

Holladay et al¹⁹⁸ simulated the effect of IOL tilt and decentration with an IOL designed to fully correct an SA of 0.27 μm at a 6-mm aperture. For a 5-mm pupil, the IOL outperformed a spherical IOL at up to 7 degrees of tilt and 0.4-mm decentration.

A study by Baumeister et al²⁰³ compared the level of HOAs and simulated visual function parameters in patients in whom one eye received a Tecnis IOL and the other eye received the Sensar AR40e, a spherical IOL. Scheimpflug imagery determined mean IOL tilt and decentration to be less than 3 degrees and 0.3 mm, respectively. The simulation by Holladay et al¹⁹⁸ predicted the Tecnis IOL would improve visual function. However, although the Tecnis IOL did significantly reduce total HOA levels with 6.0-mm pupils, simulations with 6-mm pupils indicated that visual function with best spectacle correction was not significantly improved.

One explanation for this discrepancy is that the Holladay simulation¹⁹⁸ overestimated the benefit of the Tecnis IOL by assuming it would completely eliminate ocular SA through its negation of the average corneal SA. In reality, negating the average SA will leave many pseudophakic patients with significant residual SA if their preoperative SA is significantly different from the population average. The corneal SA in cataract patients ranges between 0.055 μm and 0.544 μm at 6 mm.¹⁹⁷

Also in doubt is the utility of correcting SA when many simulations have shown little to no expected benefit with 3-mm pupils. The 70-year-old pupil is approximately 2 mm smaller than the 20-year-old pupil.²⁰⁴ This helps reduce deterioration of visual quality with increased age and increased corneal and lenticular HOA. It also limits the benefit of SA correction with aspheric IOLs. One simulation²⁰⁴ estimated that for a patient with a 4-mm pupil, a centered spherical IOL, and full spectacle correction, fully neutralizing SA adds less benefit than would be gained by correcting 0.25 D of defocus. This potential benefit increases with increased pupil size, but with senile miosis it is unclear whether these effects are clinically significant.

All reviewed studies comparing spherical and aspheric IOLs found significantly lower ocular SA in eyes with an aspheric IOL. In studies comparing different aspheric IOLs^{205,206,207,208} the trend was for the residual SA at 6 mm with a Tecnis IOL to be approximately 0 μm, with the AcrySof IQ 0.1 μm and with the SofPort AO about 0.2 μm. Considering that the average corneal SA at 6 mm in the population is 0.27 μm^196,197,198 and the SA correction at 6 mm in the Tecnis (-0.27 μm), AcrySof IQ (-0.20 um), and SofPort AO (0) IOLs, these results are in line with preoperative expectations. It can be concluded that all three aspheric IOL strategies affect postoperative SA in the pseudophakic eye to the degree intended and significantly reduce SA in comparison with spherical IOLs.

Aspheric IOLs have also been shown to significantly reduce the magnitude of ocular HOAs compared with spherical IOLs but only at wider pupil diameters. This result is in line with expectations because the IOLs are designed to reduce only SA, and the magnitude of the SA correction is greater at larger aperture diameters where SA is larger and forms a greater proportion of total ocular HOA. In contrast, spherical IOLs increase ocular SA, especially at larger aperture diameters. This magnifies the difference between aspheric and spherical IOLs with larger pupils. Studies that compared the Tecnis, AcrySof IQ, and SofPort IOLs to each other^207,209 found no difference in HOA magnitude at any aperture diameter between 4 and 6 mm. Therefore, it is possible that the reduced HOA levels with aspheric IOLs are not due to the specific magnitude of SA correction in the aspheric IOL and rather caused by not implanting an HOA-inducing spherical IOL. Still the question remains, even if aspheric IOLs effectively reduce HOAs compared with spherical IOLs, do they provide any clinical benefit?

Nearly all reports in the literature have concluded that there is no evidence that aspheric IOLs improve visual acuity postoperatively.^{205,206,207,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235} Two papers did find a small but statistically significant best corrected visual acuity (BCVA) advantage in eyes implanted with the Tecnis 9000.^236,237 One of these compared the Tecnis 9000 to the Alcon SA60AT,²³⁷ a result not corroborated by another similar study that compared the same two IOLs.²¹⁶ Given the weight of evidence in the literature, it can be concluded that high-contrast photopic BCVA measurements are not significantly improved by implanting an aspheric IOL in the place of a standard spherical IOL.

Contrast sensitivity measurements, more than visual acuity, have been shown to predict functional vision and visual performance for a range of object scales. A significant improvement in contrast sensitivity might support the widespread implantation of aspheric IOLs despite the lack of evidence demonstrating improved visual acuity.

There is some evidence that aspheric IOLs slightly improve photopic contrast sensitivity, especially at lower spatial frequencies.^{216,225,229,234,236,237,238,239,240} Even if true, it is unclear if this small benefit would provide the average patient with any clinically significant improvement in quality of vision. Another point to consider is that at a luminance of 85 cd/m², where most of these photopic measurements were performed, the average pupil diameter was approximately 3 mm.^{205,213,219,222,225,232,237} At this level, aspheric IOLs have not been shown to significantly reduce ocular HOAs. If an improved HOA level is associated with improved visual function, it is more likely that improved contrast sensitivity will be conclusively found to occur at the larger pupil diameters induced by reduced lighting conditions.

Mesopic contrast sensitivity measurements performed at a median luminance of 3 to 6 cd/m² where the average pupil diameter in elderly pseudophakic patients is about 4 mm.^{205,219,225,226,228,232,236,237,241} At this larger pupil diameter there is more potential benefit in correcting SA as it induces a larger proportion of total HOAs. As expected by simulations, contrast sensitivity improved significantly under these conditions, with a large majority of studies^{212,218,224,225,226,227,229,231,232,234,236,237,238,239,240} showing a benefit for aspheric IOLs over spherical counterparts at one or more mainly lower spatial frequency.

Two studies compared patient satisfaction with aspheric and spherical IOLs. One²²⁸ compared subjective visual function in patients with bilaterally implanted Tecnis 9000 or AcrySof MA60AC IOLs and found no difference in Visual Function-14 scores. Another study²³⁰ compared the AcrySof IQ to the AcrySof SA60AT and found no statistically significant differences in vision-related quality of life with the National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25), despite significantly lower HOAs and SA levels in eyes with the aspheric IOL. The authors explained this discrepancy by stating that many in their patient population performed few tasks requiring highly functioning nighttime contrast sensitivity like night driving. More careful patient selection may have improved the subjective benefit enjoyed by trial subjects.

Peirs et al²⁴³ compared letter acuity and contrast sensitivity for two different values of SA in four young phakic patients with 4.8-mm pupils. The first condition was 0.154 μm of SA at a 4.8-mm pupil, the average amount of SA in pseudophakic patients with a spherical IOL, and the second condition was complete correction of the subject’s SA. Average contrast sensitivity improved 32% with complete negation of ocular SA. It should be noted that pupil size in these subjects was greater than that found in the average pseudophakic patient under all but scotopic conditions.^211,235 Therefore, the effect of negating SA in elderly pseudophakic patients is likely overestimated. However, the study does suggest that achieving a postoperative SA of 0 could have a clinically significant effect on contrast sensitivity under conditions where pupil size is larger.

It has also been suggested that targeting a postoperative SA of +0.10 at 6 mm is a better choice²⁴⁴ than targeting zero residual SA. This line of thinking is supported by Levy et al,²⁴⁵ who found a mean total SA of +0.110 ± 0.077 μm at 6 mm in 35 young patients with ‘supernormal’ vision (uncorrected visual acuity μ20/15). However, there is no logical basis for the implication that the patient’s SA was responsible for supernormal visual acuity. In fact, the authors found that the SA level in this population was comparable to a group of preoperative myopic patients considering refractive surgery (+0.128 ± 0.074 μm).²⁴⁶

Nevertheless, a trial by Beiko²⁴⁴ tested the theory of a postoperative SA of +0.10. He selected a group of patients with corneal SA greater than +0.33 um (average +0.370 ± 0.024 μm, range +0.337 to +0.411 μm) and implanted a Tecnis IOL with -0.27 μm of SA correction. The result in this group was compared to an unselected group of patients with an average preoperative corneal SA of +0.291 ± 0.081 μm at 6 mm (range +0.149 to +0.419 μm) who also received a Tecnis IOL. The first group demonstrated significantly better mesopic and photopic contrast sensitivity at multiple spatial frequencies. This interesting finding would need to be confirmed in a larger trial that compared visual function between groups targeting +0.10 or 0 residual ocular SA. This study does further support the notion that it is possible to target final ocular SA in a small group of patients.

It can also be argued that there is no single ideal target SA value, and that the optimal SA value depends on patient-specific factors. A study by Applegate et al²⁴⁷ examined the effect on visual acuity of combining various pairs of aberrations. They found that certain combinations of aberrations could improve letter acuity above the levels induced by either aberration alone. A report by Wang and Koch²⁴⁸ carried out a simulation examining the effect of varying ocular SA levels while leaving all other HOAs intact in 154 emmetropic eyes. Best image quality was obtained in more than 90% of eyes with a residual SA of between -0.05 and +0.05 μm. However, the specific pseudophakic ocular SA that optimized visual function depended on the interaction of many different corneal HOAs as well as pupil size.

Another point to consider is the potential benefits of residual SA. Increased ocular SA is associated with increased depth of focus^249,250 and improved distance corrected near visual acuity. With higher SA, fewer incoming rays converge at the focal point of the eye. Although this decreases optimum image quality at best focus, the off-center rays provide improved visual function at other points along the visual axis. When SA is corrected, fewer rays are focused at other points along the visual axis reducing depth of focus and distance corrected near acuity. The trade-off between optimized contrast sensitivity when SA is minimized and increased tolerance to defocus with higher residual SA should be considered when determining a patient’s ideal postoperative HOA profile.

The gold standard for cataract surgery patients has been to calculate for the intraocular lens power to emmetropia and leave the patients with a plano refraction so that they just need to wear reading glasses after surgery. This has been and still is a tremendously effective strategy that provides consistently excellent quality vision and stereopsis. But some patients do not want to wear reading glasses or bifocals even if the distance portion is close to plano. Monofocal IOLs, even in using a monovision strategy, are generally thought to provide better quality of vision and with fewer visual side effects than multifocal IOLs.²⁵⁷ Some clinicians use a minimonovision technique leaving the nondominant eye with a residual approximately -0.75 sphere to help with intermediate and near tasks. Properly selected and motivated patients can be happy and have good functional vision with a slightly greater difference. In one study²⁵⁸ with a mean anisometropia of 1.16 D, 96% of patients had better than 20/30 uncorrected distance visual vision acuity, and 92% had uncorrected near vision of J4 while maintaining good stereopsis s and contrast sensitivity. Another study found that for effective reading ability, monovision with the dominant eye left at plano and the nondominant eye left at -2.00 sphere provided satisfaction in 80% to 90% of properly selected cataract patients.²⁵⁹

A kind of monovision can also be achieved by implanting a multifocal IOL in one eye and a monofocal IOL in the other. One study found that unilateral implantation of a multifocal IOL (ReSTOR SN60D3) in patients who were previously pseudophakic with a monofocal IOL in the other eye, provided high levels of patient satisfaction (75%), spectacle freedom (65%), and good visual acuity without compromising contrast sensitivity.²⁶⁰ However, patients who received the multifocal IOLs bilaterally were more satisfied (92%) and had a greater level of spectacle freedom (77%).

Early attempts to manufacture a multifocal IOL were made by 3M Corporation in the 1980s through using a design similar to the current Tecnis (AMO) diffractive IOL based on diffractive lens technology across the entire anterior optic surface, similar to the current Tecnis (AMO) diffractive IOL. IOLAB Corporation, also in the early 1980s, fabricated a two-zone refractive bifocal disc IOL with a central near zone based in part on a design of Dr. John Pearce. Storz evaluated a three-zone refractive IOL in the mid-80s, and in 1989, Pharmacia introduced a multizonal IOL as well (Fig. 11-78). For these IOLs, the near zones of both designs were central and the distance portions peripheral.

In the 1980s, most IOLs were rigid and large incisions were used. Monofocal IOLs were giving good clinical results, and multifocal IOLs were evaluated on rigid IOL platforms in clinical studies. Similar designs evaluated as contact lenses generally had poor acceptance, and it was not clear at the time how good the multifocal IOL performance needed to be. There was no clear path to approval by either the U.S. FDA or the European regulatory agencies. In 1992, an FDA advisory panel approved the 3M diffractive multifocal IOL, but the FDA then requested that additional studies be conducted to evaluate vision while driving. Additional testing was done successfully, but the move to foldable IOLs in the mid-90s was then well under way, and the lens was never approved in the United States, though it was available for a while overseas. In 1997 Allergan Corporation’s Array lens was the first multifocal IOL to be approved by the FDA, following both conventional visual testing and a driving simulation evaluation.

Because of the superior performance of monofocal IOLs with regard to acuity performance, contrast sensitivity, and visual aberrations, multifocal technology was withdrawn from the U.S. market until 1997 when Allergan Corporation’s Array lens was approved by the FDA. This was the first multifocal design to be placed on a foldable IOL platform and was available until it was replaced by a similar multizonal refractive optic design created using a foldable hydrophobic material, which was designated the ReZoom IOL (AMO).

The Array lens by AMO was the first multifocal IOL to be FDA approved and marketed in the United States. It was a three-piece multifocal multizonal IOL manufactured from a second-generation silicone material (Fig. 11-79). The optic material had a refractive index of 1.46. It had angulated C-haptics made of extruded PMMA. The optical design of this lens was a zonal-progressive type with five concentric zones. It was a distance-dominant, zonal-progressive optic. The center of the lens was primarily for distance, with the other zones having distance and near vision in different proportions: 50% of the available light is devoted to distance vision, 37% to near vision, and it was suggested that 13% be directed to intermediate vision because of aspects of the design, and 37% to near vision. The addition for near vision is +3.5 D.

There were concerns related to a higher incidence of decreased contrast sensitivity, glare, and suboptimal near vision performance with the Array IOL. Due to the accommodative pupil constriction reflex, there was a concern that patients with smaller pupils might not benefit from the peripheral portions of the IOL devoted to near vision. However, Javitt and Steinert²⁶¹ compared bilateral implantation of the Array lens to a monofocal lens with respect to visual function, patient satisfaction, and quality of life. They found that those patients who had bilateral implantation with the Array obtained better uncorrected and distance-corrected near visual acuities and reported better overall vision, less limitation in visual function, and less spectacle dependency than patients with bilateral monofocal lenses. In a study by Schmitz et al²⁶² reporting on contrast sensitivity and glare disability with halogen light after monofocal and multifocal lens implantation, reduced contrast sensitivity was found in the multifocal group only at the lowest spatial frequency without halogen glare. The monofocal and multifocal groups of patients studied by Schmitz et al had no statistically significant differences in contrast sensitivity with moderate and strong glare.

The Array IOL reached a maximum popularity in 2000, with use in 35% to 50% of some ophthalmologists’ practice.