Ординатура / Офтальмология / Английские материалы / Refractive Lens Surgery_Fine, Packer, Hoffman_2005

14.7Complications

Surgical complications are expected to be similar for pseudo-accommodative IOLs as for monofocal IOLs, since the lenses are very similar and no modification to the surgical technique is necessary. If the postoperative refractive results are unsatisfactory for any reasons, a keratosurgical refinement procedure, e.g. LASIK or limbal relaxing incisions, may be considered in selected cases.

1.Hoffmann RS,Fine IH,Packer M (2003) Refractive lens exchange with a multifocal intraocular lens. Curr Opin Ophthalmol 14:24–30

2.Leyland M, Zinicola E (2003) Multifocal versus monofocal intraocular lenses in cataract surgery. A systemic review. Ophthalmology 110:1789–1798

3.Kohnen T, Kasper T (2005) Incision sizes before and after implantation of 6-mm optic foldable intraocular lenses using Monarch and Unfolder injector systems. Ophthalmology 112:58–66

4.Kohnen T (2004) Results of AcrySof ReSTOR apodized diffractive IOL in a European clinical trial. Joint meeting of the American Academy of Ophthalmology and European Society of Ophthalmology, Oct 2004, New Orleans, LA

The youthful, unaberrated human eye has become the standard by which we evaluate the results of cataract and refractive surgery today. Contrast sensitivity testing has confirmed the decline in visual performance with age, and wavefront science has helped explain that this decline occurs because of increasing spherical aberration of the human lens. Since we have learned that the optical wavefront of the cornea remains stable throughout life, the lens has started to come into its own as the primary locus for refractive surgery. At the same time, laboratory studies of accommodation have now confirmed the essentials of Helmholtz’s theory and have clarified the pathophysiology of presbyopia.What remains is for optical scientists and materials engineers to design an intraocular lens (IOL) that provides unaberrated optical imagery at all focal distances. This lens must, therefore, compensate for any aberrations inherent in the cornea and either change shape and location or employ multifocal optics.

Accommodative IOLs have now made their debut around the world (CrystaLens, Eyeonics and 1CU, HumanOptics). Clinical results indicate that restoration of accommodation can be achieved with axial movement of the lens optic [1]. However, concerns remain about the impact of long-term capsular fibrosis on the function of these designs. Flexible polymers designed for injection into a nearly intact capsular bag continue to show

promise in animal studies [2]. These lens prototypes require extraction of the crystalline lens through a tiny capsulorrhexis and raise concerns about leakage of polymer in the case of YAG capsulotomy following the development of posterior or anterior capsular opacification. A unique approach now in laboratory development involves the utilization of a thermoplastic acrylic gel, which may be shaped into a thin rod and inserted into the capsular bag (SmartLens, Medennium). In the aqueous environment at body temperature it unfolds into a full-size flexible lens that adheres to the capsule and may restore accommodation. Another unique design involves the light-adjustable lens, a macromer matrix that polymerizes under ultraviolet radiation (LAL, Calhoun Vision). An injectable form of this material might enable surgeons to refill the capsular bag with a flexible substance and subsequently adjust the optical configuration to eliminate aberrations.

While these accommodating designs show promise for both restoration of accommodation and elimination of aberrations, multifocal technology also offers an array of potential solutions. Multifocal intraocular lenses allow multiple focal distances independent of ciliary body function and capsular mechanics. Once securely placed in the capsular bag, the function of these lenses will not change or deteriorate. Additionally, multifocal lenses can be designed to take advantage of many innovations in IOL technology, which have

already improved outcomes, including better centration, prevention of posterior capsular opacification and correction of higher-order aberrations.

The fundamental challenge of multifocality remains preservation of optical quality, as measured by modulation transfer function on the bench or contrast sensitivity function in the eye, with simultaneous presentation of objects at two or more focal lengths. Another significant challenge for multifocal technology continues to be the reduction or elimination of unwanted photic phenomena, such as haloes. One question that the designers of multifocal optics must consider is whether two foci, distance and near, adequately address visual needs, or if an intermediate focal length is required. Adding an intermediate distance also adds greater complexity to the manufacture process and may degrade the optical quality of the lens.

We have been able to achieve success with the AMO Array multifocal IOL for both cataract and refractive lens surgery,largely because of careful patient selection [3]. We inform all patients preoperatively about the likelihood of their seeing haloes around lights at night, at least temporarily. If patients demonstrate sincere motivation for spectacle independence and minimal concern about optical side-effects, we consider them good candidates for the Array. These patients can achieve their goals with the Array, and represent some of the happiest people in our practice.

In the near future, the Array will likely become available on an acrylic platform, similar to the AMO AR40e IOL. This new multifocal IOL will incorporate the sharp posterior edge design (“Opti Edge”) likely to inhibit migration of lens epithelial cells. Prevention of posterior capsular opacification represents a special benefit to Array patients, as they suffer early deterioration in near vision with minimal peripheral changes in the capsule. AMO also plans to manufacture the silicone Array with a sharp posterior edge (similar to their Clariflex design).

The Array employs a zonal progressive refractive design. Alteration of the surface curvature of the lens increases the effective lens power and recapitulates the entire refractive sequence from distance through intermediate to near in each zone.A different concept of multifocality employs a diffractive design. Diffraction creates multifocality through constructive and destructive interference of incoming rays of light. An earlier multifocal IOL produced by 3M employed a diffractive design. It encountered difficulty in acceptance, not because of its optical design but rather due to poor production quality and the relatively large incision size required for its implantation.

Alcon is currently completing clinical trials of a new diffractive multifocal IOL based on the 6.0-mm foldable three-piece AcrySof acrylic IOL. The diffractive region of this lens is confined to the center,so that the periphery of the lens is identical to a monofocal acrylic IOL. The inspiration behind this approach comes from the realization that during near work the synkinetic reflex of accommodation, convergence and miosis implies a relatively smaller pupil size. Putting multifocal optics beyond the 3-mm zone creates no advantage for the patient and diminishes optical quality. In fact, bench studies performed by Alcon show an advantage in modulation transfer function for this central diffractive design, especially with a small pupil at near and a large pupil at distance (Figs. 15.1 and 15.2).

Recent advances in aspheric monofocal lens design may lend themselves to improvements in multifocal IOLs as well.We now realize that the spherical aberration of a manufactured spherical intraocular lens tends to worsen total optical aberrations. Aberrations cause incoming light that would otherwise be focused to a point to be blurred, which in turn causes a reduction in visual quality. This reduction in quality is more severe under low luminance conditions because spherical aberration increases when the pupil size increases.

The Tecnis Z9000 intraocular lens (AMO, Santa Ana,CA) has been designed with a modified prolate anterior surface to reduce or eliminate the spherical aberration of the eye. The Tecnis Z9000 shares basic design features with the CeeOn Edge 911 (AMO), including a 6-mm

biconvex square-edge silicone optic and angulated cap C polyvinylidene fluoride (PVDF) haptics. The essential new feature of the Tecnis IOL,the modified prolate anterior surface,compensates for average corneal spherical aberration and so reduces total aberrations in the eye.

Clinical studies show significant improvement in contrast sensitivity and functional vision with the new prolate IOL [4]. AMO plans to unite this foldable prolate design with their diffractive multifocal IOL currently available in Europe (811E) (Fig. 15.3). Improved visual performance and increased independence for patients constitute the fundamental concept behind this marriage of technologies. This new prolate, diffractive, foldable, multifocal IOL has received the CE mark in Europe. Introduction of the IOL in the USA will be substantially later. Food and Drug Administration-monitored clinical trials were expected to begin in the fourth quarter of 2004. Optical bench studies reveal superior modulation transfer function at both distance and near when compared to standard monofocal IOLs with a 5-mm pupil, and equivalence to standard monofocal IOLs with

a 4-mm pupil (Fig. 15.4). When compared to the Array multifocal IOL, the Tecnis IOL has better function for a small, 2-mm pupil at near and for a larger, 5-mm pupil at both distance and near (Fig. 15.5). From these studies, it appears that combining diffractive, multifocal optics with an aspheric, prolate design will enhance functional vision for pseudophakic patients.

Multifocal technology has already improved the quality of life for many pseudophakic patients by reducing or eliminating their need for spectacles. We (i.e., those of us over 40) all know that presbyopia can be a particularly maddening process. Giving surgeons the ability to offer correction of presbyopia by means of multifocal pseu- do-accommodation will continue to enhance their practices and serve their patients well.

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References

1.Doane J (2002) C&C CrystaLens AT-45 accommodating intraocular lens. Presented at the XX Congress of the ESCRS, Nice, Sept 2002

2.Nishi O, Nishi K (1998) Accommodation amplitude after lens refilling with injectable silicone by sealing the capsule with a plug in primates. Arch Ophthalmol 116:1358-1361

M.Packer · I. H. Fine · R. S. Hoffman

3.Packer M, Fine IH, Hoffman RS (2002) Refractive lens exchange with the Array multifocal intraocular lens. J Cataract Refract Surg 28: 421–424

4.Packer M, Fine IH, Hoffman RS, Piers PA (2002) Initial clinical experience with an anterior surface modified prolate intraocular lens. J Refract Surg 18:692–696

Robert J. Cionni

16.1Introduction

The normal human crystalline lens filters not only ultraviolet light, but also most of the higher frequency blue wavelength light. However, most current intraocular lenses (IOLs) filter only ultraviolet light and allow all blue wavelength light to pass through to the retina. Over the past few decades, considerable literature has surfaced suggesting that blue light may be one factor in the progression of age-related macular degeneration (AMD) [1]. In recent years, blue-light-filtering IOLs have been released by two IOL manufacturers. In this chapter we will review the motivation for developing blue-filtering IOLs and the relevant clinical studies that establish the safety and efficacy of these IOLs.

tistically significant higher prevalence of hard drusen and disciform scars than in agematched non-pseudophakic controls [4]. Pollack et al. [5] followed 47 patients with bilateral early AMD after they underwent extracapsular cataract extraction and implantation of a UV-blocking IOL in one eye,with the fellow phakic eye as a control for AMD progression. Neovascular AMD developed in nine of the operative versus two of the control eyes, which the authors suggested was linked to the loss of the “yellow barrier” provided by the natural crystalline lens.

Data from the Age-Related Eye Disease Study (AREDS), however, suggest a heightened risk of central geographic retinal atrophy rather than neovascular changes after cataract surgery [6, 7]. There were 342 patients in the AREDS study who were observed to have one or more large drusen or geo-

Even at the early age of 4 years, the human crystalline lens prevents ultraviolet and much of the high-energy blue light from reaching the retina (Fig. 16.1). As we age, the normal human crystalline lens yellows further, filtering out even more of the blue wavelength light [2]. In 1978, Mainster [3] demonstrated that pseudophakic eyes were more susceptible to retinal damage from near ultraviolet light sources. Van der Schaft et al. conducted postmortem examinations of 82 randomly selected pseudophakic eyes and found a sta-

cataract surgery. Cox regression analysis was used to compare the time to progression of AMD in this group versus phakic control cases matched for age, sex, years of follow-up, and course of AMD treatment. This analysis showed no increased risk of wet AMD after cataract surgery. However, a slightly increased risk of central geographic atrophy was demonstrated.

The retina appears to be susceptible to chronic repetitive exposure to low-radiance light as well as brief exposure to higher-radi- ance light [8–11]. Chronic, low-level exposure

(class 1) injury occurs at the level of the photoreceptors and is caused by the absorption of photons by certain visual pigments with subsequent destabilization of photoreceptor cell membranes. Laboratory work by Sparrow and coworkers has identified the lipofuscin component A2E as a mediator of blue-light damage to the retinal pigment epithelium (RPE) [12–15]; although the retina has inherent protective mechanisms from class 1 photochemical damage, the aging retina is less able to provide sufficient protection [16, 17].

Several epidemiological studies have concluded that cataract surgery or increased exposure of blue-wavelength light may be associated with progression of macular degeneration [18, 19]. Still, other epidemiologic studies have failed to come to this conclusion [20–22]. Similarly, some recent prospective trials have found no progression of diabetic retinopathy after cataract surgery [23, 24], while other studies have reported progression [25]. These conflicting epidemiological results are not unexpected, since both diabetic and age-related macular diseases are complex, multifactorial biologic processes. Certainly, relying on a patient’s memory to recall

the amount of time spent outdoors or in specific lighting environments over a large portion of their lifetime is likely to introduce error in the data. This is why experimental work in vitro and in animals has been important in understanding the potential hazards of blue light on the retina.

The phenomenon of phototoxicity to the retina has been investigated since the 1960s. But more recently, the effects of blue light on retinal tissues have been studied in more detail [8, 26–30]. Numerous laboratory studies have demonstrated a susceptibility of the RPE to damage when exposed to blue light [12, 31]. One of the explanations as to how blue light can cause RPE damage involves the accumulation of lipofuscin in these cells as we age. A component of lipofuscin is a compound known as A2E,which has an excitation maximum in the blue wavelength region (441 nm). When excited by blue light, A2E generates oxygen-free radicals, which can lead to RPE cell damage and death.At Columbia University, Dr Sparrow exposed cultured human retinal pigment epithelial cells laden with A2E to blue light and observed extensive cell death. She then placed different UV-

Fig. 16.2. Cultured human RPE cells laden with A2E exposed to blue wavelength light. Cell death is significant when UV-blocking colorless IOLs are

placed in the path of the light, yet is markedly reduced when the AcrySof Natural IOL is placed in the light path [32]

blocking IOLs or a blue-light-filtering IOL in the path of the blue light to see if the IOLs provided any protective effect. The results of this study demonstrated that cell death was still extensive with all UV-blocking colorless IOLs, but very significantly diminished with the blue-light-filtering IOL [32] (Fig. 16.2). Although these experiments were laboratory in nature and more concerned with acute light damage rather than chronic long-term exposure, they clearly demonstrated that by filtering blue light with an IOL, A2E-laden RPE cells could survive the phototoxic insult of the blue light.

16.3IOL Development

As a result of the mounting information on the effects of UV exposure on the retina [1, 33], in the late 1970s and early 1980s IOL manufacturers began to incorporate UVblocking chromophores in their lenses to protect the retina from potential damage. Still, when the crystalline lens is removed during cataract or refractive lens exchange surgery and replaced with a colorless UVblocking IOL,the retina is suddenly bathed in much higher levels of blue light than it has ever known and remains exposed to this increased level of potentially damaging light ever after. Yet, until recent years, the IOLmanufacturing community had not provided the option of IOLs that would limit the exposure of the retina to blue light. Since the early 1970s, IOL manufacturers have researched