13.2.1 Glistenings and Nanoglistenings

Glistenings are fluid-filled microvacuoles (generally, 1–20 µm in diameter) that form within the IOL optic when the lens is in an aqueous environment (Fig. 13.1). Although they are largely described in association with hydrophobic acrylic IOLs, they can actually be observed with different IOL materials, including polymethyl methacrylate (PMMA). The majority of peer-reviewed articles on glistenings available in the literature describe them in relation to the AcrySof material (Alcon). ¹

The mechanism of glistening formation within IOLs has been evaluated and described in different studies. ^{1 ,​ 2} Polymers used for the manufacture of IOLs have different components, which may include different monomers, chromophores, and cross-linking agents, among others. Microvoids can be found within the network of polymers, depending on their architectural structure. Polymers generally absorb water when immersed in an aqueous environment for an extended time. The water absorption rate varies according to the IOL material, but for most of the currently available hydrophobic acrylic IOLs it is generally < 1%. The absorbed water is usually not visible because it is present in the form of water vapor within the polymer network. If the lens is placed in warm water and then the temperature is lowered, the water inside the polymer becomes oversaturated. The water surplus gathers inside the voids within the polymer network, forming glistenings. Because there is a significant difference in the refractive index of water droplets (1.33) and the bulk of the IOL polymer (e.g., 1.555 for AcrySof lenses), the light is refracted and scattered at the water–polymer interfaces, leading to a sparkling appearance of the fluid-filled vacuoles (thus the term glistenings).

Although it is difficult to compare different clinical studies due to differences in patient population and grading system used, among others, the majority of them show an increase in the incidence and/or severity of glistenings up to ~ 3 years postoperatively. ¹ One study following 12 eyes implanted with AcrySof lenses for 5 years showed stabilization of the degree of glistenings between 3 and 5 years, as indicated by light scattering within the IOL optic using Scheimpflug photography. ³ It is therefore reasonable to hypothesize that the incidence and degree of glistenings may increase until the IOL is completely hydrated and all available voids within the polymer network are visible as glistenings, under the influence of temperature fluctuations. Further long-term, prospective clinical studies are necessary to confirm this hypothesis. In terms of clinical impact, the majority of clinical studies show no influence on visual acuity, and there are few reports of a possible influence on contrast sensitivity, under specific test conditions. ¹ Review of the available literature and database mechanisms, such as Food and Drug Administration (FDA) reporting, revealed that explantation due to glistenings has been rarely reported, although underreporting of such cases remains a possibility. However, in the majority of these cases it has also been challenging to establish a direct relationship between the degree of glistenings and the patient symptoms leading to explantation.s. Literatur

Another hydration-related phenomenon that has been described in the literature in hydrophobic acrylic lenses is surface light scattering due to nanoglistenings (Fig. 13.2). Surface light scattering is a “whitening” appearance of the lens surface when the light is directed at the IOL at an angle of incidence of ≥ 30° during slit-lamp examination, or during image capture at an angle of 45° at Scheimpflug photography (Fig. 13.3). Some studies suggested that IOL light scattering was caused by a surface-bound biofilm. However, studies analyzing explanted lenses in dry and hydrated states, as well as analyses under cryofocused ion beam scanning electron microscopy (SEM) showed that scattering was predominantly caused by phase separation of water (from aqueous humor) as subsurface nanoglistenings. Surface light scattering/nanoglistenings have also been particularly studied and described in IOLs made of AcrySof material. ^{1 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8 ,​ 9}

Ogura et al analyzed the optical performance of cadaver-eye explanted AcrySof lenses with significant surface light scattering, as well as clinical explants removed at least 8.5 years after implantation. ⁶ The authors did not find any effect on image resolution, or on modulation transfer function values of the lenses. Although light transmittance was slightly decreased, the magnitude appeared to be inconsequential for optical performance. In another study, 49 single-piece AcrySof IOLs were obtained from human cadaver eyes (36 with blue light filter), and power/model matched to unused control IOLs. ⁷ Although surface light scattering of cadaver-eye removed lenses was significantly higher than that of controls and appeared to increase with time, no effect was observed on the light transmittance of single-piece hydrophobic acrylic lenses with or without a blue light filter. ⁷ Finally, clinical studies attempted to correlate surface light scattering with clinical complaints or effects on visual function, but to date no specific correlation was found. ^{8 ,​ 9}

13.2.2 Interlenticular Opacification

Interlenticular opacification (ILO) is mostly related to hydrophobic acrylic IOLs and is the opacification of the opposing surfaces of IOLs implanted in a piggyback manner. ^{10 ,​ 11 ,​ 12 ,​ 13} The purpose of implanting two or more posterior chamber IOLs (polypseudophakia or piggyback IOLs) is to (1) provide adequate pseudophakic optical correction for patients requiring high IOL power or (2) provide secondary correction of an undesirable optical result following cataract-IOL surgery. All cases analyzed in our laboratory appeared to be related to two posterior chamber IOLs implanted in the capsular bag through a small capsulorhexis, its margins overlapping the optic edge of the anterior IOL for 360°. ¹² All explanted lenses received were three-piece AcrySof IOLs. The adhesive nature of the acrylic material of this lens may play a role in the development of ILO. Opacification within the interlenticular space is derived from retained/regenerative cortex and pearls, with pathology similar to that of posterior capsule opacification (PCO).

Based on the common features of different cases of ILO, careful cortical clean up is mandatory in piggyback implantation. Surgical methods have been proposed for ILO prevention. The first is to implant both IOLs in the capsular bag with a relatively larger diameter capsulorhexis, and the second is to implant the anterior IOL in the sulcus and the posterior IOL in the bag with a small rhexis. In both scenarios, the lens epithelial cells within the equatorial fornix will be sequestered and will not have access to the interlenticular space.s. Literatur ^,​ s. Literatur ^{,​ 12}

13.3.1 Calcification

Postoperative optic opacification of modern hydrophilic acrylic IOL designs have been a significant complication leading to IOL explantation since 1999.s. Literatur ^{,​ 15} Different studies using histopathological, histochemical, electron microscopic, as well as elemental or molecular surface analytical techniques demonstrated that the opacification was related to calcium/phosphate precipitation on (Fig. 13.4) and/or within (Fig. 13.5) the lenses. ^{16 ,​ 17 ,​ 18 ,​ 19 ,​ 20} The four major designs manufactured in the United States and associated with the problem were the Hydroview (Bausch & Lomb), the MemoryLens (Ciba Vision), the SC60B-OUV (Medical Developmental Research), and the Aqua-Sense (Ophthalmic Innovations International). It is often difficult to determine the time at which optic opacification occurs, but lenses were, on average, explanted during the second year postimplantation. The opacification was not associated with anterior segment inflammatory reaction, and neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was ineffective in removing the calcified deposits from the lenses.

Calcification of hydrophilic acrylic lenses appears to be a multifactorial problem, and factors related to IOL manufacture, IOL packaging containing silicone compounds, surgical techniques and adjuvants, as well as patient metabolic conditions (e.g., diabetes), among others, may be implicated. Because the exact combination of factors and sequence of events ultimately leading to calcification of the lenses is still unknown, continuous research on this complication is warranted. This requires a multidisciplinary approach, which is further complicated by the fact that detailed manufacturing procedures are considered proprietary information, and some IOL designs are distributed in different countries with different commercial names. In the meantime, surgeons must be able to recognize this condition during clinical examination, to avoid performance of unnecessary procedures, such as Nd:YAG laser posterior capsulotomy (after a misdiagnosis of posterior capsule opacification), or vitrectomy (after a misdiagnosis of some form of vitreous opacity). We have described eight cases where calcification of the MemoryLens IOLs implanted was not recognized, with unnecessary procedures and repeated interventions ultimately leading to complications, such as retinal detachment and endophthalmitis. ²⁰ Explantation/exchange of the opacified/calcified IOL is to date the only possible treatment.