**8. Complications**

#### **8.1. Posterior capsular opacification (PCO)**

The most frequent long-term complication of cataract surgery remains posterior capsule opacification (PCO), an after cataract. In the past two decades, refinements in surgical technique and modifications in intraocular lens (IOL) design and material have led to a decrease in the incidence of PCO [102]. Symptoms of posterior capsule opacification include blurred vision and are similar to those of a normal cataract. Patients may also see streaks of light, halos, or excessive glare.

It has been shown that a sharp posterior optic edge inhibits migration of lens epithelial cells (LECs) behind the IOL optic and results in a lower incidence of PCO [103-106]. Most IOL designs, especially multipiece, have open-loop haptics that have a relatively narrow optic– haptic junction. The junction is thought to be an Achilles heel for LEC migration, and the narrower the junction, the better the optic-edge effect against LEC migration [106].

As intraocular lens (IOL) design [107, 108], the material [91, 109, 110], and the surgical technique [111, 112] play a crucial role in retarding the development of central posterior capsule opacification (PCO). Intraocular lens materials can be broadly divided into hydro‐ phobic and hydrophilic based on their surface energy. Acrylic IOLs with a hydrophobic or hydrophilic surface are widely used in practice [113, 114].Single-piece hydrophilic acrylic IOLs with a modified square edge are also available. The PCO rate with these hydrophilic IOLs, which have an improved 360-degree sharp edge, is reportedly lower than with older hydro‐ philic models that had a sharp optic edge design except at the optic–haptic junction [115].

Studies [113, 116] have compared PCO between older hydrophilic IOL models and single-piece hydrophobic acrylic IOLs, with the results favoring the latter. Because IOL characteristics play a crucial role in preventing PCO, it is important to assess PCO formation after implantation of these IOLs. This would help clinicians and researchers understand the impact of IOL material and design on the development of PCO.

Several studies report low PCO rates with square-edged IOLs and increased PCO with hydrophilic IOLs [117, 118]. However, both IOL material and design are important factors in the development of PCO.

The mechanism of action is hypothetically caused by a mechanical barrier effect of a sharp optic edge [106], by contact inhibition of the migrating LECs at the capsular bend by the square edge [107], and/or by the high pressure exerted by IOLs with a square-edged optic profile on the posterior capsule bend [108]. Based on these findings, various IOLs with often only minor differences in material and design were launched. With the introduction of 1-piece (monobloc) IOL designs, which are easier to implant and to manufacture, there was concern about a loss of the barrier effect to the migration of LECs in the region of the optic–haptic junction. The broad-based bulky haptics of 1-piece IOLs extending from the optic rim inherently interfere with capsular bag fusion, thus bending the posterior capsule. However, comparing 1- and 3 piece Acrysof IOLs, no statistically significant difference in PCO was found in the long run [103]. A study comparing two models of 1-piece hydrophilic acrylic IOLs showed significantly less PCO in the eyes with an IOL with a square edge across the optic–haptic junction than matched eyes with an IOL without a square edge at the junction 1 year after surgery [117]. For the most part, a square posterior optic edge has been considered the major factor in the prevention of PCO formation. Hydrophobic acrylic IOLs are not manufactured from the same materials or by using the same processes. Therefore, the polymers used differ in their chemical structure, water content, and refractive indices. Material differences are also reflected by the tendency toward glistening formation. Microvacuoles within the IOL material can occur when the IOL is in an aqueous environment and water fills microscopic openings in the material. Typical with acrylic IOLs, glistenings appear as white sparkling areas over the entire IOL optic, which may impair the optical quality. The higher density of the acrylic polymer network may prevent the formation of microvacuoles and provide better visual outcomes. Several studies conclude that hydrophobic IOLs are better than hydrophilic IOLs in preventing PCO [113, 116, 117].However, most comparisons have been between hydrophilic IOLs with round edges and hydrophobic IOLs with sharp edges.Regarding IOL design, the theory that an IOL with a sharp posterior optic edge prevents PCO has gained acceptance. There are two theories of how a sharp-edged optic inhibits PCO formation [103-105]. One is the compression theory, which suggests that contact pressure between the posterior capsule and the IOL optic edge mechan‐ ically prevents cell migration[103]. The other is that a sharp optic edge induces the formation of a sharp capsular bend, which creates contact inhibition between migrating lens epithelial cells (LECs) [104, 105]. Experimental and clinical studies suggest that the sharper the capsular bend, the greater the preventive effect [106]. Analysis of the microstructure of the optic edge of currently available square-edged hydrophilic and hydrophobic acrylic IOLs showed a large variation in the deviation from a perfect square, not only between IOL designs but also between different powers of the same IOL design.

presence of 1.00 D or higher astigmatism in eyes with a multifocal IOL compromise distance and near visual acuity, showing the importance of an optimal astigmatism correction in these

The most frequent long-term complication of cataract surgery remains posterior capsule opacification (PCO), an after cataract. In the past two decades, refinements in surgical technique and modifications in intraocular lens (IOL) design and material have led to a decrease in the incidence of PCO [102]. Symptoms of posterior capsule opacification include blurred vision and are similar to those of a normal cataract. Patients may also see streaks of

It has been shown that a sharp posterior optic edge inhibits migration of lens epithelial cells (LECs) behind the IOL optic and results in a lower incidence of PCO [103-106]. Most IOL designs, especially multipiece, have open-loop haptics that have a relatively narrow optic– haptic junction. The junction is thought to be an Achilles heel for LEC migration, and the

As intraocular lens (IOL) design [107, 108], the material [91, 109, 110], and the surgical technique [111, 112] play a crucial role in retarding the development of central posterior capsule opacification (PCO). Intraocular lens materials can be broadly divided into hydro‐ phobic and hydrophilic based on their surface energy. Acrylic IOLs with a hydrophobic or hydrophilic surface are widely used in practice [113, 114].Single-piece hydrophilic acrylic IOLs with a modified square edge are also available. The PCO rate with these hydrophilic IOLs, which have an improved 360-degree sharp edge, is reportedly lower than with older hydro‐ philic models that had a sharp optic edge design except at the optic–haptic junction [115].

Studies [113, 116] have compared PCO between older hydrophilic IOL models and single-piece hydrophobic acrylic IOLs, with the results favoring the latter. Because IOL characteristics play a crucial role in preventing PCO, it is important to assess PCO formation after implantation of these IOLs. This would help clinicians and researchers understand the impact of IOL material

Several studies report low PCO rates with square-edged IOLs and increased PCO with hydrophilic IOLs [117, 118]. However, both IOL material and design are important factors in

The mechanism of action is hypothetically caused by a mechanical barrier effect of a sharp optic edge [106], by contact inhibition of the migrating LECs at the capsular bend by the square edge [107], and/or by the high pressure exerted by IOLs with a square-edged optic profile on the posterior capsule bend [108]. Based on these findings, various IOLs with often only minor differences in material and design were launched. With the introduction of 1-piece (monobloc)

narrower the junction, the better the optic-edge effect against LEC migration [106].

patients [101].

194 Advances in Eye Surgery

**8. Complications**

light, halos, or excessive glare.

and design on the development of PCO.

the development of PCO.

**8.1. Posterior capsular opacification (PCO)**

The optic–haptic junction is another important factor in preventing PCO. In one study [105], eyes with an IOL with a continuous 360-degree square edge had significantly less PCO than eyes with an IOL with a square edge that was interrupted at the optic–haptic junction. Accordingly, it is hard to say which IOL has a proper design in terms of preventing PCO. It would be ideal for clinical PCO comparison studies to evaluate IOLs with the same material or design, although this would be difficult using currently available IOLs.

There are few studies comparing hydrophilic IOLs with a sharp edge and hydrophobic IOLs with a sharp edge [109, 113, 116]. In a study with a 2-year follow-up, Kugelberg et al. [109] found that patients with the Acrysof SA60AT hydrophobic acrylic IOL had less PCO than patients with the BL27 hydrophilic acrylic IOL (Bausch & Lomb). Others found no significant differences in the PCO and Nd:YAG rates between the hydrophobic group and hydrophilic group 3 years after surgery [113, 116].

Animal [119] and clinical [108] studies show that IOL design, rather than IOL material, is the critical factor in minimizing LEC migration across the posterior capsule after IOL implantation. The continuous-edge IOL has two design characteristics that may have led to the significant decrease in PCO, and that is a 360-degree continuous square optic edge, and greater space between the optic and haptic at the optic–haptic junction to encourage apposition of the anterior capsule and posterior capsule. A continuous square edge around the optic and angled haptics allows close apposition of the IOL optic to the posterior capsule, which Nishi et al. [120] found inhibits LEC migration. A rabbit model study [121] found that the addition of a square edge across the optic–haptic junction decreased LEC migration behind the IOL optic over migration with an IOL of the same type but without a square edge at the optic–haptic junction.

In the treatment of PCO, neodymium: yttrium-aluminum-garnet (ND:YAG) laser is used to cut the clouded posterior capsule allowing light to transmit normally [122]. It can produce complications such as ocular inflammation, an increase in intraocular pressure, IOL damage, cystoid macular edema, and retinal detachment.
