Fig. 24.1
Residual cell types after extracapsular cataract extraction. A cells: single-layer LECs around the anterior capsulorhexis opening; E cells: residual LECs located at the equator (lens bow)
After cataract surgery, disruption of the blood-aqueous barrier and surgical irritation stimulates an excessive increase in aqueous levels of various cytokines and growth factors, e.g., transforming growth factor-β (TGF-β), fibroblast growth factor (FGF)-2, interleukin-1(IL-1), IL-6, epidermal growth factor (EGF), and hepatocyte growth factor (HGF) [8]. Currently, TGF-β is considered the most important molecule causing the pathological fibrosis of LECs. The canonical Smad2/3 signaling activated by TGF-β is the first identified pathway of TGF-β-induced EMT, in which LECs are induced to transform into fibroblasts and produce excessive ECM [9, 10]. In addition to the canonical Smad signaling, other noncanonical signaling pathways activated by TGF-β, such as PI3K/AKT and ERK1/2 signaling, are also involved in the pathogenesis of PCO [11, 12]. Furthermore, previous studies also demonstrated that FGF-2 and HGF may stimulate massive proliferation LECs and that EGF promotes LEC migration [8]. Other studies reported that IL-1 not only stimulates LEC proliferation and ECM production but also exacerbates inflammation after cataract surgery [13]. Additionally, altered levels of growth factors are associated with disruption of blood-aqueous barrier, and therefore, in patients with preexisting conditions with disturbance to the blood-aqueous barrier, such as uveitis, the risk of developing PCO after surgery increseases [14].
24.2 Clinical Manifestations and Predisposing Factors of Pediatric Secondary Cataracts
24.2.1 Clinical Manifestations of Secondary Cataracts
The main symptom of secondary cataract is visual loss once again after cataract surgery. Slit-lamp examination reveals different morphologic types of PCO of varying severity (Fig. 24.2), including the following: (1) Soemmering ring (the regenerated peripheral cortical materials adhere to and are enveloped by the anterior and posterior capsules, forming a ring that is opaque at the periphery but transparent in the center), (2) pearl-type PCO (the retained E cells proliferate as clusters, forming transparent pearl-shaped bodies, also called Elschnig pearls), (3) fibrosis-type PCO (the residual A cells migrate toward the posterior capsule and secrete fibrous collagens, inducing fibrosis and producing folds and wrinkles in the posterior capsule), and (4) mixed type.
Fig. 24.2
Different morphological types of PCO. (a) Soemmering ring: the regenerated peripheral cortical materials adhere to and are enveloped by the anterior and posterior capsules (b) pearl-type PCO: the retained E cells proliferate as clusters, forming transparent pearl-shaped bodies (c) fibrosis-type PCO (the residual A cells migrate toward the posterior capsule producing folds and wrinkles in the posterior capsule (d) mixed-type PCO: posterior capsule opacification with two or more abovementioned characteristics
Among the various visual functions, secondary cataracts mainly affect visual acuity, contrast sensitivity, and glare sensitivity, depending on the type and the location of PCO. It has been shown that pearl-type PCO may exert a greater influence on central visual acuity, contrast sensitivity, and glare sensitivity across all spatial frequencies than fibrosis-type PCO [15].
24.2.2 Predisposing Factors for Secondary Cataracts
The incidence of pediatric secondary cataract is associated with multiple factors, including age at surgery, postoperative inflammatory response, surgical procedures or techniques, and the material, optic design, and implantation site of the intraocular lens (IOL) as well as the type of cataract.
24.2.2.1 Age at Surgery
The younger the age at surgery, the stronger the proliferative capacity of the residual LECs is. Even if posterior capsulotomy combined with anterior vitrectomy is performed during cataract surgery, there is still a high risk for developing secondary opacification. Peterseim and Wilson reported that, in cataract children undergoing posterior capsulectomy plus anterior vitrectomy, the risk of secondary cataracts was higher in children under the age of 2 months compared to older children [16]. In a study by Hosal, the relative risk for developing secondary cataracts in children younger than 1 year was 4.7 times that in older children [3].
24.2.2.2 Postoperative Inflammatory Response
Due to the surgical difficulties, the immaturity of blood-aqueous barrier, as well as the poor compliance with postoperative medications and follow-ups in children with cataracts, their postoperative inflammatory response is usually significant. The cytokine levels are abnormally high in the aqueous humor, creating an environment for the proliferation and EMT of LECs, which may promote the development of PCO.
24.2.2.3 Surgical Procedures
Today, the commonly used surgical procedure for pediatric cataracts includes phacoaspiration alone, phacoaspiration and posterior capsulotomy, and phacoaspiration and posterior capsulotomy together with anterior vitrectomy (AV). It has been shown that the first procedure has the highest incidence of PCO, while the third one has the lowest [3]. Children who did not receive posterior capsulotomy were five to ten times more likely to develop PCO than those who did [3]. Cataract extraction without posterior continuous curvilinear capsulorhexis (PCCC) or AV was associated with a PCO incidence of up to 76.9 %, surgery with PCCC but without AV was associated with an incidence of 44.4 %, while surgery with both PCCC and AV was associated with an incidence of only 11.8 % at 1–3 years of follow-up after surgery [17, 18]. Chrousos and colleagues reported that, in children with a small posterior capsulectomy opening, 12 % developed opacification, but when the opening was large enough, PCO was rarely seen [19]. In addition, surgical techniques may also affect the incidence of PCO. Skillful maneuvers and a short duration of surgery may help to avoid surgery-related injuries and disruption of the blood-aqueous barrier and thus reduce the risk of PCO.
24.2.2.4 Material, Design, and Implantation Site of the IOL
The risk of PCO also depends on whether or not an IOL is implanted. In pseudophakic eyes, the PCO incidence is correlated with the material, design, and implantation site of the IOL. Pseudophakic eyes of children are 3.6 times more likely to develop PCO than aphakic eyes [20].
The effect of the IOL material on the risk of PCO is mainly determined by its effect on LEC degeneration. The incidence of degeneration depends on the material of the implanted IOL; acrylic, PMMA, and silicone IOL are reported to be associated with incidences of LEC degeneration of 83 %, 15 %, and 8 %, respectively. This may be due to the fact that the hydrophobic property of the IOL material affects the adhesion between the IOL and capsule. The more hydrophobic the IOL material, the stronger the adhesion is with a higher risk of degeneration. The incidence of LEC degeneration is negatively correlated with the incidence of PCO [21].
The effect of IOL design on the risk of PCO mainly depends on its haptic and optic edge design. It has been well demonstrated in both experimental and clinical studies [22–24] that anterior optic-haptic angulation and a square-edged optic could effectively prevent the E cells on the posterior capsule from proliferating and migrating into the visual axis and thereby reduce the risk of PCO.
Besides, the implantation site of the IOL may also affect the incidence of PCO. Posterior capsulotomy combined with IOL optic capture reconstructs an anatomic barrier between the anterior and posterior segments and thus further decreases the incidence of PCO [25].
24.2.2.5 Type of Cataract
Some investigators have reported the surgical outcomes for congenital, developmental, and traumatic cataracts to be different and the incidence of PCO also varies [26]. Gimbel and colleagues reported that the cumulative incidence of conditions requiring posterior capsulectomy was higher in patients with traumatic cataracts compared to those with congenital cataracts over the age of 2 years [27]. The apparently increased incidence of PCO in traumatic cataracts may be due to a more severe inflammatory response following trauma.
24.2.2.6 Systemic Comorbidities
Certain systemic diseases such as juvenile idiopathic arthritis are also associated with a high incidence of secondary cataracts. BenEzra and Cohen [28] observed retrolental membranes in 80 % of patients aged 3–17 years with juvenile idiopathic arthritis despite posterior capsulotomy and anterior vitrectomy, all of whom required a second surgical intervention.
24.3 Prevention and Management of Pediatric Secondary Cataracts
In the 1960s, the preferred method of pediatric cataract surgery was lens aspiration, leaving the posterior capsule intact as popularized by Scheie. With this method, the residual LECs proliferate and migrate on the intact posterior capsule, giving rise to PCO. In some cases, the ensuing visual axial opacity causes greater visual impairment than the original cataract itself. After the introduction of vitrectomy in the 1970s, ophthalmic surgeons began to perform lens aspiration combined with posterior capsulotomy and anterior vitrectomy, and this new technique significantly decreased the incidence of secondary cataracts. In the early 1990s, application of phacoemulsification helped to reduce postoperative inflammatory response significantly, but the occurrence of PCO still led to poor vision. Secondary capsular opacification and fibrosis and shrinking of the capsular bag may be severe enough to cause IOL decentration and even break the optic-haptic junction. Even in the era of modern cataract surgery, pediatric secondary cataracts still pose a challenge for ophthalmologists.
24.3.1 Prevention of Pediatric Secondary Cataracts
24.3.1.1 Modifications of Surgical Techniques
When cataract aspiration with posterior capsulotomy alone is performed in pediatric cataract surgery, the intact anterior hyaloid membrane may still become a scaffold for the migration, proliferation, and transition of residual LECs. In order to further reduce the risk of PCO, the common practice is to perform cataract extraction combined with posterior capsulotomy and anterior vitrectomy. We suggest that anterior vitrectomy be performed in children younger than 3 years and the posterior capsule be left intact for children at 3 years or older as most older children can cooperate with Nd:YAG laser posterior capsulotomy under topical anesthesia.
A major advantage of cataract aspiration plus posterior capsulotomy and anterior vitrectomy is that it can decrease the incidence of secondary cataracts and laser posterior capsulotomy and its associated complications can be avoided [29]. However, posterior capsulotomy plus vitrectomy may increase the risk of cystoid macular edema, retinal detachment, and vitreous incarceration in the incision [30], whereas an intact posterior capsule may facilitate in-the-bag IOL implantation and also help to maintain the long-term stability of the implanted IOL.
There are two techniques for posterior capsulotomy: (1) vitrectorhexis via limbal or pars plana approach and (2) PCCC with capsulorhexis forceps or a radio-frequency diathermy device. After posterior capsulotomy, a posterior chamber IOL can be implanted in the capsular bag or in the ciliary sulcus. To ensure better centration of the IOL and reduce the risk of secondary cataracts, optic capture through the posterior capsule opening may be performed [31].
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