CBS is a rare complication of cataract surgery.(9) Previous studies looked at CBS with slit lamp photography, and some with ultrasound biomicroscopy. This study is the first to comprehensively record CBS with anterior segment OCT. The cross-sectional image compiling multiple interference patterns from light reflected on the intraocular layers can better display the anterior segment image.(10) It can also be used to identify the slope and deflection of the intraocular lens optical region relative to the pupil plane(11) and sizing of the implantable collamer lens, indicating its accuracy and convenience.(12) Besides slit lamp examination, anterior segment OCT can help differentiate the substance lying between the intraocular lens and posterior capsule more clearly, compared with ultrasound biomicroscopy.
The categorization of CBS according to timing, clinical findings, mechanism and treatment is summarized in Table 3. Intraoperative CBS is caused by surgical manipulation during hydrodissection in cataract surgery. Acute CBS develops within two weeks following cataract surgery. Late CBS develops much later.
Previous classification of CBS was proposed by Kim et al.(13) They classified CBS into three groups according to their distinct clinical characteristics: noncellular, inflammatory, and fibrotic CBS. Noncellular CBS includes translucent fluid trapped in the posterior capsular bag. It is thought to be caused by retained viscoelastic materials and developed in the very early post-operative period. Inflammatory CBS is presented with prominent anterior chamber reaction in the early postoperative period and can be treated with anti-inflammatory medication. Fibrotic CBS is assumed to be caused by lens epithelial cell proliferation and pseudometaplasia. It is usually formed months to years after surgery. By definition, noncellular and inflammatory CBS belong to early CBS, and fibrotic CBS belongs to late CBS.
In our study, the four different types of CBS shown—minimally opaque, uniformly turbid, diffused sparkling, and focally condensed—indicate that the mechanism behind late CBS might vary. The distance between the posterior intraocular lens surface and posterior capsule ranged from 308 mm to 701 mm, implying that CBS might not be truly “fibrotic” as the bag could still be distended as deep as 701 mm. “Proliferative,” rather than “fibrotic,” is a better description for late CBS.
It is possible that the substances between the IOL and posterior capsular bag are different in the four groups and thus cause a distinct optical and refraction effect. The distended bag behind the intraocular lens forms a convex contour. The overall density and evenness of the substance in this convex contour may create various refractive effect, accounting for different refraction changes after Nd:YAG capsulotomy. The substance of the minimally opaque and diffused sparkling types may show even distribution and a refractive index mildly lower than vitreous and aqueous, so mild myopic refraction change was noted after laser capsulotomy. The materials in the uniformly turbid type also showed equal distribution, and they may create a higher or equal refractive index compared to those of vitreous and aqueous. Thus, this type of patient showed no or mild hyperopic refraction shift after laser treatment. In contrast, the substance in the focally condensed type may show an unequal distribution and a different refractive index from vitreous and aqueous, so absolute refraction change was significantly larger than the other groups.
According to the literature, late CBS can develop in a patient as young as seven years old. One such patient developed CBS four months after cataract surgery.(2) On the other hand, it can also develop in an 89-year-old patient who was found to have late CBS 20 years after surgery.(14) In our research, the ages range from 54 to 92, and the incubation time was between 15 and 136 months. Compared to acute CBS, late CBS does not lead to obvious visual manifestation such as vision change, refraction change, intraocular pressure elevation, or shallow anterior chamber.(15)
There are only a few studies documenting the axial length and intraocular lens design in CBS cases. Kim et al. believes that patients with longer axial length and an intraocular lens with four haptics are more likely to develop CBS.(13) Three piece,(16) trifocal toric,(17) accommodating(18) and hydrophylic(6) lenses were also reported. Our study reveals that most CBS patients have a normal axial length (23.63 ± 1.23 mm), and they were implanted with foldable one-piece hydrophobic lenses with two haptics. The intraocular lens dominance in this study might be due to local market preferences.
While the mechanism of intraoperative and acute CBS is well understood, the mechanism behind late CBS is still a mystery. The substance between the intraocular lens and posterior capsule might be different from that of acute CBS, as it causes only a few refraction changes or swelling of the ciliary body. Though some studies have posed a possibility of insidious infection such as Propionibacterium acnes,(3, 4) there has been no strong evidence presented to support this hypothesis. Raina et al.(19) performed a 25-gauge vitrectomy to get the specimen and culture. Both aerobic and anaerobic cultures yielded negative results for 14 days in three cases of late CBS. Rena et al. aspired the milky fluid and culture yielded no growth of any microbes.(5) In our study, we found no conjunctival congestion, corneal keratic precipitate, anterior chamber cells, plaque-like material coating around the intraocular lens, or flare-up of inflammation after YAG capsulotomy. Furthermore, we did not prescribe any antibiotics after YAG capsulotomy, but rather a low-dose topical steroid. In the event of indolent infection, there would be infection-associated inflammation after laser treatment, which results in the releasing of toxins and the infection source into the vitreous.
Another hypothesis for the mechanism of late CBS is lens epithelial cell proliferation. This can be supported by the slit lamp and anterior segment OCT images in our study, which showed focally condense materials in front of the posterior capsule (Fig 3). These materials may release fluid by self-degradation or drag turbid fluid inside the posterior capsular space by osmotic gradient. Nevertheless, some of the images showed few or no so-called proliferative materials around the posterior capsule (Figs 1 and 2). The diffused sparkling subtype CBS (Fig 4) indicates that there might be some other mechanism or substance inside that space. The hyper-reflective and diffusely distributed materials surprisingly do not affect vision according to our study results. The situation is similar in patients with asteroid hyalosis. The factors that determined which patient shows diffusely distributed particles, solutes or precipitate-like materials inside the capsular space are still mysteries.
Surgeons have taken the specimen between the capsular bag and intraocular lens for further analysis. Alpha-crystallin,(6, 7, 19) beta-crystallin,5 albumin,(7, 20) collagen,(19) calcium,(6) sodium hyruronate,(21) and globulin fractions(20) were found in the previous literature. Some of the substances were assumed to be released from lens epithelial cells.(19) These various results imply that there are different mechanisms behind capsular blockage syndrome formation. Different materials found in that space also explain why there are different types of presentation in anterior segment OCT.
Treatment of CBS includes anti-inflammatory medication for inflammatory CBS, Nd:YAG capsulotomy and surgical intervention. Gilhotra et al.(16) and Koh et al.(22) reported recurrence of CBS one week and 10 months after YAG capsulotomy, respectively. Capsular fluid aspiration(4, 5, 23) and vitrectomy(6) can be performed if laser treatment fails,(6) for refractory cases or cases that need specimens for analysis. All our patients, no matter which subtypes in anterior segment OCT, received laser capsulotomy without complications, and mean visual acuity improved 0.18 ± 0.09 on the LogMar.
The limitation of this study includes a small study number because this is a rare complication after cataract surgery. The case number might be underestimated as late CBS is usually asymptomatic, and thus medical help is typically not sought out. Some doctors might also overlook such cases as the clinical appearance is not obvious. The follow-up period in this study was only one month, unless patients had ocular disease such as dry eye, retinal problem, glaucoma, etc.