Role of fibronectin and IOL surface modification in IOL: Lens capsule interactions

Posterior Capsule Opacification (PCO) is one of the most common complications of cataract surgery. While studies have shown that IOL material properties and fibronectin adsorption may affect IOL-induced PCO in the clinical setting, the mechanism governing such interactions is not totally understood. Since strong adhesion forces between IOLs and posterior capsules (PCs) have been shown to impede cell infiltration and thus reduce PCO formation, this study was designed to assess whether fibronectin adsorption and IOL material properties would impact the IOL:PC adhesion force and cell infiltration using a PCO predictive in vitro model and a macromolecular dye imaging model, respectively. Our results showed that fibronectin adsorption significantly increased the adhesion forces and reduced simulated cell infiltration between acrylic foldable IOLs and the PC at physiological temperature in comparison to fibronectin-free controls. This fibronectin-mediated strong IOL: PC bond may be contributing to low PCO rates in the clinic for acrylic foldable IOLs. In addition, acrylic foldable IOLs coated with Di(ethylene glycol) (Diglyme), a hydrophilic coating known to reduce protein adsorption, was tested for its ability to alter adhesion force and cell infiltration. We observed that IOLs coated with Diglyme coating greatly reduced surface hydrophobicity and fibronectin adsorption of acrylic foldable IOLs. Furthermore, Diglyme coated IOLs showed significantly reduced adhesion force and increased simulated cell infiltration at the IOL:PC interface. The overall results support the hypothesis that IOL surface properties and their ability to adsorb fibronectin may have great impact on the IOL:PC adhesion force. A tight binding between IOLs and PC may contribute to the reduction of cell infiltration and thus the PCO incidence rate in the clinic.

Increased Desmosine in the lens capsules is associated with augmented elastin turnover in Pseudoexfoliation syndrome

Pseudoexfoliation syndrome (PXF) is an idiopathic disease with a high prevalence rate. The elastosis disorder is contributed by genetic and non-genetic factors. Elastin dysregulation associated with the disease mechanism is incompletely understood. This study evaluated the molecules of the elastogenesis machinery in PXF. Lens capsule and aqueous humor (aqH) samples (age/sex-matched) were collected from the eyes with PXF alone and PXF with glaucoma (PXF-G) undergoing Extra Capsular Cataract Extraction (ECCE) surgery. The Elastin turnover was assessed by estimating Desmosine levels in the lens capsules by HPLC analysis. Expression of elastogenesis genes [EMILIN1, CLU, FBN1, FN1, FBLN5, FBLN4 and LOXL1] were evaluated in the lens capsule by qPCR while the proteins were assessed in aqH by western blot analysis. The Desmosine content in the lens capsules were 3-fold and 6-fold elevated in PXF (P = 0.02) and PXF-G (P = 0.01) respectively compared to the cataract-alone, indicating increased elastin degradation. A significant increase in the transcript levels of the CLU, FBLN4, EMILIN1, FBLN5, FN1, FBN1, LOXL1 along with significant changes in protein expression of CLU, FBLN5, FBN1 and LOXL1 signified up-regulation of the elastogenesis machinery. The study provides direct evidence of augmented elastin degradation and turnover in the lens capsule of PXF marked by increased Desmosine content and the expression of proteins involved in mature elastin formation.

[Posterior YAG capsulotomy: selection of the application pattern]

BACKGROUND

The posterior neodymium-yttrium-aluminum-garnet laser capsulotomy is an established and simple method with a low complication rate for the treatment of secondary cataracts; however, the risk of intraocular pressure elevation, pit marks of the intraocular lens (IOL), anterior hyaloid damage, cystoid macular edema and retinal detachment may increase with high pulse number, pulse energy, and total energy.

PURPOSE

The optimization potential of the method through a rational choice of the laser pattern and the strategy, taking into account the mechanical properties of the posterior capsule and the anatomical features of the retrolental region, is shown.

MATERIAL AND METHODS

The article provides a literature review with own clinical observations and a geometric representation.

RESULTS

The efficiency of a laser pattern is examined with a constant capsulotomy length: The largest opening can be reached with the U‑pattern, which is followed by the +, T, H, V, O and spiral patterns in decreasing order. When estimating the size of the opening, its incircle is of particular functional importance. If the ability of the posterior capsule to tear spontaneously, which is predetermined by its anatomical and mechanical properties, is taken into account when choosing the application pattern and the laser strategy, the efficiency of the method increases.

CONCLUSION

An efficient technique is not only determined by an adapted defocusing and a minimum possible individual pulse energy setting but also characterized by the lowest possible total energy consumption if the necessary opening size is achieved by the smallest number of pulses. Taking into account the individual retrolental anatomical conditions and the mechanical properties of the NS membrane can contribute to the gentle implementation of a YAG capsulotomy.

Effect of time and temperature-dependent changes of IOL material properties on IOL: Lens capsule interactions

Posterior Capsule Opacification (PCO) is the most common complication associated with Intraocular Lens (IOL) implantation. Based on the assumption that the interactions between an IOL and the lens capsule (LC) may influence the extent of PCO formation, a new in vitro model was developed to quantify the adhesion force of an IOL to simulated LC using a custom-designed micro-force tester. Using this system, we examined the influence of temperature (room temperature vs. body temperature) and incubation time (0 vs. 24 h) on the adhesion force between IOLs and LCs. The results show that, in line with clinical observations of PCO incidence, the adhesion force increased at body temperature and with increase in incubation time in the following order, Acrylic foldable IOLs > Silicone IOLs > PMMA IOLs. By examining the changes of surface properties as a function of temperature and incubation time, we found that acrylic foldable IOLs showed the largest increase in their hydrophilicity and reported the lowest surface roughness in comparison to other IOL groups. Coincidentally, using a newly established macromolecular dye imaging system to simulate cell migration between IOLs and LC, we observed that the amount of macromolecular dye infiltration between IOLs and LCs was in the following order: PMMA IOLs > Silicone IOLs > Acrylic foldable IOLs. These results support a new potential mechanism that body temperature, incubation time, surface hydrophilicity and smoothness of IOLs greatly contribute to their tight binding to LCs and such tight binding may lead to reduced IOL: LC space, cell infiltration, and thus PCO formation.

Advanced glycation end products in human diabetic lens capsules

Advanced glycation end products (AGEs) accumulate with age in human lens capsules. AGEs in lens capsules potentiate the transforming growth factor beta-2-mediated mesenchymal transition of lens epithelial cells, which suggests that they play a role in posterior capsule opacification after cataract surgery. We measured AGEs by liquid chromatography-mass spectrometry in capsulorhexis specimens obtained during cataract surgery from nondiabetic and diabetic patients with and without established retinopathy. Our data showed that the levels of most AGEs (12 out of 13 measured) were unaltered in diabetic patients and diabetic patients with retinopathy compared to nondiabetic patients. There was one exception: glucosepane, which was significantly higher in diabetic patients, both with (6.85 pmol/μmol OH-proline) and without retinopathy (8.32 pmol/μmol OH-proline), than in nondiabetic patients (4.01 pmol/μmol OH-proline). Our study provides an explanation for the similar incidence of posterior capsule opacification between nondiabetic and diabetic cataract patients observed in several studies.

An in vitro system to investigate IOL: Lens capsule interaction

Posterior capsule opacification (PCO) is the most common complication associated with intraocular lens (IOL) implantation. Unfortunately, current in vitro models cannot be used to assess the potential of PCO due to their failure to simulate the posterior curvature of the lens capsule (LC) and IOL, a factor known to affect PCO pathogenesis in clinic. To overcome such a challenge, a new system to study IOL: LC interaction and potentially predict PCO was developed in this effort. It is believed that the interactions between an IOL and the lens capsule may influence the extent of PCO formation. Specifically, strong adhesion force between an IOL and the LC may impede lens epithelial cell migration and proliferation and thus reduce PCO formation. To assess the adhesion force between an IOL and LC, a new in vitro model was established with simulated LC and a custom-designed micro-force tester. A method to fabricate simulated LCs was developed by imprinting IOLs onto molten gelatin to create simulated three dimensional (3D) LCs with curvature resembling the bag-like structure that collapses on the IOL post implantation. By pushing the LC mold vertically downward, while measuring the change in position of the bending bar with respect to its start position, the adhesion force between the IOLs and LCs was measured. An in vitro system that can measure the adhesion force reproducibly between an IOL and LC with a resolution of ~1 μN was established in this study. During system optimization, the 10% high molecular weight gelatin produced the best LC with the highest IOL: LC adhesion force with all test lenses that were fabricated from acrylic foldable, polymethylmethacrylate (PMMA) and silicone materials. Test IOLs exerted different adhesion force with the 3D simulated LCs in the following sequence: acrylic foldable IOL > silicone IOL > PMMA IOL. These results are in good agreement with the clinical observations associated with PCO performance of IOLs made of the same materials. This novel in vitro system can provide valuable insight on the IOL: LC interplay and its relationship to clinical PCO outcomes.

Dynamics of the lens basement membrane capsule and its interaction with connective tissue-like extracapsular matrix proteins

The lens, suspended in the middle of the eye by tendon-like ciliary zonule fibers and facing three different compartments of the eye, is enclosed in what has been described as the thickest basement membrane in the body. While the protein components of the capsule have been a subject of study for many years, the dynamics of capsule formation, and the region-specific relationship of its basement membrane components to one another as well as to other matrix molecules remains to be explored. Through high resolution confocal and super-resolution imaging of the lens capsule and 3D surface renderings of acquired z-stacks, our studies revealed that each of its basement membrane proteins, laminin, collagen IV, nidogen and perlecan, has unique structure, organization, and distribution specific both to the region of the lens that the capsule is located in and the position of the capsule within the eye. We provide evidence of basal membrane gradients across the depth of the capsule as well as the synthesis of distinct basement membrane lamella within the capsule. These distinctions are most prominent in the equatorial capsule zone where collagen IV and nidogen span the capsule depth, while laminin and perlecan are located in two separate lamellae located at the innermost and outermost capsule domains. We discovered that an extracapsular matrix compartment rich in the connective tissue-like matrix molecules fibronectin, tenascin-C, and fibrillin is integrated with the superficial surface of the lens capsule. Each matrix protein in this extracapsular zone also exhibits region-specific distribution with fibrils of fibrillin, the matrix protein that forms the backbone of the ciliary zonules, inserting within the laminin/perlecan lamella at the surface of the equatorial lens capsule.

Clinical course of lens capsule fragment adherent to the posterior corneal surface after cataract surgery

PURPOSE

The purpose of the study was to evaluate the clinical features and outcomes of lens capsule fragment (LCF) adherent to the posterior corneal surface after cataract surgery. Methods A total of 12 eyes from 12 patients were included with a mean follow-up duration of 19.4 ± 12.6 months. Demographics and clinical features were collected by reviewing medical records and slitlamp photographs. Outcome parameters included corrected distance visual acuity (CDVA), central corneal thickness, and anterior segment optical coherence tomography (AS-OCT) features. Results All LCF located centrally and remained fixed and turned to semitransparent in a mean time of 28.7 ± 20.1 days. The AS-OCT revealed an extra membrane at the posterior corneal surface, with an underlying intact Descemet membrane in 9 eyes. All patients experienced corneal edema associated with LCF, which was medically managed and resolved in a mean time of 58.1 ± 40.2 days. CDVA improved from logarithm of minimum angle of resolution scores of 0.91 ± 0.63 preoperatively to 0.25 ± 0.18 at 2 months after surgery. None of the patients expressed subjective visual complaints. Conclusions LCF adherent to the posterior corneal surface caused prolonged corneal edema after cataract surgery, but exhibited no clinically significant complications in the midterm follow-up. AS-OCT provided useful diagnostics and differentiating features.

Altered stress field of the human lens capsule after cataract surgery

The lens capsule of the eye is important in focusing light onto the retina during the process of accommodation and, in later life, housing a prosthetic lens implanted during cataract surgery. Though considerable modeling work has characterized the mechanics of accommodation, little has been done to understand the mechanics of the lens capsule after cataract surgery. As such, we present the first 3-D finite element model of the post-surgical human lens capsule with an implanted tension ring and, separately, an intraocular lens to characterize the altered stress field compared to that in a model of the native lens capsule. All finite element models employed a Holzapfel hyperelastic constitutive model with regional variations in anisotropy. The post-surgical lens capsule demonstrated a dramatic perturbation to the stress field with mostly large reductions in stresses (except at the equator where the implant contacts the capsule) compared to native, wherein maximal changes in Cauchy stress were -100% and -145% for the tension ring and intraocular lens, respectively. However, implantation of the tension ring produced a more uniform stress field compared to the IOL. The magnitudes and distribution of the perturbed stress field may be an important driver of the fibrotic response of inhabiting lens epithelial cells and associated lens capsule remodeling after cataract surgery. Thus, the mechanical effects of an implant on the lens capsule could be an essential consideration in the design of intraocular lenses, particularly those with an accommodative feature.

Mechanical properties of anterior lens capsule assessed with AFM and nanoindenter in relation to human aging, pseudoexfoliation syndrome, and trypan blue staining

The purpose of this study is the mechanical characterization of the mid-to- old-age human anterior lens capsules (ALCs) obtained by capsulorhexis using Atomic Force Microscopy (AFM) and a nanoindenter at different spatial scales. The dependencies on the human age, presence or absence of pseudoexfoliation syndrome (PEX), and application of trypan blue staining during the surgery were analyzed. The measurements on both the anterior (AS) and epithelial (ES) sides of the ALC were conducted and the effect of cells present on the epithelial side was carefully accounted for. The ES of the ALC had a homogenous distribution of the Young's modulus over the surface as shown by the macroscale mapping with the nanoindenter and local AFM indentations, while the AS was more heterogeneous. Age-related changes were assessed in groups ranging from the mid-age (from 48 years) to old-age (up to 93 years). We found that the ES was always stiffer than the AS, and this difference decreased with age due to a gradual decrease in the Young's modulus of the ES and an increase in the modulus of the AS. No significant changes were found in the mechanical properties of ALCs of PEX patients versus the PEX-free group, as well as in the properties of the ALC with and without trypan blue staining.

Lysyl hydroxylase 3 is required for normal lens capsule formation and maintenance of lens epithelium integrity and fate

Lens abnormalities are a major cause of reduced vision and blindness. One mechanism that can lead to reduced lens transparency, i.e. cataract, is abnormal behavior of lens epithelial cells (LECs), the precursors of the transparent lens fiber cells. Here we describe a zebrafish mutation causing the embryonic lens epithelium to generate cellular masses comprising partially differentiated lens fiber cells. We identify the mutant gene as plod3, which encodes for Lysyl hydroxylase 3 (Lh3), an enzyme essential for modification of collagens, including Collagen IV, a main component of the lens capsule. We show that plod3-deficient lenses have abnormal lens epithelium from an early developmental stage, as well as abnormal lens capsules. Subsequently, upregulation of TGFβ signaling takes place, which drives the formation of lens epithelial cellular masses. We identify a similar phenotype in Collagen IVα5-deficient embryos, suggesting a key role for the defective lens capsule in the pathogenesis. We propose that plod3 and col4a5 mutant zebrafish can serve as useful models for better understanding the biology of LECs during embryonic development and in formation of lens epithelium-derived cataract.

Effect of intraoperative trypan blue on lens epithelial cells - Histomorphological analysis

Introduction

Trypan Blue is an acid azo dye commonly used as a stain to distinguish viable from non-viable cells. It is a vital stain used intra operatively during cataract surgery to stain the external surface of the anterior lens capsule for better visualization.

Aim

To analyze the histomorphological effects of trypan blue on Lens Epithelial cells and the Basement Membrane on direct exposure by staining the internal surface of the anterior lens capsule during Small Incision Cataract Surgery.

Methods

Analytical cross sectional case control study. Anterior capsule specimens of 14 Patients undergoing small incision cataract surgery at Department of Ophthalmology, Govt Medical College Hospital, Thrissur were studied. Two specimens of anterior capsule taken from the same eye form the case and control. Control specimen (sample A) was removed first, after the routine external staining with trypan blue 0.06% (w/v) for 10 seconds. The stain was washed off by balanced salt solution in every case. Then trypan blue was injected under the remaining anterior capsule and case (Test) specimen (sample B) was obtained after direct contact of trypan blue to the internal surface (lens epithelial cells) for 1 minute. Histomorphological (qualitative and quantitative) examination of both specimens done.

Results

Qualitative data analysis was done by EPI INFO software.v.7. Intactness of LECs throughout the length was statistically significant in Sample A (p = 0.000027). Partial and complete detachment of Lens Epithelial Cells, degeneration, and nuclear smudging were significantly higher in Sample B. Qualitative analysis of the basement membrane showed significant edema of the basement membrane in sample B. Basement membrane splitting observed in sample B was not statistically significant. Quantitative data analyzed using independent t test. There was a statistically significant decrease in cell density in sample B with p value less than 0.05.

Discussion

Our study demonstrated that direct staining of the internal surface of anterior capsule with trypan blue affected LECs and the basement membrane. There were reduction in cell density, irreversible degeneration of Lens Epithelial Cells and basement membrane edema. Hence treating the internal surface of capsular bag with trypan blue may reduce incidence of Posterior capsular opacification.

Anterior lens capsule strains during simulated accommodation in porcine eyes

Experimental protocols have been developed to measure the spatial variation of the mechanical strains induced in the lens capsule during ex vivo lens stretching. The paper describes the application of these protocols to porcine lenses. The deformations and mechanical strains developed in the anterior capsule during each experiment were determined using full field digital image correlation techniques, by means of a speckle pattern applied to the lens surface. Several speckling techniques and illumination methods were assessed before a suitable combination was found. Additional data on the cross section shape of the anterior lens surface were obtained by Scheimpflug photography, to provide a means of correcting for lens curvature effects in the determination of the strains developed in the plane of the capsule. The capsule strains in porcine lenses exhibit non-linear behaviour, and hysteresis during loading and unloading. Peripheral regions experience higher magnitude strains than regions near the lens pole. The paper demonstrates the successful application of a procedure to make direct measurements of capsule strains simultaneously with ex vivo radial lens stretching. This experimental technique is applicable to future investigations on the mechanical characteristics of human lenses.

Adamts18 deletion results in distinct developmental defects and provides a model for congenital disorders of lens, lung, and female reproductive tract development

The ADAMTS family comprises 19 secreted metalloproteinases that cleave extracellular matrix components and have diverse functions in numerous disease and physiological contexts. A number of them remain 'orphan' proteases and among them is ADAMTS18, which has been implicated in developmental eye disorders, platelet function and various malignancies. To assess in vivo function of ADAMTS18, we generated a mouse strain with inactivated Adamts18 alleles. In the C57Bl6/Ola background, Adamts18-deficient mice are born in a normal Mendelian ratio, and are viable but show a transient growth delay. Histological examination revealed a 100% penetrant eye defect resulting from leakage of lens material through the lens capsule occurring at embryonic day (E)13.5, when the lens grows rapidly. Adamts18-deficient lungs showed altered bronchiolar branching. Fifty percent of mutant females are infertile because of vaginal obstruction due to either a dorsoventral vaginal septum or imperforate vagina. The incidence of ovarian rete is increased in the mutant mouse strain. Thus, Adamts18 is essential in the development of distinct tissues and the new mouse strain is likely to be useful for investigating ADAMTS18 function in human disease, particularly in the contexts of infertility and carcinogenesis.