Current State of the Art and Next Generation of Materials for a Customized IntraOcular Lens according to a Patient-Specific Eye Power

How do intraocular lens materials influence the outcome of cataract surgery?

PURPOSE OF REVIEW

This review summarizes the evidence on the effect of intraocular lens (IOL) material on the outcomes of cataract surgery, as well as on the surgical procedure itself.

RECENT FINDINGS

Differences in capsular biocompatibility between IOL materials lead to variations in capsular stability and posterior capsule opacification (PCO), while differences in uveal biocompatibility affect postoperative inflammatory response.

SUMMARY

Refractive outcomes are affected by both incision size and the rotational stability of toric IOLs. Small incision sizes favour hydrophilic IOLs. Rotational stability of hydrophobic and hydrophilic IOLs were comparable in recent studies. Visual outcomes are affected by chromatic aberrations, dysphotopsia, lens opacifications and PCO. Hydrophilic IOLs are associated with reduced chromatic dispersion. Hydrophobic IOL opacifications are caused by sub-surface glistenings, while hydrophilic IOL opacifications are due to surface calcifications. Some surgeries, including pars plana vitrectomy and lamellar corneal transplants, were shown to increase the risk of IOL calcifications, although the mechanism is still unknown. Hydrophilic IOLs have greater ease of manipulation, greater resistance to IOL damage, and higher uveal biocompatibility. Hydrophobic IOLs show better PCO prevention than hydrophilic IOLs, and should be preferred in highly myopic eyes where Nd:YAG capsulotomy might increase the risk of retinal detachment.

Innovative Polymeric Biomaterials for Intraocular Lenses in Cataract Surgery

Intraocular lenses (IOLs) play a pivotal role in restoring vision following cataract surgery. The evolution of polymeric biomaterials has been central to addressing challenges such as biocompatibility, optical clarity, mechanical stability, and resistance to opacification. This review explores essential requirements for IOL biomaterials, emphasizing their ability to mitigate complications like posterior capsule opacification (PCO) and dysphotopsias while maintaining long-term durability and visual quality. Traditional polymeric materials, including polymethyl methacrylate (PMMA), silicone, and acrylic polymers, are critically analyzed alongside cutting-edge innovations such as hydrogels, shape memory polymers, and light-adjustable lenses (LALs). Advances in polymer engineering have enabled these materials to achieve enhanced flexibility, transparency, and biocompatibility, driving their adoption in modern IOL design. Functionalization strategies, including surface modifications and drug-eluting designs, highlight advancements in preventing inflammation, infection, and other complications. The incorporation of UV-blocking and blue-light-filtering agents is also examined for their potential in reducing retinal damage. Furthermore, emerging technologies like nanotechnology and smart polymer-based biomaterials offer promising avenues for personalized, biocompatible IOLs with enhanced performance. Clinical outcomes, including visual acuity, contrast sensitivity, and patient satisfaction, are evaluated to provide an understanding of the current advancements and limitations in IOL development. We also discuss the current challenges and future directions, underscoring the need for cost-effective, innovative polymer-based solutions to optimize surgical outcomes and improve patients' quality of life.

Examining Penetration and Residual Depth in Modern Acrylic Foldable Intraocular Lenses: A Laboratory Study Using Differential Interference Contrast Microscopy to Compare Hydrophilic and Hydrophobic Materials

Introduction The material of modern intraocular lenses must meet the highest standards and fulfill various requirements. It is crucial that the material shows the best biocompatibility and should be flexible for an uncomplicated implantation process through small corneal incisions but also sufficiently rigid for good stability and centering in the capsular bag. In addition, the optic must remain clear for life and retain the best optical properties. Methods In this laboratory experiment, we performed scratch tests for the mechanical assessment of acrylic intraocular lenses. The aim was to determine differences in the behavior in regard to the manufacturing process and water content of hydrophilic and hydrophobic acrylic intraocular lenses. The scratch tests were performed using a Nano Scratch Tester. A conical indenter with a tip radius of 1 µm and a cone angle of 90° was selected to scratch the samples at three different constant loads of 5, 10, and 15 mN, respectively. The scratch length was set to 100 µm at a scratch speed of 200 µm/min. Hydrophilic and hydrophobic acrylic intraocular lenses (with different water content) were tested. Results The results showed that for sample A (hydrophilic acrylate), the penetration depth increases steadily with increasing force from 25-30 µm (5 mN) to 28-33 µm (10 mN) and 34-37 µm (15 mN). The penetration depths during the scratches seem to be load-dependent. In sample B (hydrophobic acrylate), the same forces lead to steadily increasing penetration depths: 25-30 µm (5 mN), 40-44 µm (10 mN), and 54-57 µm (15 mN). The evaluation of the residual depth showed much lower values for all samples. In the hydrophilic, softer samples (A), the residual depth was between 1 µm and 4 µm. In the hydrophobic, more solid, samples (B), the residual depth was more pronounced with values between 5 µm and 17 µm. The plastic influence and deformation zone seemed to be wider for the hydrophobic samples than for the hydrophilic samples. Conclusion The laboratory experiment confirms that modern, acrylic intraocular lenses are sensitive to scratches/touch, and penetration depths during scratching depend on the load. The remaining depths after the scratches are significantly lower and show a load dependence. The deforming zone was higher in the hydrophobic acrylates than in the hydrophilic acrylates. However, the results confirm that damage can occur with hydrophobic and hydrophilic acrylic materials, depending on the force applied. Therefore, careful handling during the preparation and implantation process is crucial to prevent permanent defects.

BCLA CLEAR presbyopia: Management with intraocular lenses

Cataract surgery including intraocular lens (IOL) insertion, has been refined extensively since the first such procedure by Sir Harold Ridley in 1949. The intentional creation of monovision with IOLs using monofocal IOL designs has been reported since 1984. The first reported implantation of multifocal IOLs was published in 1987. Since then, various refractive and or diffractive multifocal IOLs have been commercialised. Most are concentric, but segmented IOLs are also available. The most popular are trifocal designs (overlaying two diffractive patterns to achieve additional focal planes at intermediate and near distances) and extended depth of focus designs which leave the patient largely spectacle independent with the reduced risk of bothersome contrast reduction and glare. As well as mini-monovision, surgical strategies to minimise the impact of presbyopia with IOLs includes mixing and matching lenses between the eyes and using IOLs whose power can be adjusted post-implantation. Various IOL designs to mimic the accommodative process have been tried including hinge optics, dual optics, lateral shifts lenses with cubic-type surfaces, lens refilling and curvature changing approaches, but issues in maintaining the active mechanism with post-surgical fibrosis, without causing ocular inflammation, remain a challenge. With careful patient selection, satisfaction rates with IOLs to manage presbyopia are high and anatomical or physiological complications rates are no higher than with monofocal IOLs.

Application of Silicone in Ophthalmology: A Review

This paper reviews the latest trends and applications of silicone in ophthalmology, especially related to intraocular lenses (IOLs). Silicone, or siloxane elastomer, as a synthetic polymer, has excellent biocompatibility, high chemical inertness, and hydrophobicity, enabling wide biomedical applications. The physicochemical properties of silicone are reviewed. A review of methods for mechanical and in vivo characterization of IOLs is presented as a prospective research area, since there are only a few available technologies, even though these properties are vital to ensure medical safety and suitability for clinical use, especially if long-term function is considered. IOLs represent permanent implants to replace the natural lens or for correcting vision, with the first commercial foldable lens made of silicone. Biological aspects of posterior capsular opacification have been reviewed, including the effects of the implanted silicone IOL. However, certain issues with silicone IOLs are still challenging and some conditions can prevent its application in all patients. The latest trends in nanotechnology solutions have been reviewed. Surface modifications of silicone IOLs are an efficient approach to further improve biocompatibility or to enable drug-eluting function. Different surface modifications, including coatings, can provide long-term treatments for various medical conditions or medical diagnoses through the incorporation of sensory functions. It is essential that IOL optical characteristics remain unchanged in case of drug incorporation and the application of nanoparticles can enable it. However, clinical trials related to these advanced technologies are still missing, thus preventing their clinical applications at this moment.

Biopolymeric Innovations in Ophthalmic Surgery: Enhancing Devices and Drug Delivery Systems

The interface between material science and ophthalmic medicine is witnessing significant advances with the introduction of biopolymers in medical device fabrication. This review discusses the impact of biopolymers on the development of ophthalmic devices, such as intraocular lenses, stents, and various prosthetics. Biopolymers are emerging as superior alternatives due to their biocompatibility, mechanical robustness, and biodegradability, presenting an advance over traditional materials with respect to patient comfort and environmental considerations. We explore the spectrum of biopolymers used in ophthalmic devices and evaluate their physical properties, compatibility with biological tissues, and clinical performances. Specific applications in oculoplastic and orbital surgeries, hydrogel applications in ocular therapeutics, and polymeric drug delivery systems for a range of ophthalmic conditions were reviewed. We also anticipate future directions and identify challenges in the field, advocating for a collaborative approach between material science and ophthalmic practice to foster innovative, patient-focused treatments. This synthesis aims to reinforce the potential of biopolymers to improve ophthalmic device technology and enhance clinical outcomes.

Lens epithelial cell response to polymer stiffness and polymer chemistry

Posterior capsule opacification (PCO) is the most common complication of cataract surgery, and intraocular lens (IOL) implantation is the standard of care for cataract patients. Induction of post-operative epithelial-mesenchymal transition (EMT) in residual lens epithelial cells (LEC) is the main mechanism by which PCO forms. Previous studies have shown that IOLs made with different materials have varying incidence of PCO. The aim of this paper was to study the interactions between human (h)LEC and polymer substrates. Polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxypropyl tris (trimethylsiloxy) silane (TRIS) were synthesized and evaluated due to the clinical use of these materials as ocular biomaterials and implants. The chemical properties of the polymer surfaces were evaluated by contact angle, and polymer stiffness and roughness were measured using atomic force microscopy. In vitro studies showed the effect of polymer mechanical properties on the behavior of hLECs. Stiffer polymers increased α-smooth muscle actin expression and induced cell elongation. Hydrophobic and rough polymer surfaces increased cell attachment. These results demonstrate that attachment of hLECs on different surfaces is affected by surface properties in vitro, and evaluating these properties may be useful for investigating prevention of PCO.

Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bonds

Four amino acid-bearing acrylamides, N-acryloyl-l-threonine (AThrOH), N-acryloyl-l-glutamic acid (AGluOH), N-acryloyl-l-phenylalanine (APheOH), and N-acryloyl-l, l-diphenylalanine (APhePheOH), were selected for copolymerization with n-butyl acrylate (nBA) to develop amino acid-based self-healable copolymers. A series of copolymers comprising amino acid-bearing acrylamides and nBA with tunable comonomer compositions and molecular weights were synthesized by free radical and reversible addition-fragmentation chain-transfer copolymerization. Self-healing and mechanical properties originated from the noncovalent bonds between the carboxyl, hydroxyl, and amide groups, and π-π stacking interactions among the amino acid residues in the side chains were evaluated. Among these copolymers, P(nBA-co-AGluOH) with suitable comonomer compositions and molecular weights (nBA : AGluOH = 82 : 18, Mn = 18 300, Mw/Mn = 2.58) exhibited good mechanical properties (modulus of toughness = 17.3 MJ m-3) and self-healing under ambient conditions. The multiple noncovalent bonds of P(nBA-co-AGluOH)s were also efficient in improving the optical properties with an enhanced refractive index and good transparency.

Hydrogels in Ophthalmology: Novel Strategies for Overcoming Therapeutic Challenges

The human eye's intricate anatomical and physiological design necessitates tailored approaches for managing ocular diseases. Recent advancements in ophthalmology underscore the potential of hydrogels as a versatile therapeutic tool, owing to their biocompatibility, adaptability, and customizability. This review offers an exploration of hydrogel applications in ophthalmology over the past five years. Emphasis is placed on their role in optimized drug delivery for the posterior segment and advancements in intraocular lens technology. Hydrogels demonstrate the capacity for targeted, controlled, and sustained drug release in the posterior segment of the eye, potentially minimizing invasive interventions and enhancing patient outcomes. Furthermore, in intraocular lens domains, hydrogels showcase potential in post-operative drug delivery, disease sensing, and improved biocompatibility. However, while their promise is immense, most hydrogel-based studies remain preclinical, necessitating rigorous clinical evaluations. Patient-specific factors, potential complications, and the current nascent stage of research should inform their clinical application. In essence, the incorporation of hydrogels into ocular therapeutics represents a seminal convergence of material science and medicine, heralding advancements in patient-centric care within ophthalmology.

From Static to Dynamic: Smart Materials Pioneering Additive Manufacturing in Regenerative Medicine

The emerging field of regenerative medicine holds immense promise for addressing complex tissue and organ regeneration challenges. Central to its advancement is the evolution of additive manufacturing techniques, which have transcended static constructs to embrace dynamic, biomimetic solutions. This manuscript explores the pivotal role of smart materials in this transformative journey, where materials are endowed with dynamic responsiveness to biological cues and environmental changes. By delving into the innovative integration of smart materials, such as shape memory polymers and stimulus-responsive hydrogels, into additive manufacturing processes, this research illuminates the potential to engineer tissue constructs with unparalleled biomimicry. From dynamically adapting scaffolds that mimic the mechanical behavior of native tissues to drug delivery systems that respond to physiological cues, the convergence of smart materials and additive manufacturing heralds a new era in regenerative medicine. This manuscript presents an insightful overview of recent advancements, challenges, and future prospects, underscoring the pivotal role of smart materials as pioneers in shaping the dynamic landscape of regenerative medicine and heralding a future where tissue engineering is propelled beyond static constructs towards biomimetic, responsive, and regenerative solutions.

A proposed model of xeno-keratoplasty using 3D printing and decellularization

Corneal opacity is a leading cause of vision impairment and suffering worldwide. Transplantation can effectively restore vision and reduce chronic discomfort. However, there is a considerable shortage of viable corneal graft tissues. Tissue engineering may address this issue by advancing xeno-keratoplasty as a viable alternative to conventional keratoplasty. In particular, livestock decellularization strategies offer the potential to generate bioartificial ocular prosthetics in sufficient supply to match existing and projected needs. To this end, we have examined the best practices and characterizations that have supported the current state-of-the-art driving preclinical and clinical applications. Identifying the challenges that delimit activities to supplement the donor corneal pool derived from acellular scaffolds allowed us to hypothesize a model for keratoprosthesis applications derived from livestock combining 3D printing and decellularization.

Nano-Indentation to Determine Mechanical Properties of Intraocular Lenses: Evaluating Penetration Depth, Material Stiffness, and Elastic Moduli

INTRODUCTION

Intraocular lenses (IOL) should remain in the eye for life after implantation into the capsular bag during cataract surgery. The material must meet various requirements. It is crucial that the material has the best biocompatibility, and it should be flexible and soft for best possible implantation process but also sufficiently stable and stiff for good centering in the eye and posterior capsule opacification prevention.

METHODS

In this laboratory experiment, we used nano-indentation for the mechanical assessment of three hydrophobic acrylic (A, B, C), three hydrophilic acrylic (D, E, F), and one silicone (G) intraocular lens. We wanted to determine whether some react more sensitively to touching/handling than others. The indentation elastic modulus and the creep were obtained from the force displacement curve. For measuring penetration depth and testing of possible damage to the intraocular lenses, the samples were measured at room temperature. A 200-µm-diameter ruby spherical tipped indenter was used for all the tests. Indentations were made to three different maximum loads, namely 5 mN (milli Newton), 15 mN, and 30 mN and repeated three times.

RESULTS

The lowest penetration depth (12 µm) was observed with IOL B. However, IOL A, D, and F showed similar low penetration depths (20, 18, and 23 µm, respectively). Lenses C and E showed slightly higher penetration depths of 36 and 39 µm, respectively. The silicone lens (G) showed the greatest penetration depth of 54.6 µm at a maximum load of 5 mN. With higher maximal loads (15 and 30 mN) the penetration depth increased significantly. Lens C, however, showed the same results at both 15 and 30 mN with no increase of penetration depth. This seems to fit well with the material and manufacturing process of the lens (lathe-cut). During the holding time of 30 s at constant force all six acrylic lenses showed a significant increase of the creep (CIT 21-43%). Lens G showed the smallest creep with 14%. The mean indentation modulus (EIT) values ranged from 1 to 37 MPa. IOL B had the largest EIT of 37 MPa, which could be caused by the low water content.

CONCLUSION

It was found that results correlate very well with the water content of the material in the first place. The manufacturing process (molded versus lathe-cut) seems to play another important role. Since all included acrylic lenses are very similar, it was not surprising that the measured differences are marginal. Even though hydrophobic materials with lower water content showed higher relative stiffness, penetration and defects can also occur with these. The surgeon and scrub nurse should always be aware that macroscopic changes are difficult to detect but that defects could theoretically lead to clinical effects. The principle of not touching the center of the IOL optic at any time should be taken seriously.