Effect of expandable full-size intraocular lenses on lens centration and capsule opacification in rabbits

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

Intraocular lenses (IOLs) are commonly implanted after surgical removal of a cataractous lens. A variety of IOL materials are currently available, including collamer, hydrophobic acrylic, hydrophilic acrylic, PHEMA copolymer, polymethylmethacrylate (PMMA), and silicone. High-quality polymers with distinct physical and optical properties for IOL manufacturing and in line with the highest quality standards on the market have evolved to encompass medical needs. Each of them and their packaging show unique advantages and disadvantages. Here, we highlight the evolution of polymeric materials and mainly the current state of the art of the unique properties of some polymeric systems used for IOL design, identifying current limitations for future improvements. We investigate the characteristics of the next generation of IOL materials, which must satisfy biocompatibility requirements and have tuneable refractive index to create patient-specific eye power, preventing formation of posterior capsular opacification.

Histological comparison of in vitro and in vivo development of peripheral posterior capsule opacification in human donor tissue

In order to study the mechanisms involved in the development of posterior capsule opacification (PCO) we compared in vivo developed PCO with PCO formed in tissue culture with focus on the periphery of the lens capsule to evaluate lens regeneration potential. We studied three human tissue groups: Cultured lens capsules after mock cataract surgery (n = 6, 30 days), lens capsules from donors that had previously undergone cataract surgery (IOL capsules) (n = 12) and intact lenses (n = 6). All samples were stained with Vimentin, alpha Smooth Muscle Actin, Picro Sirius Red (for collagen) and Paired box protein (Pax6). We found that cultured capsules and less developed IOL capsules consisted mainly of monolayers of mesenchymal cells, while more developed IOL capsules, contained lens epithelial cells (LECs), globular cells and lens fiber cells. Many IOL capsule samples expressed collagen I and III in areas where cells were in contact with the IOL. Pax6 had a similar dispersed distribution in less developed IOL capsules and cultured capsules, while more developed IOL capsules and intact lenses, concentrated Pax6 in LECs at the equatorial lens bow. The similarities between cultured capsules and less developed IOL capsules indicate that our in vitro developed PCO is comparable to early in vivo developed PCO. The similar morphology of more developed IOL capsules and intact lenses seems to indicate an attempt at lens regeneration.

Long-term prevention of capsular opacification after lens-refilling surgery in a rabbit model

Purpose

To reduce capsular opacification by a peri‐surgical treatment of the lens capsule with drugs in an in vivo rabbit model. Lens‐refilling surgery is a potential therapeutic intervention to treat patients with a cataract lens. The lens material is replaced with an injectable (bio)polymer that retains the natural mechanical and optical lens properties, therewith allowing accommodation. The occurrence of capsular opacification mediated by lens epithelial cells negatively affects accommodation and vision and should be avoided in this lens restoration approach.

Methods

An in vivo rabbit animal model was used with lens replacement with a silicone‐based gel‐like polymer and concurrent treatment of the lens epithelium with drugs. A case‐study approach was applied as both drug combinations and implantation times were varied. The following drugs were investigated for their potential to prevent capsular opacification long‐term: actinomycin D, methotrexate, paclitaxel and Tween‐20. All were administered in a hyaluronic acid vehicle. The rabbits were clinically followed for periods up to 4 years postimplantation. Eyes, corneas and lenses were analysed post‐mortem using MRI and confocal microscopy.

Results

Treatment combinations containing actinomycin D generally led to the least appearance of capsular fibrosis. The use of Tween‐20 or paclitaxel without actinomycin D resulted in much earlier and pronounced fibrotic responses. The aspect of capsular opacification was highly variable in individual animals. Application of the drugs in a hyaluronic acid vehicle appeared to be a safe method that spared the corneal endothelium.

Conclusion

The feasibility of long‐term prevention of fibrosis over a period of more than 4 years has been demonstrated in lens refilling in the rabbit model.

Accommodation amplitudes after an accommodating intraocular lens refilling procedure: in vivo update

PURPOSE

To evaluate whether a new capsular bag-refilling procedure provides some accommodation in monkey eyes and to assess the difference in accommodation with different volumes of capsular bag refilling.

SETTING

Jinshikai Medical Foundation, Nishi Eye Hospital, Osaka, Japan.

DESIGN

Experimental study.

METHODS

A central 3.0 to 4.0 mm continuous curvilinear capsulorhexis was created, after which phacoemulsification was performed in the usual manner. A new accommodating-membrane intraocular lens (IOL) for sealing the capsular opening was implanted in the capsular bag. Silicone polymers were injected beneath the IOL into the capsular bag through the delivery hole. In 3 study groups, each with 6 monkey eyes, the lens capsule was refilled with 0.080 mL of silicone polymers, corresponding to a 65% bag volume; 0.100 mL, corresponding to an 80% bag volume; or 0.125 mL, corresponding to a 100% bag volume. To calculate the accommodation amplitudes achieved, automated refractometry was performed before and 1 hour after topical pilocarpine 4.0% application preoperatively and 4 weeks postoperatively.

RESULTS

The refilling technique was successful without polymer leakage in all monkeys. Four weeks after surgery, the mean accommodation amplitudes were 2.56 diopters (D) ± 0.74 (SD), 2.42 ± 1.00 D, and 2.71 ± 0.63 D, respectively, in the 3 study groups.

CONCLUSIONS

The technique provided some accommodation in young monkey eyes. Leakage of the injectable silicone polymers and anterior capsule opacification in the visual axis were avoided. The results suggest that the capsular bag-refilling procedure warrants further study for possible clinical application.

FINANCIAL DISCLOSURE

All authors have a proprietary interest in the accommodating membrane IOL mentioned in the article.

[Lens refilling]

Cataract surgery has developed into a very safe and highly reproducible procedure but the ultimate goal to also restore physiological accommodation has not yet been achieved. A variety of accommodative intraocular lenses (IOLs) and surgical techniques have been suggested to cure presbyopia but all showed only poor accommodative effects by objective measurements. Complete lens refilling with flexible polymers might be an interesting alternative. Recent investigations on accommodation and presbyopia have given support to the lens refilling method. After development of suitable surgical techniques and filling materials only secondary cataract formation and the unsolved intraoperative control of refraction restrict the clinical use of this technique.

Effect of blue staining of expandable hydrophilic intraocular lenses on contrast sensitivity and glare vision

PURPOSE

To evaluate the effect of trypan blue staining of expandable hydrophilic acrylic intraocular lenses (IOLs) on contrast sensitivity and glare.

SETTING

Department of Ophthalmology, Federal University, and Oculistas Associados, Rio de Janeiro, Brazil.

METHODS

Phacoemulsification with expandable hydrophilic IOL implantation was performed in 19 eyes. Group 1 (stained group) consisted of 12 eyes with the IOL unintentionally stained by trypan blue 0.1% solution during surgery; Group 2 (unstained group) consisted of 7 eyes with IOLs that were not stained because trypan blue was not used during surgery. The eyes were examined postoperatively for Snellen best corrected visual acuity (BCVA), contrast sensitivity BCVA, and glare vision. The examiners were masked to whether the IOL was stained by trypan blue. Inclusion criteria included a BCVA of 20/30 or better 1 month postoperatively. Patients who had other ocular pathology or previous ocular surgery were excluded from the study.

RESULTS

The mean postoperative BCVA was 20/24 in the stained group and 20/23 in the unstained group (P =.73). The mean contrast sensitivity visual acuity was 20/31 in the stained group and 20/26 in unstained group (P =.10). The mean glare visual acuity was 20/75 and 20/33, respectively (P =.03).

CONCLUSIONS

Patients with expandable hydrophilic acrylic IOLs stained with trypan blue performed significantly worse on a glare vision test than patients whose IOLs were not stained. Cataract surgeons should avoid using trypan blue with this IOL type.

Permanent blue discoloration of a hydrogel intraocular lens by intraoperative trypan blue

A 79-year-old white man had cataract surgery in the right eye with implantation of an Acqua intraocular lens (IOL) (Mediphacos). Trypan blue 0.1% was used during surgery to stain the anterior capsule and enhance the contrast during capsulorhexis. Seven days after surgery, the patient presented with "dark and double" vision (monocular diplopia). The IOL was decentered superiorly and appeared dark blue. The lens was explanted 2 months after surgery and sent for gross and microscopic analyses in a dry state and after hydration. The same analyses were performed on 2 unused lenses of the same design that had been immersed in diluted trypan blue solutions (0.01% and 0.001%). On the explanted lens, the dark blue staining was denser in the optic, especially in its periphery. The blue discoloration could not be removed after 24 hours of lens immersion in a balanced salt solution at 37 degrees C. Permanent staining of the unused lenses was also obtained after immersion in the trypan blue solutions.

Modulating fibroblast cell proliferation with functionalized poly(methyl methacrylate) based copolymers: chemical composition and monomer distribution effect

Poly(methyl methacrylate)-based terpolymers bearing sulfonate and carboxylate groups have been synthesized by radical copolymerization leading to polymers with random distributions of ionic monomer units. Fibroblast cells were seeded on terpolymers of various molar compositions of ionic groups. Kinetics of the cell proliferation were examined and systematically compared to the nonfunctionalized control polymer, poly(methyl methacrylate). Modulation of cell proliferation was observed on 15% ionic monomer content copolymers of various compositions (R = COO(-)/(COO(-) + SO(3)(-)) and varies from 0 to 1). The inhibition percentage of cell proliferation calculated for each polymer by comparison to the cell proliferation on the control was plotted against R and gave a maximum value for R close to 0.55. Copolymers with ionic group contents higher or lower than 15% exhibit inhibition percentages fitting with those previously observed for the same R values, showing that the hydrophilic properties are not sufficient to explain the modulation effect of this material toward cells. Moreover, for each polymer tested, cells, even if inhibited in growth, were shown to be viable, indicating that the synthesized terpolymers exhibit cytostatic properties excluding any cytotoxic effect. Such polymers may be used for the fabrication of biocompatible intraocular lenses and prevent secondary cataract.

Experimental studies of capsular equator rings of soft latex

PURPOSE

To determine the efficacy of wide equatorial rings of various materials in reducing posterior capsule opacification (PCO) and maintaining the circular contour of the capsular equator in a rabbit model.

SETTING

Laboratory for Intraocular Microsurgery and Implants, Goldschleger Eye Research Institute, Tel-Aviv University, Sheba Medical Center, Tel-Hashomer, Israel.

METHODS

Closed rings made of poly(methyl methacrylate), Teflon(R), polyurethane, and latex were introduced into the capsular bags of rabbit eyes after removal of the lens material. The soft latex rings were deemed the only practical rings for atraumatic implantation through a small incision. Latex rings of 2 dimensions with rectangular edges were implanted in 8 rabbits. One eye served as a control after lens removal and no ring implantation. The eyes were followed for up to 5 months and then evaluated by light microscopy.

RESULTS

Posterior capsule opacification was minimal or absent in all animals implanted with the latex rings. Mild to moderate inflammatory reaction was noted in most eyes. It was caused by the ring material or secondary to long-standing pressure on the ciliary tissue. The rings also maintained well the circular contour of the capsular bags.

CONCLUSIONS

Equatorial rings of soft latex with sharp rectangular edges were effective in minimizing PCO and maintaining the shape of the capsule after lens removal in rabbits. Soft rings made of a biocompatible material may be effective in humans.

Posterior capsule opacification

Posterior capsule opacification (PCO) is the most common complication following primary cataract surgery. Advances in intraocular lens (IOL) designs that have reduced the amount of PCO following surgery have been made. The understanding of how the IOL design effects PCO has also advanced. Lenses that provide a mechanical barrier between it and the posterior lens capsule seem to inhibit PCO to a greater degree. Intracapsular rings are now being explored to test and enhance this barrier effect. Major advances in the elimination of lens epithelial cells at the time of surgery especially by pharmacologic means have also been made. An immunotoxin specific for human lens epithelial cells shows promise and is under latter phase clinical development.