Lens refilling with injectable silicone in rabbit eyes

Polymeric Materials for Eye Surface and Intraocular Applications

Ocular applications of polymeric materials have been widely investigated for medical diagnostics, treatment, and vision improvement. The human eye is a vital organ that connects us to the outside world so when the eye is injured, infected, or impaired, it needs immediate medical treatment to maintain clear vision and quality of life. Moreover, several essential parts of the eye lose their functions upon aging, causing diminished vision. Modern polymer science and polymeric materials offer various alternatives, such as corneal and scleral implants, artificial ocular lenses, and vitreous substitutes, to replace the damaged parts of the eye. In addition to the use of polymers for medical treatment, polymeric contact lenses can provide not only vision correction, but they can also be used as wearable electronics. In this Review, we highlight the evolution of polymeric materials for specific ocular applications such as intraocular lenses and current state-of-the-art polymeric systems with unique properties for contact lens, corneal, scleral, and vitreous body applications. We organize this Review paper by following the path of light as it travels through the eye. Starting from the outside of the eye (contact lenses), we move onto the eye's surface (cornea and sclera) and conclude with intraocular applications (intraocular lens and vitreous body) of mostly synthetic polymers and several biopolymers. Initially, we briefly describe the anatomy and physiology of the eye as a reminder of the eye parts and their functions. The rest of the Review provides an overview of recent advancements in next-generation contact lenses and contact lens sensors, corneal and scleral implants, solid and injectable intraocular lenses, and artificial vitreous body. Current limitations for future improvements are also briefly discussed.

Advances in the Study of Lens Refilling

The ultimate goal of cataract surgery is to restore the accommodation while restoring distance visual acuity. Different kinds of accommodative intraocular lens (IOLs) and surgical techniques have been suggested to apply during the surgery, but they showed poor postoperative accommodation. It is possible to achieve this goal by refilling the lens with an injectable polymer. We present a summary of the existing materials, methods, results, and some obstacles in clinical application that remain of lens refilling for restoration of accommodation. Two main problems have restricted the clinical application of this technique. One was the formation of postoperative secondary capsule opacification and the other was the different accommodative power after surgery.

Prevention of capsule opacification after accommodating lens refilling: pilot study of strategies evaluated in a monkey model

PURPOSE

To test 2 strategies to prevent capsule opacification after accommodating lens refilling in a rhesus monkey model.

SETTING

Animal laboratory and laboratory of European university medical centers.

DESIGN

Experimental study.

METHODS

Six rhesus monkeys had refilling of the lens capsular bag. In the first strategy, before it was filled with a silicone polymer, the capsular bag was treated with noncommercial sodium hyaluronate 1.0% containing cytotoxic substances. In the second strategy, the capsular bag was filled with clinically used sodium hyaluronate 1.0% (Healon) after treatment with actinomycin-D. Slitlamp inspection was performed during a follow-up of 40 to 50 weeks. After enucleation, magnetic resonance images were obtained and confocal fluorescence imaging was performed.

RESULTS

Using the first strategy, capsule opacification developed in all eyes. Using the second strategy, 1 monkey did not develop capsule opacification after a 9-month follow-up. In a second monkey, the lens capsule remained clear for 3 months, after which the hyaluronate refill material was exchanged with a silicone polymer and capsule opacification developed. Combining these results with those in a previous study, the difference in opacification between silicone and sodium hyaluronate as refilling materials was statistically significant (P<.01).

CONCLUSIONS

That no capsular bag fibrosis occurred in the presence of hyaluronate suggests that the properties of hyaluronate are the reason that remaining lens epithelial cells do not develop into fibrotic cells. The choice of a suitable lens-refilling material prevents the development of capsule opacification.

FINANCIAL DISCLOSURE

Mr. Terwee was an employee of Abbott Medical Optics B.V. during the study period. No other author has a financial or proprietary interest in any material or method mentioned.

Carbazole-grafted silicone hydrogel with a high refractive index for intraocular lens

The refractive index (RI) is an important parameter for intraocular lens biomaterials.

Fast in situ enzymatic gelation of PPO-PEO block copolymer for injectable intraocular lens in vivo

Foldable intraocular lenses (IOLs) have been utilized to substitute natural lens of cataract patients. In this study, we developed a fast, in situ gelable hydrogel requiring no toxic agent as an injectable IOL material. A 4-armed PPO/PEO-phenol conjugate by a non-degradable linker was synthesized to form a hydrogel in situ by horseradish peroxidase. The gelation time and modulus could be controlled, ranging from 20 s to 2 min and from 1 to 43 kPa. The adhesion of human lens epithelial cells on the hydrogel was significantly reduced compared to that on commercial IOLs. The hydrogels were injected into the rabbit eyes to evaluate the in vivo biocompatibility for 8 weeks. Corneal endothelial cell loss and central corneal thickness were comparable with the common IOL implantation procedure. Histologically, the cornea and retina showed the intact structure. The change of refraction after application of pilocarpine was +0.42 D preoperatively and +0.83 D postoperatively, which may indicate the maintenance of accommodation amplitude.

Advances in lens implant technology

Cataract surgery is one of the oldest and the most frequent outpatient clinic operations in medicine performed worldwide. The clouded human crystalline lens is replaced by an artificial intraocular lens implanted into the capsular bag. During the last six decades, cataract surgery has undergone rapid development from a traumatic, manual surgical procedure with implantation of a simple lens to a minimally invasive intervention increasingly assisted by high technology and a broad variety of implants customized for each patient’s individual requirements. This review discusses the major advances in this field and focuses on the main challenge remaining – the treatment of presbyopia. The demand for correction of presbyopia is increasing, reflecting the global growth of the ageing population. Pearls and pitfalls of currently applied methods to correct presbyopia and different approaches under investigation, both in lens implant technology and in surgical technology, are discussed.

High refractive index polysiloxane as injectable, in situ curable accommodating intraocular lens

Functionalised siloxane macromonomers, with properties designed for application as an injectable, in situ curable accommodating intraocular lens (A-IOL), were prepared via re-equilibration of a phenyl group-containing polysiloxane of very high molecular weight with octamethylcyclotetrasiloxane (D₄) and 2,4,6,8-tetra(n-propyl-3-methacrylate)-2,4,6,8-tetramethyl-cyclotetrasiloxane (D₄(AM)) in toluene using trifluoromethanesulfonic acid as a catalyst. Hexaethyldisiloxane was used as an end group to control the molecular weight of the polymer. The generated polymers had a consistency suitable for injection into the empty lens capsule. The polymers contained a low ratio of polymerisable groups so that, in the presence of a photo-initiator, they could be cured on demand in situ within 5 min under irradiation of blue light to form an intraocular lens within the lens capsule. All resulting polysiloxane soft gels had a low elastic modulus and thus should be able to restore accommodation. The pre-cure viscosity and post-cure modulus of the generated polysiloxanes were controlled by the end group and D₄(AM) concentrations respectively in the re-equilibration reactions. The refractive index could be precisely controlled by adjusting the aromatic ratio in the polymer to suit such application as an artificial lens. Lens stretching experiments with both human and non-human primate cadaver lenses of different ages refilled with polysiloxane polymers provided a significant increase in amplitude of accommodation (up to 4 D more than that of the respective natural lens). Both in vitro cytotoxicity study using L929 cell lines and in vivo biocompatibility study in rabbit models demonstrated the non-cytotoxicity and ocular biocompatibility of the polymer.

Functionalised polysiloxanes as injectable, in situ curable accommodating intraocular lenses

The aged eye's ability to change focus (accommodation) may be restored by replacing the hardened natural lens with a soft gel. Functionalised polysiloxane macromonomers, designed for application as an injectable, in situ curable accommodating intraocular lens (A-IOL), were prepared via a two-step synthesis. Prepolymers were synthesised via ring opening polymerisation (ROP) of octamethylcyclotetrasiloxane (D(4)) and 2,4,6,8-tetramethylcyclotetrasiloxane (D(4)(H)) in toluene using trifluoromethanesulfonic acid (TfOH) as catalyst. Hexaethyldisiloxane (HEDS) was used as the end group to control the molecular weight of the prepolymers, which were then converted to macromonomers by hydrosilylation of the SiH groups with allyl methacrylate (AM) to introduce polymerisable groups. The resulting macromonomers had an injectable consistency and thus, were able to be injected into and refill the empty lens capsular bag. The macromonomers also contained a low ratio of polymerisable groups so that they may be cured on demand, in situ, under irradiation of blue light, in the presence of a photo-initiator, to form a soft polysiloxane gel (an intraocular lens) in the eye. The pre-cure viscosity and post-cure modulus of the polysiloxanes, which are crucial factors for an injectable, in situ curable A-IOL application, were controlled by adjusting the end group and D(4)(H) concentrations, respectively, in the ROP. The macromonomers were fully cured within 5 min under light irradiation, as shown by the rapid change in modulus monitored by photo-rheology. Ex vivo primate lens stretching experiments on an Ex Vivo Accommodation Simulator (EVAS) showed that the polysiloxane gel refilled lenses achieved over 60% of the accommodation amplitude of the natural lens. An in vivo biocompatibility study in rabbits using the lens refilling (Phaco-Ersatz) procedure demonstrated that the soft gels had good biocompatibility with the ocular tissue. The polysiloxane macromonomers meet the targeted optical and mechanical properties of a young natural crystalline lens and show promise as candidate materials for use as injectable, in situ curable A-IOLs for lens refilling procedures.

Engineering the crystalline lens with a biodegradable or non-degradable scaffold

Both a biodegradable hyaluronic acid (HA) and a nondegradable polymeric gel were evaluated as scaffolds for tissue engineering the lens in Dutch Belt pigmented and New Zealand white rabbits. Following removal of the crystalline lens through a 2 mm capsulorhexis, a collagen patch or a silicone plug was placed in the capsule bag to seal the capsulotomy. In Part I, a cross-linked HA or cohesive solution of HA was injected into the capsule bag. In Part II, a synthetic polymer (SP) was injected into the capsular bag of one eye and HA followed by SP (HA/SP) was injected into the capsule bag of the opposite eye. At 3 months focal Nd:YAG laser photocoagulation was performed in an attempt to remove some retained HA gel in one eye. Overall the regenerated lenses of the HA gel groups were spherical with excellent cortical structure and clarity and a spherical nucleus of condensed HA gel. In the one eye treated with focal photocoagulation, partial clearing of the retained HA gel was noted. In the SP and HA/SP eyes, lens regrowth around the polymer was generally clear in the anterior and peripheral capsule bag and more opacified posterior to the polymeric scaffold. In summary, naturally regenerating lens tissue was directed to grow in a more normal, regular pattern by providing a biodegradable hyaluronic acid scaffold or a nondegradable polymeric optical scaffold.

Evaluation of the performance of accommodating IOLs using a paraxial optics analysis

PURPOSE

We employed an analytical approach to evaluate the key parameters for the potential design optimisation of accommodating intra-ocular lenses (AIOL) and to use these parameters to predict their accommodative performance.

METHODS

Paraxial thin-lens equations to predict the accommodative performances of single-element (1E) and two-element (2E) AIOLs were developed. 2E-AIOLs with either mobile front or back lens elements were analysed as well as 1E-AIOL for their accommodative performance. A paraxial model including key ocular components (corneal surfaces, pupil and retina) as well as AIOL was used to evaluate the key control parameters and optimal design configurations. A range of variants of the model, representing varying powers of front and back optical elements and with either front or back optical element mobile was tested.

RESULTS

Optimal accommodative performance of 2E-AIOL is governed by the power combinations of its optical elements; design variants with higher positive front element power produced greater accommodative efficacy, while mobility of the front element contributed more to the accommodative performance than the back element. The performance of 1E-AIOL is primarily governed by the power of the AIOL; the higher the AIOL power, the better the accommodative performance.

CONCLUSIONS

From an accommodative performance standpoint, the optimal design of 2E-AIOL should comprise a high plus power front element. Considering the maximum potential amounts of element translation available clinically, 2E-AIOLs are predicted to offer higher accommodative performance compared to 1E-AIOL.

Restoration of accommodation: surgical options for correction of presbyopia

Accommodation is a dioptric change in the power of the eye to see clearly at near. Ciliary muscle contraction causes a release in zonular tension at the lens equator, which permits the elastic capsule to mould the young lens into an accommodated form. Presbyopia, the gradual age-related loss of accommodation, occurs primarily through a gradual age-related stiffening of the lens. While there are many possible options for relieving the symptoms of presbyopia, only relatively recently has consideration been given to surgical restoration of accommodation to the presbyopic eye. To understand how this might be achieved, it is necessary to understand the accommodative anatomy, the mechanism of accommodation and the causes of presbyopia. A variety of different kinds of surgical procedures has been considered for restoring accommodation to the presbyopic eye, including surgical expansion of the sclera, using femtosecond lasers to treat the lens or with so-called accommodative intraocular lenses (IOLs). Evidence suggests that scleral expansion cannot and does not restore accommodation. Laser treatments of the lens are in their early infancy. Development and testing of accommodative IOLs are proliferating. They are designed to produce a myopic refractive change in the eye in response to ciliary muscle contraction either through a movement of an optic or through a change in surface curvature. Three general design principles are being considered. These are single optic IOLs that rely on a forward shift of the optic, dual optic IOLs that rely on an increased separation between the two optics, or IOLs that permit a change in surface curvature to produce an increase in optical power in response to ciliary muscle contraction. Several of these different IOLs are available and being used clinically, while many are still in research and development.

Capsular bag refilling using a new accommodating intraocular lens

PURPOSE

To describe a capsular bag refilling procedure using an accommodating intraocular lens (IOL).

SETTING

Jinshikai Medical Foundation Nishi Eye Hospital, Osaka, Japan.

METHODS

A disk-shaped anterior foldable silicone accommodating IOL that serves as an optical device and as a mechanical device to prevent leakage of the injected silicone polymers was developed. The IOL optic is 6.0 mm and the overall diameter, 9.0 mm. After a 3.5 to 4.0 mm continuous curvilinear capsulorhexis (PCCC) is created, phacoemulsification and aspiration are performed in the usual manner. Then, a posteriorly placed accommodating IOL with sharp edges is implanted in the capsular bag to prevent posterior capsule opacification (PCO) and leakage of the injected silicone polymer. A PCCC is an option at this point. Then, an anterior accommodating IOL is piggybacked over the existing IOL and silicone polymers are injected between the 2 IOLs.

RESULTS

Experiments in numerous pig cadaver eyes and in 10 rabbit eyes showed minimal to no silicone leakage. In cases in which a PCCC was not created, 2 eyes had no PCO and 3 showed slight to moderate PCO. None of the 5 eyes with a PCCC had no PCO 5 to 8 weeks after surgery within the PCCC.

CONCLUSION

The procedure in rabbit eyes overcame 2 problems of lens-refilling techniques: leakage of the injectable silicone polymer and capsule opacification.

Accommodating intraocular lenses: a critical review of present and future concepts

BACKGROUND

Significant efforts have been made to develop lens implants or refilling procedures that restore accommodation. Even with monofocal implants, apparent or pseudoaccommodation may provide the patient with substantial though varying spectacle independence. True pseudophakic accommodation with a change of overall refractive power of the eye may be induced either by an anterior shift or a change in curvature of the lens optic.

MATERIALS AND METHODS

Passive-shift lenses were designed to move forward under ciliary muscle contraction. This is the only accommodative lens type currently marketed (43E/S by Morcher; 1CU by HumanOptics; AT-45 by Eyeonics). The working principle relies on various hypothetical assumptions regarding the mechanism of natural accommodation. Dual-optic lenses were designed to increase the dioptric impact of optic shift. They consist of a mobile front optic and a stationary rear optic which are interconnected with spring-type haptics. With active-shift lens systems the driving force is provided by repulsing mini-magnets. Lens refilling procedures replace the lens content by an elastic material and provide accommodation by an increase of surface curvature.

RESULTS

Findings with passive-shift lenses have been contradictory. While uncorrected reading vision results were initially reported to be favorable with the 1CU, and excellent with the AT-45 lens, distant-corrected near vision did not exceed that with standard monofocal lenses in later studies. Mean axial shift from laser interferometric measurements under stimulation with pilocarpine showed a moderate anterior shift with the 1CU, while the AT-45 paradoxically exhibited a small posterior shift. With the 1CU, the shift-induced accommodative effect was calculated to be less than +0.5 D in most cases, while +1 D was achieved in a single case only. Ranges and standard deviations were very large in relation to the mean values. Under physiological near-point stimulation, however, no shift was seen at all. Prevention of capsule fibrosis by extensive capsule polishing did not enhance the functional performance. Dual optic lenses are under clinical investigation and are reported to provide a significant amount of accommodation. However, possible long-term formation of interlenticular opacifications remains to be excluded. Regarding magnet-driven active-shift lens systems, initial clinical experience has been promising. Prevention of fibrotic capsular contraction is crucial, and it has been effectively counteracted with a special capsular tension ring, or lens fixation technique, together with capsule polishing. Lens refilling has been extensively studied in the laboratory and in primates. Though it offers great potential for fully restoring accommodation, a variety of problems must be solved, such as achieving emmetropia in the relaxed state, adequate response to ciliary muscle contraction, satisfying image quality over the entire range of accommodation and sustained functioning. The key problem, however, is again after-cataract prevention.

CONCLUSIONS

As opposed to psychophysical evaluation techniques, laser interferometry measures what shift lenses are designed to provide: axial shift on accommodative effort. While under pilocarpine some movement was recorded, no movement at all was found under near-point stimulation with any of the lenses currently marketed. In contrast, magnetic-driven active-shift lens systems carry the potential of sufficiently topping up apparent accommodation to provide for clinically useful accommodation while using conventional lens designs with proven after-cataract performance. Dual optic implants significantly increase the impact of axial optic shift. The main potential problem, however, is delayed formation of interlenticular regenerates. Lens refilling procedures offer the potential of fully restoring accommodation due to the great impact of increase in surface curvature on refractive lens power. However, various problems remain to be solved before clinical use can be envisaged, above all, again, after-cataract prevention. The concept of passive single-optic shift lenses has failed. Concomitant poor capsular bag performance makes these lenses an unacceptable trade-off. Magnet-assisted systems potentially combine clinically useful accommodation with satisfactory after-cataract performance. Dual optic lenses theoretically offer substantial accommodative potential but may allow for interlenticular after-cataract formation. Lens refilling procedures have the greatest potential for fully restoring natural accommodation, but will again require years of extensive laboratory and animal investigations before they may function in the human eye.

Dynamic performance of accommodating intraocular lenses in a negative feedback control system: a simulation-based study

A dynamic model of ocular accommodation is used to simulate the stability and dynamic performance of accommodating intraocular lenses (A-IOLs) that replace the hardened natural ocular lens that is unable to change focus. Accommodation simulations of an older eye with A-IOL materials having biomechanical properties of a younger eye illustrate overshoots and oscillations resulting from decreased visco-elasticity of the A-IOL. Stable dynamics of an A-IOL are restored by adaptation of phasic and tonic neural-control properties of accommodation. Simulations indicate that neural control must be recalibrated to avoid unstable dynamic accommodation with A-IOLs. An interactive web-model of A-IOL illustrating these properties is available at http://schorlab.berkeley.edu.

Predicting the performance of accommodating intraocular lenses using ray tracing

PURPOSE

To predict and compare the amount of accommodation achievable by pseudophakic accommodating intraocular lenses (IOLs) using optical ray-tracing analysis.

SETTING

Computational laboratory.

METHODS

Two-element IOLs (2E-IOL, with mobile front or back optical elements) were compared with single-element IOLs (1E-IOL). Modeling using computer-assisted ray tracing of both IOL types assumed lens elements were equiconvex/equiconcave. The 4 possible combinations of configurations representing a wide range of varying positive and negative power (up to +40 diopters [D]) of front and back optical elements were evaluated.

RESULTS

The 1E-IOLs offered limited amplitude of accommodation with axial shift (approximately 1.2 D/mm). For 2E-IOLs, configurations with high positive-power front elements returned the best amplitude of accommodation (up to approximately 3.0 D/mm when the front element power was +40 D).

CONCLUSIONS

Considering the maximum potential amounts of axial shifts available, 1E-IOLs were predicted to provide 1.0 D of accommodation or less and 2E-IOLs were predicted to provide up to 3.0 D to 4.0 D depending on design configuration and amount of axial shift achievable. Potential issues relating to accommodative aniseikonia and spherical aberration have been identified.

A light adjustable lens with injectable optics

PURPOSE OF REVIEW

Technology exists today that could permit refractive precision unheard of at the present time plus the correction of higher-order aberrations and restoration of accommodation in presbyopic adults.

RECENT FINDINGS

With the light adjustable lens, after surgery, the shape of the lens can be customized to treat spherical, cylindrical and other higher-order aberrations. The posterior surface of the lens can be adjusted to create both refractive multifocality and diffractive bifocality. It can be made out of a variety of materials, some of which can be injected into the capsule, filling it, thus replicating the original shape of a crystalline lens. While the current technique of bag filling does permit the less viscous materials to leak out of the bag this is a solvable problem. For example, a disc can fill an ordinary-sized capsulorrhexis opening, allowing removal of the cataract using standard techniques and filling behind this disc. Also the material, once injected, could be polymerized. Posterior capsule opacification is also potentially solvable with devices that completely destroy lens epithelial cells or through a polymerization process of the new lens material in which the reaction destroys the capsular cells and actually binds to the capsule.

SUMMARY

It is apparent that light adjustable lenses plus injectable technology, and multifocality can produce precise refractive correction and, hopefully, the type of accommodative range that we take for granted when we are young. Combining these technologies with a lens material that behaves like a crystalline lens of a 25 year old could precisely return near and distance vision to older adults.

Microincisional cataract surgery and Thinoptx rollable intraocular lens implantation

BACKGROUND

Microincisional cataract surgery is a safe procedure with a very short learning period for an experienced cataract surgeon and rollable ultrathin intraocular lenses eliminate the need for enlargement of corneal incision. The purpose of the study was to evaluate the safety and efficacy of cataract surgery through a corneal microincision and implantation of rollable ultrathin intraocular lenses. The setting was Dokuz Eylul University Medical Faculty, Ophthalmology Department, Izmir, Turkey and SSK Okmeydani Hospital, Ophthalmology Clinic, Istanbul, Turkey.

PATIENTS AND METHODS

Ninety eyes in 85 patients were operated on through clear corneal microincisions with sleeveless phacoemulsification and rollable intraocular lenses were implanted. Forty-six of the patients were men and 39 were women between the ages of 27 and 83, with a mean of 51 years. Two eyes had atrophic senile macular degeneration, 4 eyes had nonspecific retinal pigment epithelial changes with chorioretinal atrophy, and 4 patients had diabetes mellitus without retinopathy. Three eyes had posterior capsular opacifications of unknown etiology. Two eyes had primary open angle glaucoma (PAAG) with cup to disc ratios of about 0.5. Three eyes had dense nuclear sclerosis of grade 4 with very low visibility of retinal structures. Other patients had no ocular or systemic pathology other than nuclear/corticonuclear cataract of grade 2-3. Uncorrected and best spectacle-corrected distance and near visual acuities, keratometric values, and refractive status were noted preoperatively and 1 week, 1 month, and 6 months postoperatively. Statistical analysis of keratometric changes between preoperative and postoperative findings was performed using the paired samples t test.

RESULTS

At 6 months postoperatively, 1 patient had a best spectacle-corrected visual acuity (BSCVA) of 0.2, the patient with atrophic senile macular degeneration. The rest of the eyes achieved a BSCVA of 0.63 or better. At 6 months postoperatively, 55 (61.11%) eyes had uncorrected visual acuities (UCVA) equal to or better than 0.8 and 83 (92.22%) eyes had BSCVA equal to or better than 0.8 according to the Snellen chart. The mean postoperative corneal astigmatisms at 1 week, 1 month, and 6 months were 0.69+/-0.43 D, 0.66+/-0.46 D and 0.65+/-0.48 D respectively. Statistical analysis revealed a significant change in corneal astigmatisms at the 1st week visit (p<0.05), but not at the 1st and 6th month visits (p>0.05) compared with preoperative findings.

CONCLUSION

Based on the limited data in the literature and in this study, it is not possible to make concrete decisions about the benefits and disadvantages of the ThinOptx IOL for longer durations. Intraoperatively, this IOL apparently eliminates the need for enlargement of the corneal incision during implantation. However, the statistical insignificance of induced astigmatisms after microincisions and classical phacoincisions should also be taken into consideration. We conclude that ThinOptx IOL is a pioneering intraocular lens implant that will contribute to the exciting future of cataract refractive surgical procedures. However, both clinical and laboratory investigations are needed to clearly describe the long-term effectiveness of this new rollable IOL.

Fellow eye comparison between the 1CU accommodative intraocular lens and the Acrysof MA30 monofocal intraocular lens

PURPOSE

To examine the near visual clinical performance of an accommodative intraocular lens (IOL) when compared with a standard monofocal IOL in a fellow eye comparison.

DESIGN

Prospective, randomized fellow eye comparison.

METHODS

Thirty patients (60 eyes) with bilateral cataracts but otherwise normal eyes were recruited from a single university hospital cataract waiting list. Patients were randomized to receive either the 1CU accommodative IOL in their first eye or the Acrysof MA30 monofocal IOL. The alternative lens was then implanted in the second eye 4 to 6 weeks later. At all follow-up visits, a full assessment was made of distance, near and reading visual performance, and accommodative amplitude.

RESULTS

Data are available for all patients at 6 months and 20 patients at 1 year. At 6 months, no difference was found in distance-corrected visual acuity between the two IOLs. Of the 1CU eyes, nine patients (30%) could read J6 or better at a reading speed of 80 words/min or better. In these nine patients, the mean difference in the amplitude of accommodation between the two eyes was 0.71 diopters.

CONCLUSIONS

No measurable variable distinguished eyes that developed functional reading vision from those that did not. The accommodative IOL appears to produce improved near vision in some eyes, but it does not work in all eyes, and in eyes where there is apparent accommodation, there is a discrepancy between subjective reading performance and the modest measured increase of accommodative amplitude.

Biocompatibility of poloxamer hydrogel as an injectable intraocular lens: a pilot study

PURPOSE

To induce irreversible gelation of poloxamer, a thermosensitive polymer hydrogel, by using a photoinitiator and ultraviolet (UV) irradiation and to verify the biocompatibility and use of poloxamer as an injectable intraocular lens (IOL) material.

SETTING

Department of Ophthalmology, Seoul National University College of Medicine, Seoul Artificial Eye Center, Clinical Research Institute, Seoul National University Hospital, Seoul, Korea.

METHODS

In 10 rabbits, endocapsular phacoemulsification was performed and a poloxamer-photoinitiator mixture was injected into the capsular bag through a small capsulorhexis site. In 1 eye, the capsulorhexis site was closed with a small plug and the entire eye was irradiated with UV light for 5 minutes. Postoperatively, poloxamer transparency and effect on the conjunctiva, cornea, iris, vitreous, and retina were observed.

RESULTS

A mixture comprising 25% poloxamer and 0.01% photoinitiator produced a poloxamer that remained transparent in the lens capsule for up to 6 months. No inflammatory response or toxicity was observed in the conjunctiva, cornea, iris, vitreous, or retina.

CONCLUSION

Poloxamer is a potentially suitable material for an injectable IOL. Further study is needed.

In vitro and in vivo study of lens refilling with poloxamer hydrogel

AIM

To evaluate the compatibility of poloxamer hydrogel as a material for an injectable intraocular lens, in vivo and in vitro.

METHODS

The appropriate concentration of poloxamer hydrogel was determined for injection by examining the transparency and gelling temperature of this material, assessing the lens capsule refilling technique, and studying the postoperative findings in a rabbit model.

RESULTS

Poloxamer hydrogel showed excellent transparency and 25% was identified as an appropriate concentration for the lens refilling material. The authors developed a technique for injecting the material in vivo and obtained excellent short term results.

CONCLUSIONS

Poloxamer hydrogel was identified as an appropriate material for direct lens refilling, and the developed injection technique produced excellent short term results.

Laser cataract surgery: technique and clinical results

PURPOSE

To study the effectiveness of an erbium:YAG (Er:YAG) laser in removing nuclei of various densities.

SETTING

University clinic.

METHODS

This nonrandomized prospective clinical study included 147 consecutive cataractous eyes: Group 1 (n = 71) had conventional ultrasound, and Group 2 (n = 76) had surgery with the Er:YAG laser. The 2 groups were further classified by cataract density. Patients were examined 6 months postoperatively to evaluate surgical time, intraocular pressure (IOP), pachymetry, endothelial cell loss, and visual acuity.

RESULTS

With ultrasound cataract surgery, there were no significant changes in IOP compared with the preoperative measurements. Laser treatment of 3+ and 4+ cataracts resulted in IOP increases of 12.6% and 18.2%, respectively, compared with 1+ and 2+ cataracts (P<.001). Slight endothelial cell losses occurred in all cases. With ultrasound, the mean decrease was 2.8%, and with laser surgery, the results were similar except for a significant decrease of 13.4% with 4+ cataracts. There was a correlation between pachymetry and surgical time when the trauma related to surgical time and hydrodynamic flow in the anterior chamber was assessed. With ultrasound, the visual acuity was similar with all types of cataract; with the laser, similar normal values were seen with 1+ and 2+ cataracts but decreased values were seen with 3+ cataracts and lower values with 4+ cataracts-0.43 compared to 0.84 best corrected visual acuity with same-density cataracts treated with ultrasound (P<.0005). Patients with 4+ cataracts treated with the laser developed more complications than those treated with ultrasound.

CONCLUSIONS

The Er:YAG laser was as effective and reliable as ultrasound in removing soft and medium-density cataracts. With dense cataracts, the surgical length produced more trauma and complications during laser treatment than during ultrasound treatment.

Hydrophilic polymeric acylphospine oxide photoinitiators/crosslinkers for in vivo blue-light photopolymerization

Three vinyl-functionalized phosphine oxide photoinitiating monomers have been synthesized: 4-vinylbenzoyldiphenylphosphine oxide (VBPO), 2,6-dimethyl-4-vinylbenzoyldiphenylphosphine oxide (DMVBPO), and 2,4,6-trimethylbenzoylphenyl-4-vinylphenylphosphine oxide (TMBVPO). VBPO was copolymerized with vinylpyrrolidone or vinyl acetate (PPI-1a) and dimethylacrylamide (PPI-1b). DMVBPO and TMBVPO were both copolymerized with dimethylacrylamide (PPI-2 and PPI-3, respectively). The choice of vinylphosphine oxide and comonomer(s) had a significant influence on the properties of the resulting PPI. PPI-1a was not stable in solution in 2-hydroxyethyl methacrylate (HEMA), whereas the VBPO-dimethylacrylamide (DMA) copolymer (PPI-1b) was stable in HEMA but not stable in aqueous solutions. PPI-2 was both soluble and stable in water up to 22 months. PPI-1a was as effective as trimethylbenzoyldiphenylphosphine oxide (TPO, BASF Lucirin). PPI-2 was more effective in the polymerization of HEMA/water mixtures than PPI-3. PPI-2 and PPI-3 acted as self-cross-linking species, resulting in the formation of hydrogels; PPI 3 was more effective in this. PPI-2 was very effective in forming hydrogels based on poly(ethylene glycol) diacrylate.

Injectable intraocular lens materials based upon hydrogels

The possibilities to develop an injectable hydrogel lens were investigated. Aqueous solutions of reactive polymers in combination with a water-soluble blue light photoinitiator were transformed into hydrogels by irradiation with blue light. Poly(ethylene glycol) diacrylates (PEGDA) with low molecular weights and an acrylate modified copolymer of N-vinylpyrrolidone and vinyl alcohol with a high molecular weight were used as reactive polymers. A copolymer of (4-vinyl-2,6-dimethylbenzoyl)diphenylphosphine oxide and dimethylacrylamide was used as a water-soluble blue light photoinitiator. PEGDA showed high reactivity and the hydrogels were more transparent than the natural lens. The mass loss and the additional swelling of the hydrogel were 1.0 and 4.0%, respectively. The refractive index of these hydrogels was 1.40, lower than that of natural lens. The viscosity of the solutions before cross-linking was too low for injection into the capsular bag. Hydrogels based upon the copolymer had a transmission comparable to a 25-year-old natural lens. The materials showed no mass loss and the additional swelling after curing was less than 1%. The refractive index was comparable to that of the natural lens (1.42). The viscosity of the polymer solutions was sufficient for injection into the capsular bag without leakage.

Noninvasive Raman spectroscopic identification of intraocular lens material in the living human eye

PURPOSE

To develop a safe noninvasive technique for identifying the material of intraocular lenses (IOLs) implanted in patients.

SETTING

Center for Biomedical Engineering and the Department of Ophthalmology and Visual Sciences, University of Texas Medical Branch, Galveston, Texas, USA.

METHODS

Raman spectroscopy was used to noninvasively identify the type of IOL implanted after previous cataract surgery in 9 eyes of 6 patients who were legally blind as a result of eye disease. Three IOLs were characterized: poly(methyl methacrylate) (PMMA) (n = 5), acrylic (n = 3), and silicone (n = 1). Confocal Raman spectroscopy was used with a laser power of 95 microW and exposure time of 1 second.

RESULTS

Distinct spectral peaks associated with each type of IOL were obtained. These included spectra peaks at 2840 cm(-1), 2946 cm(-1), and 3000 cm(-1) for PMMA; 2917 cm(-1), 2939 cm(-1), and 3055 cm(-1) for acrylic; and 2900 cm(-1), 2961 cm(-1), and 3048 cm(-1) for silicone. The procedure was well accepted by patients, and there were no complications.

CONCLUSIONS

The specific Raman spectra of the IOLs allowed for noninvasive determination of IOL material with the use of a safe light dose and an exposure time of 1 second.

Laser cataract surgery : A prospective clinical evaluation of 1000 consecutive laser cataract procedures using the Dodick photolysis Nd:YAG system

BACKGROUND

To evaluate the safety and efficacy associated with the clinical use of a Q-switched neodymium:yttrium-aluminum-garnet (ND:YAG) laser for cataract removal.

DESIGN

Multicenter, prospective, noncomparative case series.

PARTICIPANTS/INTERVENTION

A total of 1000 consecutive eyes underwent cataract extraction with the photolysis Q-switched ND:YAG laser at 12 international clinical sites.

MAIN OUTCOME MEASURES

Visual acuity improvement; total energy used; mean operative time for cataract removal; complications, both intraoperative and postoperative; with a minimum follow-up of 3 months.

RESULTS

The mean values were visual acuity improvement from 20/70.2 to 20/24.4. Mean intraocular energy used was 5.65 J per case. Mean operative photolysis time among the surgeons was for up to +1 nuclear sclerosis, 2.15 minutes; up to +2 nuclear sclerosis, 4.8 minutes; and for up to +3 nuclear sclerosis, 9.8 minutes. Three cases were completed by intraocular lens implantation through the original sub-2-mm incision, using a prefolded, by dehydration, acrylic intraocular lens. Minor complications were encountered in 18 cases.

CONCLUSIONS

These data suggest this photolysis laser technology may be a safe and effective alternative for cataract extraction in human eyes. By use of small clear cornea incisions, the ability to perform cataract extraction and intraocular lens implantation with incisions less than 2 mm has been shown for the first time.

Dodick photolysis for cataract surgery: early experience with the Q-switched neodymium: YAG laser in 100 consecutive patients

OBJECTIVE

To evaluate the safety and efficacy of a Q-switched neodymium:YAG (Nd:YAG) laser for removal of the human cataract.

DESIGN

A multicenter, prospective, noncomparative study.

PARTICIPANTS

A total of 100 consecutive eyes undergoing cataract extraction with the Dodick Photolysis, Q-switched Nd:YAG laser.

MAIN OUTCOME MEASURE

Corneal endothelial cell loss, visual acuity improvement, intraocular pressure change, total intraocular energy used, and intraoperative and postoperative complications.

RESULTS

The mean values were postoperative visual acuity improvement from 20/46.5 (0.43) to 20/26.6 (0.75), decrease in endothelial cell count of 177 cells/mm2 (7.55%), and intraocular energy used of 6.7 J. Minor complications were encountered in three cases.

CONCLUSIONS

These data suggest that Dodick Photolysis may be a safe and effective new technology for cataract removal in human eyes. It appears to offer low intraocular energy and heat release, a clear-cornea incision less than 1.5 mm in size, and safe operation within the capsular bag.

Refractive cataract surgery

Today, cataract surgeons can control postoperative refraction after cataract removal with improved intraocular-lens calculation formulas and minimal invasive surgery. However, a physiologically healthy status of the human lens (transparency, accommodation) cannot yet be regained completely postoperatively. Refractional outcome should be planned by the surgeon according to the patient's requirements. The preoperative planning also should include consideration of the intraocular-lens material needed.