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

Development Pattern of Medical Device Technology and Regulatory Evolution of Cataract Treatment

To prevent regulation from becoming an obstacle to healthcare technological innovation, regulation should evolve as new healthcare technologies are developed. Although regulation is closely related to healthcare technology development, there are few studies that view healthcare technological advances from the multi-layered perspective of papers, patents, and clinical research and link this with regulatory evolution. Therefore, this study tried to develop a new method from a multi-layer perspective and draw regulatory implications based on it. This study applied this method to intraocular lens (IOLs) for cataract treatment and detected four major healthcare technologies and two recent healthcare technologies. Moreover, it discussed how current regulations evaluate these technologies. The findings provide implications for healthcare technological advances and the evolutionary direction of regulation through the example of IOLs for cataract treatment. This study contributes to the development of theoretical methods for co-evolution with regulations based on healthcare technology innovation.

The lens epithelium as a major determinant in the development, maintenance, and regeneration of the crystalline lens

The crystalline lens is a transparent and refractive biconvex structure formed by lens epithelial cells (LECs) and lens fibers. Lens opacity, also known as cataracts, is the leading cause of blindness in the world. LECs are the principal cells of lens throughout human life, exhibiting different physiological properties and functions. During the embryonic stage, LECs proliferate and differentiate into lens fibers, which form the crystalline lens. Genetics and environment are vital factors that influence normal lens development. During maturation, LECs help maintain lens homeostasis through material transport, synthesis and metabolism as well as mitosis and proliferation. If disturbed, this will result in loss of lens transparency. After cataract surgery, the repair potential of LECs is activated and the structure and transparency of the regenerative tissue depends on postoperative microenvironment. This review summarizes recent research advances on the role of LECs in lens development, homeostasis, and regeneration, with a particular focus on the role of cholesterol synthesis (eg., lanosterol synthase) in lens development and homeostasis maintenance, and how the regenerative potential of LECs can be harnessed to develop surgical strategies and improve the outcomes of cataract surgery (Fig. 1). These new insights suggest that LECs are a major determinant of the physiological and pathological state of the lens. Further studies on their molecular biology will offer possibility to explore new approaches for cataract prevention and treatment.

Long-Term Evaluation of Visual Outcomes and Patient Satisfaction after Binocular Implantation of a Bioanalogic Lens

Purpose

Long-term evaluation of the visual refractive outcomes and the quality of life after implantation of the WIOL-CF (Medicem, Czech Republic) in both eyes.

Design

retrospective, nonrandomized noncomparative case series.

Methods

50 eyes of 25 patients, including 11 women (44%) and 14 men (56%). The age range of the patients was 38 to 77 years (mean age 55.48 ± 10.97 years). All patients underwent bilateral implantation of the WIOL-CF. Exclusion criteria were previous ocular surgeries except for cataract surgery and refractive lens exchange, irregular corneal astigmatism of >1.0 diopter, and ocular pathologies or corneal abnormalities. Postoperative examinations were performed at 14 days and 3, 6, 12 months of surgery; the last follow-up was between 24 and 36 months after the procedure. All exams included manifest refraction, monocular uncorrected visual acuity (UCVA) and distance-corrected visual acuity (DCVA) in 5 m (Snellen), monocular uncorrected visual acuity in 70 cm and 40 cm (Jeager) and binocular UCVA, DCVA in 5 m, 70 cm, and 40 cm, binocular contrast sensitivity (CS) under photopic conditions, binocular defocus curves, high-order aberrations, quality-of-vision VF-14 questionnaire, and spectacle independence.

Results

Significant improvement in monocular visual acuity at all distances was demonstrated; the mean postoperative spherical equivalent was 0.32 ± 0.45D. The postoperative means of binocular distance UCVA and BCVA were also improved (p < .001) and so were the mean uncorrected intermediate VA (2.053 ± 1.268) and near uncorrected VA (2.737 ± 1.447). There was a significant improvement in contrast sensitivity at all spatial frequencies and higher-order aberration, compared to preoperative results.

Conclusions

The evaluation of a WIOL-CF showed good distance, intermediate, and near visual acuity. Contrast sensitivity increased after surgery in all spatial frequencies. Patient satisfaction was high despite some optical phenomena. The rate of postoperative spectacle independence also turned out high. Financial Disclosure. No author has a financial or proprietary interest in any material or method mentioned.

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.

Lens-based surgical correction of presbyopia. Where are we in 2020?

INTRODUCTION

Presbyopia is the progressive and irreversible loss of accommodation due to aging. It is one of the main causes of loss of quality of life in people from 45 years of age, due to the, often novel, dependence on spectacles. The eagerness to correct it by ophthalmologists impulsed by the desire of millions of people who suffer from it, has become one of the main drivers for the development of intraocular lens (IOL) technology over the last twenty years.

MATERIAL AND METHODS

This review briefly presents the different alternatives that have allowed us to improve the crystalline lens surgical approach of presbyopia; from monofocal lenses and monovision technique, accommodative, refractive, and diffractive multifocal lenses, and finally the most recent extended depth of focus/field lenses known as EDOFs.

RESULTS

Each IOL has its advantages, limitations and disadvantages. Furthermore, there is no single lens that suits the needs of all patients.

CONCLUSIONS

It is necessary to know the variety of lenses available, and to have an in-depth understanding of their optical properties, as well as the impact that these will have later on their clinical performance and on the visual quality of the patients. This should help us to select the best alternative for each of them.

Optimized multielement accommodative intraocular lens with a four-freeform-surface Alvarez lens and a separate aspheric lens

This paper proposes an accommodative intraocular lens (IOL), which consists of a two-element Alvarez lens and an aspheric lens for changing focal power and refractive power, respectively. The four-freeform-surface Alvarez lens is optimized for a multiple field of view; further, the aspheric lens also corrects the aberrations induced by the corneal asphericity of the human eye over the whole range of accommodation. A simulation using optical design software demonstrates its excellent performance in that the values of the modulation transfer function at 100 cycles/mm all reach ∼0.4 with a ±5° field of view for 3 and 5 mm pupils.

Advances and challenges of intraocular lens design [Invited]

Phacoemulsification technique with intraocular lens implantation has been a common treatment for cataract patients. With rising demand among the public, new technologies for lens design have emerged to minimize intraocular aberrations, improving visual quality to the largest extent. This paper systematically reviews the development of materials applied in lens manufacturing, the different categories of intraocular lenses, and respective design principles. The advantages and potential drawbacks of intraocular lenses are illustrated in the paper, and prospective research to improve the design are presented in the end.

Clinical application of accommodating intraocular lens

The present review describes recent advances in application of accommodating intraocular lenses (AIOLs). Standard monofocal intraocular lenses (MIOLs) only correct distance vision, while AIOLs are designed to allow both good distance vision and near vision, which is achieved through the contraction and relaxation of ciliary muscles by providing transformation of the axial movement or curvature of the lens. Thus, AIOLs may be a better choice for those patients who demand a higher level of visual performance. Since techniques to analyze the performance of AIOLs have not been standardized, and there is a variety of both subjective and objective methods, it is hard to measure the performance of these intraocular lenses. By evaluating advantages and disadvantages of various AIOLs, and introducing techniques for measurement the performance postoperative, this paper can provide some relative information on choosing the type of AIOLs in the clinic.

Correction of presbyopia: An integrated update for the practical surgeon

Presbyopia results from loss or insufficiency of the eye's accommodative ability, and clinically manifests as the inability to focus near objects on the retina. It is one of the most common causes of visual impairment worldwide especially in adults of productive or working age. Various means of compensating for the loss of accommodative ability have been devised from optical tools such as spectacles and contact lenses, to topical medications and to surgical procedures. A comprehensive search on journal articles about topical and surgical correction of presbyopia was undertaken. The various techniques for presbyopia correction, as enumerated in these articles, are discussed in this paper with the addition of our personal experience and perspective on the future of these techniques.

Achromatic doublet intraocular lens for full aberration correction

A doublet intraocular lens optimized for both chromatic and monochromatic aberration correction in pseudophakic eyes is presented. Ray-tracing techniques were applied to design the lens in white light within a chromatic eye model. Combinations of two materials, already commonly used in intraocular lenses, as acrylic and silicone, were used. Iterative optimization algorithms were employed to correct for longitudinal chromatic aberration, spherical aberration and off-axis aberrations within 10 degrees of visual field. The performance of this lens was compared with a standard single-material aspheric intraocular lens. Near full aberration correction was achieved with the doublet intraocular lens. The modulation transfer function and Strehl ratio were superior for the doublet lens. Through-focus calculations were also conducted showing better optical quality for the doublet. Real higher-order aberrations from normal eyes were incorporated in the model to evaluate the effect on the doublet intraocular lens performance. Results showed that the doublet lens preserved its benefits under realistic conditions. This doublet intraocular lens should provide patients with a better quality of vision after it is further developed in terms of manufacturing and surgical limitations.

Near vision examination in presbyopia patients: Do we need good homologated near vision charts?

Presbyopia correction is mainly concerned with the goal of regaining an uncorrected reading performance. Since historic reading charts do not provide a unique standard that is applicable for the analysis of clinical and scientific reading performance, new standardized reading charts have been developed, in order to provide reading performance analyses analogous to modern single-optotype distance acuity measurements: the Bailey-Lovie Word Reading Chart, the Colenbrander English Continuous Text Near Vision Cards, the MNREAD Charts, and the RADNER Reading Charts. The last three are also meant to measure reading speed, thus allowing detailed analysis of the reading capabilities of the patient’s functional vision. Furthermore, these reading charts can be declared homologated, based on the standards that were published for reading charts by the Visual Function Committee of the International Council of Ophthalmology (ICO) in 1988. Many research studies have shown that by analyzing the reading performance with homologated reading charts, valuable insight into the reading performance of patients suffering from various diseases can be obtained. These reading charts have also been successfully used in presbyopia research. It therefore seems evident that homologated, standardized reading charts facilitate not only research concerning functional vision in many fields of ophthalmology but also international communication about near visual performance. Homologated reading charts are available in almost all languages and have become a valuable tool in analyzing reading performance. We argue in this review that homologated reading charts are clearly a necessity for presbyopia research.

The Predictability of Preoperative Pilocarpine-Induced Lens Shift on the Outcomes of Accommodating Intraocular Lenses Implanted in Senile Cataract Patients

Purpose. To evaluate the predictability of lens shift induced by pilocarpine (LSPilo) on the outcomes of accommodating intraocular lens (Acc-IOL) implantation. Methods. Twenty-four eyes of 24 senile cataract patients who underwent phacoemulsification and Acc-IOL implantation were enrolled. LSPilo was evaluated with anterior segment optical coherence tomography (AS-OCT). At 3 months postoperatively, the best corrected distance visual acuities (BCDVA), distance-corrected near visual acuities (DCNVA), and subjective and objective accommodations were measured. IOL shifts under accommodation stimulus (IOLSAcc) were evaluated with AS-OCT. Results. The mean LSPilo was 112.29 ± 30.72 µm. LSPilo was not associated with any preoperative parameters. The mean IOLSAcc was 130.46 ± 42.71 µm. The mean subjective and objective accommodation were 1.54 ± 0.39 D and 1.27 ± 0.41 D, respectively. The mean postoperative BCDVA and DCNVA (log MAR value) were 0.22 ± 0.11 and 0.24 ± 0.12, respectively. LSPilo positively correlated with IOLSAcc (r = 0.541; P = 0.006), subjective accommodation (r = 0.412; P = 0.022), and objective accommodation (r = 0.466; P = 0.045), respectively. Conclusion. LSPilo is an independent preoperative parameter associated with the postoperative Acc-IOL mobility and pseudophakic accommodation. It may offer valuable information for ophthalmologists in determining the suitable candidates for Acc-IOL implantation.

Axial movement of the dual-optic accommodating intraocular lens for the correction of the presbyopia: optical performance and clinical outcomes

Presbyopia occurs in the aging eye due to changes in the ciliary muscle, zonular fibers, crystalline lens, and an increased lens sclerosis. As a consequence, the capacity of accommodation decreases, which hampers to focus near objects. With the aim of restoring near vision, different devices that produce multiple focuses have been developed and introduced. However, these devices are still unable to restore accommodation. In order to achieve that goal, dual-optic accommodating Intraocular Lenses have been designed, whose anterior optic displaces axially to increase ocular power, and focus near objects. Although dual-optic accommodating IOLs are relatively new, their outcomes are promising, as they provide large amplitudes of accommodation and a greater IOL displacement than single-optic accommodating IOLs. The outcomes show comfortable near vision, higher patients' satisfaction rates, and minimal postoperative complications like Posterior Capsular Opacification and Anterior Capsular Opacification, due to their design and material.

Physiological constraints for an intraocular inductive distance sensor

In this paper the design restrictions of an inductive sensor for an intraocular lens with focus control on the basis of a marker implanted in the ciliary muscle of the eye are discussed in the framework of anatomical and physiological influences and constraints: limitations on the marker size, influences of tissue conduction and effects of off-axis implantation of the marker with respect to the coil.

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

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

Clinical performance of a new aspheric dual-optic accommodating intraocular lens

Purpose

To describe the clinical performance of a new dual-optic intraocular lens (IOL) with an enhanced optic profile designed to mimic natural accommodation.

Patients and methods

Prospective multicenter clinical study with the new dual-optic aspheric accommodating IOL (Synchrony Vu) in 74 patients (148 eyes) undergoing cataract surgery. Refractive target was emmetropia. Examinations at 1 month and 6 months included subjective refractions; visual acuities at near, intermediate, and far; mesopic contrast sensitivity with and without glare; safety data; and subjective survey on dysphotopsia (halos and glare).

Results

Clinical data at 6 months showed 89% of the eyes within ±1.0 D spherical equivalent refraction. Mean binocular uncorrected and distance-corrected visual acuity was 20/20 at far (0.00±0.11 logMAR and −0.06±0.08 logMAR, respectively), 20/20 at intermediate (0.01±0.13 logMAR and −0.01±0.10 logMAR, respectively), and 20/25 at near (0.10±0.14 logMAR and 0.14±0.15 logMAR, respectively). Mesopic contrast sensitivity was within normal limits. Seventy-eight percent of the patients had no spectacles and 70% had no dysphotopsia. One eye had IOL repositioning within 1 month of surgery.

Conclusion

The new aspheric Synchrony Vu accommodating IOL provided good visual performance at a range of distances without affecting quality of vision and with minimal safety considerations.

[Femtosecond laser in cataract surgery. A critical appraisal]

BACKGROUND

The use of femtosecond lasers (FSL) is increasingly spreading in cataract surgery. Potential advantages over standard manual cataract surgery are the superior precision of corneal incisions and capsular openings as well as the reduction of ultrasound energy for lens nucleus work-up. Exact positioning and dimensioning of the anterior capsular opening should help reduce decentration and tilt of the intraocular lens (IOL) optics and thus achieve better target refraction. Together with the possibility to correct low-grade corneal astigmatism by precise arcuate incision, FSL technology is expected to convert cataract surgery from a purely curative into a refractive procedure.

METHODS

Apart from own experiences this review article critically analyses the pertinent literature published so far as well as congress presentations and personal reports of other FSL surgeons. The advantages and disadvantages are scrutinized with regard to their impact on the surgical and refractive results and compared with those experienced by the authors with manual cataract surgery over several decades. Economic and healthcare political aspects are also addressed.

RESULTS

The use of FSL surgery improves the precision and reproducibility of corneal incisions and the capsular opening and reduces the amount of ultrasound energy required for lens nucleus work-up. However, the clinical benefits must be put into perspective due to the subsequent surgical manipulation of the incisions (during lens emulsification, aspiration and IOL injection), the lacking possibility to visualize the crystalline lens equator as the reference for correct capsulotomy centration and the relativity of ultrasound energy consumption on the corneal endothelial trauma. This is of particular relevance against the background of the significantly higher costs. Conversely, tears of the anterior capsule edge which, apart from interfering with correct IOL positioning, may entail serious complications presently occur more frequently with all FSL instruments. From the economic and healthcare political viewpoint, thought should be given to the possible acquisition of the cataract surgical business by the industry or investors, as cataract surgery is a high-volume standardized procedure with enormous future potential. This could fundamentally change our currently decentralized and individualized structures and subsequently the steam of patient and make surgeons largely dependent or superfluous.

Current management of presbyopia

Presbyopia is a physiologic inevitability that causes gradual loss of accommodation during the fifth decade of life. The correction of presbyopia and the restoration of accommodation are considered the final frontier of refractive surgery. Different approaches on the cornea, the crystalline lens and the sclera are being pursued to achieve surgical correction of this disability. There are however, a number of limitations and considerations that have prevented widespread acceptance of surgical correction for presbyopia. The quality of vision, optical and visual distortions, regression of effect, complications such as corneal ectasia and haze, anisometropia after monovision correction, impaired distance vision and the invasive nature of the currently techniques have limited the utilization of presbyopia surgery. The purpose of this paper is to provide an update of current procedures available for presbyopia correction and their limitations.

Accommodative intraocular lens versus standard monofocal intraocular lens implantation in cataract surgery

BACKGROUND

Following cataract surgery and intraocular lens (IOL) implantation, loss of accommodation or postoperative presbyopia occurs and remains a challenge. Standard monofocal IOLs correct only distance vision; patients require spectacles for near vision. Accommodative IOLs have been designed to overcome loss of accommodation after cataract surgery.

OBJECTIVES

To define (a) the extent to which accommodative IOLs improve unaided near visual function, in comparison with monofocal IOLs; (b) the extent of compromise to unaided distance visual acuity; c) whether a higher rate of additional complications is associated the use of accommodative IOLs.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2013, Issue 9), Ovid MEDLINE, Ovid MEDLINE in-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily Update, Ovid OLDMEDLINE (January 1946 to October 2013), EMBASE (January 1980 to October 2013), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to October 2013), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrial.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 10 October 2013.

SELECTION CRITERIA

We include randomised controlled trials (RCTs) which compared implantation of accommodative IOLs to implantation of monofocal IOLs in cataract surgery.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results, assessed risk of bias and extracted data. All included trials used the 1CU accommodative IOL (HumanOptics, Erlangen, Germany) for their intervention group. One trial had an additional arm with the AT-45 Crystalens accommodative IOL (Eyeonics Vision). We performed a separate analysis comparing 1CU and AT-45 IOL.

MAIN RESULTS

We included four RCTs, including 229 participants (256 eyes), conducted in Germany, Italy and the UK. The age range of participants was 21 to 87 years. All studies included people who had bilateral cataracts with no pre-existing ocular pathologies. We judged all studies to be at high risk of performance bias. We graded two studies with high risk of detection bias and one study with high risk of selection bias.Participants who received the accommodative IOLs achieved better distance-corrected near visual acuity (DCNVA) at six months (mean difference (MD) -3.10 Jaeger units; 95% confidence intervals (CI) -3.36 to -2.83, 2 studies, 106 people, 136 eyes, moderate quality evidence). Better DCNVA was seen in the accommodative lens group at 12 to 18 months in the three trials that reported this time point but considerable heterogeneity of effect was seen, ranging from 1.3 (95% CI 0.98 to 1.68; 20 people, 40 eyes) to 6 (95% CI 4.15 to 7.85; 51 people, 51 eyes) Jaeger units and 0.12 (95% CI 0.05 to 0.19; 40 people, binocular) logMAR improvement (low quality evidence). The relative effect of the lenses on corrected distant visual acuity (CDVA) was less certain. At six months there was a standardised mean difference of -0.04 standard deviations (95% CI -0.37 to 0.30, 2 studies, 106 people, 136 eyes, low quality evidence). At long-term follow-up there was heterogeneity of effect with 18-month data in two studies showing that CDVA was better in the monofocal group (MD 0.12 logMAR; 95% CI 0.07 to 0.16, 2 studies, 70 people,100 eyes) and one study which reported data at 12 months finding similar CDVA in the two groups (-0.02 logMAR units, 95% CI -0.06 to 0.02, 51 people) (low quality evidence).The relative effect of the lenses on reading speed and spectacle independence was uncertain, The average reading speed was 11.6 words per minute more in the accommodative lens group but the 95% confidence intervals ranged from 12.2 words less to 35.4 words more (1 study, 40 people, low quality evidence). People with accommodative lenses were more likely to be spectacle-independent but the estimate was very uncertain (risk ratio (RR) 8.18; 95% CI 0.47 to 142.62, 1 study, 40 people, very low quality evidence).More cases of posterior capsule opacification (PCO) were seen in accommodative lenses but the effect of the lenses on PCO was uncertain (Peto odds ratio (OR) 2.12; 95% CI 0.45 to 10.02, 91 people, 2 studies, low quality evidence). People in the accommodative lens group were more likely to require laser capsulotomy (Peto OR 7.96; 95% CI 2.49 to 25.45, 2 studies, 60 people, 80 eyes, low quality evidence). Glare was reported less frequently with accommodative lenses but the relative effect of the lenses on glare was uncertain (RR any glare 0.78; 95% CI 0.32 to 1.90, 1 study, 40 people, and RR moderate/severe glare 0.45; 95% CI 0.04 to 4.60, low quality evidence).

AUTHORS' CONCLUSIONS

There is moderate-quality evidence that study participants who received accommodative IOLs had a small gain in near visual acuity after six months. There is some evidence that distance visual acuity with accommodative lenses may be worse after 12 months but due to low quality of evidence and heterogeneity of effect, the evidence for this is not clear-cut. People receiving accommodative lenses had more PCO which may be associated with poorer distance vision. However, the effect of the lenses on PCO was uncertain.Further research is required to improve the understanding of how accommodative IOLs may affect near visual function, and whether they provide any durable gains. Additional trials, with longer follow-up, comparing different accommodative IOLs, multifocal IOLs and monofocal IOLs, would help map out their relative efficacy, and associated late complications. Research is needed on control over capsular fibrosis postimplantation.Risks of bias, heterogeneity of outcome measures and study designs used, and the dominance of one design of accommodative lens in existing trials (the HumanOptics 1CU) mean that these results should be interpreted with caution. They may not be applicable to other accommodative IOL designs.

Developments in the correction of presbyopia II: surgical approaches

PURPOSE

To discuss the various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances.

CONTENT

Static methods broadly adopt the same optical techniques as those used in presbyopic contact lens correction and aim to satisfy the needs of the presbyope by increasing binocular depth-of-focus, often using monovision as well as simultaneous-imagery. Dynamic methods generally attempt to make use of at least some of the still-active elements of the accommodation system. They include procedures which are supposed to modify the relative geometry of the ciliary muscle and lens, or which reduce the stiffness of the presbyopic lens either by replacing it with other natural or man-made material or by subjecting it to femtosecond laser treatment. Alternatively the natural lens may be replaced by some form of intraocular lens which changes power as a result of forces derived from the still-active ciliary muscle, zonule and capsule, or other sources.

CONCLUSIONS

At present, multifocal intraocular lenses appear to offer the most consistent and reliable surgical approach to surgical presbyopic correction. They have obvious advantages in convenience and stability over optically-similar, simultaneous-image presbyopic contact lenses but this must be balanced against their relative inflexibility in cases of patient dissatisfaction. Dynamic methods remain largely experimental. Although some approaches show promise, as yet no method has demonstrated a reliable, long-term ability to correct distance refractive error and to appropriately change ocular power in response to changes in viewing distance over the normal range of interest.

Intraocular lens based on double-liquid variable-focus lens

In this work, the crystalline lens in the Gullstrand-Le Grand human eye model is replaced by a double-liquid variable-focus lens, the structure data of which are based on theoretical analysis and experimental results. When the pseudoaphakic eye is built in Zemax, aspherical surfaces are introduced to the double-liquid variable-focus lens to reduce the axial spherical aberration existent in the system. After optimization, the zoom range of the pseudoaphakic eye greatly exceeds that of normal human eyes, and the spot size on an image plane basically reaches the normal human eye's limit of resolution.

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.

Crystalens HD intraocular lens analysis using an adaptive optics visual simulator

PURPOSE

To compare visual and optical quality of the Crystalens HD intraocular lens (IOL) with that of a monofocal IOL.

METHODS

The wavefront aberration patterns of the monocular Akreos Adapt AO IOL and the single-optic accommodating Crystalens HD IOL were measured in a model eye. The Crystalens IOL was measured in its nonaccommodative state and then, after flexing the haptic to produce 1.4 mm of movement, in its accommodative state. Using an adaptive optics system, subjects' aberrations were removed and replaced with those of pseudophakes viewing with either lens. Monocular distance visual acuity (DVA) at high (100%), medium (50%), and low (10%) contrast and contrast sensitivity (CS) were measured for both IOL optics. Near VA (NVA) and CS were measured for the Crystalens HD IOL in its accommodative state. Depth of focus around the distance and near focus was also evaluated for the Crystalens HD IOL. Modulation transfer function (MTF), point spread function (PSF), and Strehl ratio were also calculated. All measures were taken for 3- and 5-mm pupils.

RESULTS

The MTF, PSF, and Strehl ratio showed comparable values between IOLs (p > 0.05). There were no significant differences in DVA and CS between IOLs for all contrasts and pupils (p > 0.05). When spherically focused, mean DVA and NVA with the Crystalens HD IOL were ≥20/20 at 100 and 50% contrasts for both pupils. Monocular DVA, NVA, and CS were slightly better with 3- than 5-mm pupils, but without statistically significant differences. The Crystalens HD IOL showed about 0.75 and 0.50 D of depth of focus in its accommodative state and nonaccommodative state, respectively.

CONCLUSIONS

The optical and visual quality with the nonaccommodatied Crystalens HD IOL was comparable to that of a monofocal IOL. If this lens can move 1.4 mm in the eye, it will provide high-quality optics for near vision as well.

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.

Intraocular electro-optic lens with ciliary muscle controlled accommodation

In this paper a concept is proposed of an intraocular lens implant with electro-optic accommodation of a variable-focus hybrid liquid-crystal-based lens. The dioptric strength of the lens is electronically controlled by a signal that is derived from the change of inductance of a sensing coil due to a marker implanted in the nearby contracting or decontracting ciliary muscle. Analytical, numerical and experimental results are reported on the dependency of the frequency of a Colpitts oscillator circuit on the location of a nearby conductive marker. A concept is also reported on the use as an electro-optic lens of a device based on a liquid crystal in planar alignment, which is held between a flat and a curved window coated with optically transparent and electrically conductive layers.

Surgical management of presbyopia

Presbyopia, the gradual loss of accommodation that becomes clinically significant during the fifth decade of life, is a physiologic inevitability. Different technologies are being pursued to achieve surgical correction of this disability; however, a number of limitations have prevented widespread acceptance of surgical presbyopia correction, such as optical and visual distortion, induced corneal ectasia, haze, anisometropy with monovision, regression of effect, decline in uncorrected distance vision, and the inherent risks with invasive techniques, limiting the development of an ideal solution. The correction of the presbyopia and the restoration of accommodation are considered the final frontier of refractive surgery. The purpose of this paper is to provide an update about current procedures available for presbyopia correction, their advantages, and disadvantages.

Effect of primary posterior continuous curvilinear capsulorrhexis with posterior optic buttonholing on pilocarpine-induced IOL shift

PURPOSE

To assess intraocular lens (IOL) shift along the visual axis induced by ciliary muscle contraction with pilocarpine after cataract surgery and to compare primary posterior continuous curvilinear capsulorrhexis (CCC) and posterior optic buttonholing with IOLs implanted in the bag.

SETTING

Department of Ophthalmology, Medical University of Vienna, Vienna, Austria.

DESIGN

Clinical trial.

METHODS

Eyes with age-related cataract had cataract surgery with implantation of a nonaccommodating IOL (AF-1 YA-60BB). Surgery was performed with primary posterior CCC and posterior buttonholing in 1 eye (study eyes) and with conventional in-the-bag implantation in the contralateral eye (control eyes). After a minimum of 6 months postoperatively, the anterior chamber depth was assessed with partial coherence interferometry before and after application of pilocarpine 2.0% and, after a washout interval of 1 week, before and after the application of cyclopentolate 1.0%.

RESULTS

Forty eyes of 20 patients were enrolled. A slight backward shift of the IOL (+78 μm) in study eyes and in control eyes (+118 μm) was detected after pilocarpine application (both P<.05). No significant difference in IOL shift was found between study eyes and control eyes (P=.19).

CONCLUSIONS

Combined primary posterior CCC and posterior optic buttonholing did not affect IOL shift during pharmacologically stimulated ciliary muscle contraction compared with in-the-bag implanted IOLs. Capsule fibrosis diminished with primary posterior CCC but did not seem to be the only limiting factor in the accommodative IOL shift.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

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.

Objective evaluation of through-focus optical performance of presbyopia-correcting intraocular lenses using an optical bench system

PURPOSE

TO evaluate spherical aberration and through-focus optical performances of 5 presbyopia-correcting and 2 monofocal intraocular lenses (IOLs).

SETTING

Flaum Eye Institute, University of Rochester, Rochester, New York, USA.

DESIGN

Experimental study.

METHODS

Five presbyopia-correcting IOLs (Restor +4D SN6AD3, Restor +3D SN6AD1, Rezoom NXG1, Tecnis multifocal ZM900, Crystalens HD500) were tested using an optical bench system consisting of a model eye, a high-resolution Hartmann-Shack wavefront sensor, and an image-capturing device. Two monofocal IOLs (Sofport AO LI60AOV, Acrysof SN60AT) were measured for comparison. No accommodation was simulated. The spherical aberration profiles of each IOL were measured using the wavefront sensor. Through-focus performance was evaluated by calculating cross-correlation coefficients and comparing the likenesses of captured images of a resolution target and a perfect reference image.

RESULTS

With a 5.0 mm entrance pupil, the SN6AD3, SN6AD1, ZM900, NXG1, and HD500 IOLs had spherical aberration of -0.18 μm, -0.14 μm, -0.15 μm, -0.07 μm, and -0.01 μm, respectively. Distance image quality was poorer with multifocal and accommodating IOLs than with monofocal IOLs. All multifocal IOLs had effective distance and near image quality but had a loss in intermediate image quality. The HD 500 accommodating IOL had decreased distance image quality and slightly increased depth of focus compared with the monofocal IOLs because of the bispheric design.

CONCLUSIONS

The presbyopia-correcting IOLs had different optical characteristics, including spherical aberration profile and through-focus performance. An accurate understanding of the optical characteristics of individual IOLs is essential to selecting the best presbyopia-correcting IOL and thus improving cataract surgery outcomes.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

The influence of injection volume and capsular bag contraction on the refractive power of polymer refilled lenses - a finite element modelling simulation study

PURPOSE

Polymer injection into the capsular bag after phakoemulsification is an interesting and promising approach to lens surgery. Safe clinical application of this technique will require an appropriate estimate of the effect of implantation variables on the lens power. This article details the results of finite element investigations into the effects of the injected polymer volume and capsular bag contraction on the resultant lens power and accommodation amplitude.

METHODS

An axisymmetric finite element model was created from literature sources. Polymer injection and the capsular contraction were simulated, and their effect on the lens power was calculated.

RESULTS AND CONCLUSION

The simulations show that overfilling during polymer injection leads to a refractive power increase of the lens. Capsular bag contraction also results in a power increase. The calculated accommodative amplitude of the lens is minimally affected by capsular bag contraction but decreases significantly with increased capsular bag stiffness as a result of fibrosis.

Strehl ratios characterizing optical elements designed for presbyopia compensation

We present results of numerical analysis of the Strehl ratio characteristics for the light sword optical element (LSOE). For comparison there were analyzed other optical imaging elements proposed for compensation of presbyopia such as the bifocal lens, the trifocal lens, the stenopeic contact lens, and elements with extended depth of focus (EDOF), such as the logarithmic and quartic axicons. The simulations were based on a human eye's model being a simplified version of the Gullstrand model. The results obtained allow to state that the LSOE exhibits much more uniform characteristics of the Strehl ratio comparing with other known hitherto elements and therefore it could be a promising aid to compensate for the insufficient accommodation range of the human eye.

Static and dynamic accommodation measured using the WAM-5500 Autorefractor

PURPOSE

This study was undertaken to compare static and dynamic accommodation measurements using the Grand Seiko WR-5500 (WAM) in young, phakic subjects.

METHODS

Fifteen subjects, aged 20 to 28 years (23.8 ± 0.58 years; mean ± SD years) participated. Accommodation was stimulated with printed text presented at various distances. In static mode, three measurements were taken for each stimulus amplitude. In dynamic mode, 5-Hz recordings were started, and subjects alternately looked through a transparent near chart and focused on a letter chart at 6 m for 5 seconds and then focused on the near letter chart for 5 seconds for a total of 30 seconds. After smoothing the raw data, the highest three individual values recorded in each 5-s interval of focusing at near were averaged for each stimulus amplitude. Analysis of variance and Bland-Altman analysis were used to compare the static and dynamic measurements. A calibration was performed with +3.00 to -10.00 D trial lenses behind an infrared filter, in 1.00 D steps in 5 of the 15 subjects.

RESULTS

Stimulus-response graphs from static and dynamic modes were not significantly different in the lower stimulus range (<5.00 D, p = 0.93), but differed significantly for the higher stimulus amplitudes (p = 0.0027). One of the 15 subjects showed a significant difference between the static and dynamic modes. Corresponding pupil diameter could be recorded along with the accommodation responses for the subjects, and pupil diameter decreased with increasing stimulus demand. Calibration curves for static and dynamic measurements were not significantly different from the 1:1 line or from each other (p = 0.32).

CONCLUSIONS

Slight differences between the dynamically and statically recorded response amplitudes were identified. This is attributed to differences in the accommodative responses in this population and not to the instrument performance. Dynamic measurement of accommodation and pupil constriction potentially provides additional useful information on the accommodative response other than simply the response amplitude.

Objective evaluation of the changes in the crystalline lens during accommodation in young and presbyopic populations using Pentacam HR system

AIM

To quantify the changes in the lens profile with accommodation in different age groups.

METHODS

The Pentacam HR system was used to obtain the images of the anterior eye segment from 23 young and 15 presbyopic emmetropic subjects in unaccommodated (with an accommodation stimulus of 0.0D) and accommodated (with an accommodation stimulus of 5.0D for the young group and 1.0D for the presbyopic group) states. The phakic crystalline lens shape, including curvature of crystalline lens and central lens thickness (CLT), and the measurements of anterior segment length (ASL), central anterior chamber depth (CACD) were investigated. The anterior chamber volume (ACV) was also measured.

RESULTS

The reduction of CACD and ACV were significant in both groups after accommodation stimulus. From the profile of anterior eye segment, a significant decrease in anterior crystalline lens radii of curvature (-2.52mm) and a mean increase in CLT (0.222mm) and ASL (0.108mm) were found in the young group with an accommodation stimulus of 5.0D. However, no statistically significant changes of CLT, ASL, or crystalline lens radii of curvature were found in the presbyopic group.

CONCLUSION

Our data showed that the shallowing of anterior chamber during accommodation was caused by the forward bulging of the anterior lens surface, rather than by anterior shifting of lens position in either young or presbyopic subjects.

Ex vivo quantification of the time course of contractile loading of the porcine lens capsule after cataract-like surgery

Cataract surgery is an invasive procedure that replaces the quasi-spherical native lens fibers with a flat prosthetic device, which initially reduces mechanical stress within the remnant lens capsule and, ultimately, leads to contraction of the capsule about the implant. Although resultant changes in geometry have been quantified previously, little is known about the loads associated with this contraction. We present a novel experimental culture device to quantify ex vivo the time course of increases in tension within the contracting lens capsule after cataract-like surgery. Results demonstrate that contraction reaches steady state within approximately one month with a mean tension of 1.45 mN/mm and Cauchy (true) stress of 13.4 kPa. A significant increase in alpha-smooth muscle actin (alpha-SMA) was also found in post-cultured compared to fresh lens capsules, thus suggesting that transdifferentiated lens epithelial cells (LECs) modulated the contraction. Quantification of loads imparted by the contracting lens capsule is important for assessing implant/capsule interactions and implant stability in vivo. Because contraction of the capsule may be modulated in part by LECs attempting to restore their native mechanical environment, our results further suggest a possible mechanism for the long-term errant changes in capsular structure commonly observed after surgery.