Synchrony dual-optic accommodating intraocular lens

Influence of the CleaRing intraocular open capsule device on refractive predictability in cataract surgery

BACKGROUND

The marked improvement in cataract surgery and intraocular lens (IOL) quality has led to a decline in posterior capsular opacification (PCO) incidence; however, PCO remains a common complication of cataract surgery. The CleaRing intraocular capsule open device (IOCD) decreases PCO incidence. We aimed to investigate the influence of the CleaRing IOCD on refractive predictability in cataract surgery.

METHODS

We conducted this prospective pilot study at the Wolfson Medical Center, Holon, Israel. Ten eyes of patients who underwent cataract surgery and insertion of an IOL after IOCD implantation into the capsular bag were included. All patients completed 12 months of follow-up, including refraction, measurement of uncorrected (UDVA) and best-corrected distance visual acuity (CDVA), slit-lamp biomicroscopy, and ultrasound biomicroscopy.

RESULTS

All the surgeries were uneventful, with no postoperative complications. The IOL was centred in the device and bag in all cases. The mean prediction error at 1 and 12 months postoperatively was +0.28 ± 0.32 D and +0.50 ± 0.32 D, respectively. The mean UDVA was 0.17 ± 0.13 and 0.15 ± 0.11 logMAR, and the mean CDVA was 0.04 ± 0.10 and 0.04 ± 0.06 logMAR, respectively. The manifest refractive cylinders at 12 months postoperatively were compatible with corneal astigmatism.

CONCLUSIONS

Implantation of the IOCD resulted in a slight, predicted, and stable hyperopic shift with a low standard deviation. The standard deviation of the prediction error demonstrated excellent refractive accuracy and predictability using the IOCD, which was as low as 0.32 D at the 12-month follow-up.

Estimation of the full shape of the crystalline lens in-vivo from OCT images using eigenlenses

Quantifying the full 3-D shape of the human crystalline lens is important for improving intraocular lens power or sizing calculations in treatments of cataract and presbyopia. In a previous work we described a novel method for the representation of the full shape of the ex vivo crystalline lens called eigenlenses, which proved more compact and accurate than compared state-of-the art methods of crystalline lens shape quantification. Here we demonstrate the use of eigenlenses to estimate the full shape of the crystalline lens in vivo from optical coherence tomography images, where only the information visible through the pupil is available. We compare the performance of eigenlenses with previous methods of full crystalline lens shape estimation, and demonstrate an improvement in repeatability, robustness and use of computational resources. We found that eigenlenses can be used to describe efficiently the crystalline lens full shape changes with accommodation and refractive error.

Effect of age and cycloplegia on the morphology of the human crystalline lens: swept-source OCT study

PURPOSE

To evaluate the effect of age and cycloplegia on the morphology of the crystalline lens using a swept-source optical coherence tomography (SS-OCT) system.

SETTING

Hospital.

DESIGN

Prospective cross-sectional study.

METHODS

The parameters including anterior chamber depth (ACD), the radii of curvature of the anterior and posterior surface of the crystalline lens (ALR and PLR), lens thickness (LT), lens equatorial diameter (LED), and lens vault (LV) were quantified by the SS-OCT before and after cycloplegia. The paired t test was used to compare the parameters before and after cycloplegia. A multivariate linear regression model was built to analyze the association between the parameters/cycloplegia-induced changes and age, while adjusting for the effect of axial length, refractive status, and sex.

RESULTS

76 individuals (age range, 18 to 86 years) were recruited. The ALR and ACD were negatively correlated with age (P ≤ .002), and the LT, LV, and LED were positively correlated with age (P ≤ .004). In participants younger than 60 years, the ALR and ACD significantly increased, whereas the LV and LT significantly decreased after cycloplegia (all P < .001). With aging, cycloplegia-induced differences of ALR (P = .001) and ACD (P = .014) significantly decreased, and of LT (P < .001), LT (P < .001), and LV (P = .001) significantly increased.

CONCLUSIONS

The crystalline lens morphology measured by the SS-OCT revealed steepening anterior surface and increasing equatorial diameter with age. Cycloplegia caused a significant change of anterior surface morphology in participants younger than 60 years, and this effect diminished with age.

Simulating Outcomes of Cataract Surgery: Important Advances in Ophthalmology

As the human eye ages, the crystalline lens stiffens (presbyopia) and opacifies (cataract), requiring its replacement with an artificial lens [intraocular lens (IOL)]. Cataract surgery is the most frequently performed surgical procedure in the world. The increase in IOL designs has not been paralleled in practice by a sophistication in IOL selection methods, which rely on limited anatomical measurements of the eye and the surgeon's interpretation of the patient's needs and expectations. We propose that the future of IOL selection will be guided by 3D quantitative imaging of the crystalline lens to map lens opacities, anticipate IOL position, and develop fully customized eye models for ray-tracing-based IOL selection. Conversely, visual simulators (in which IOL designs are programmed in active elements) allow patients to experience prospective vision before surgery and to make more informed decisions about which IOL to choose. Quantitative imaging and optical and visual simulations of postsurgery outcomes will allow optimal treatments to be selected for a patient undergoing modern cataract surgery.

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.

Further Enhancement of Intraocular Open-Capsule Devices for Prevention of Posterior Capsule Opacification

Purpose

We improve the intraocular open-capsule devices (IOCD) for the prevention of posterior capsule opacification (PCO).

Methods

A total of 45 New Zealand rabbit eyes were divided into six similar groups after crystalline lens evacuation. Each group was implanted with a hydrophilic intraocular lens (IOL) and a hydrophilic IOCD of different designs. In the first experiment (Part A), a square design ring with and without large apertures was compared to a round design ring without apertures. In the second experiment (Part B), a square design ring with large apertures was compared to square design IOCDs with small apertures of high and low density. PCO and Soemmering's ring were evaluated clinically, by the Miyake Apple view, and histologically. The results were compared to a control group of eyes implanted with a hydrophilic IOL only.

Results

All devices showed significant prevention of PCO and Soemmering's ring compared to the control group. Part A: the square design with apertures had the lowest level of peripheral lens epithelial cells proliferation (protrusions). Part B: modifying the size and density of the apertures had no influence on those protrusions.

Conclusions

The IOCD significantly reduced the rate of PCO and its precursor, Soemmering's ring. The rings with the square edges and apertures produced the best results. The study was underpowered to determine the influence of the apertures design.

Translational Relevance

The IOCD has the potential to prevent up to 80% of the PCO cases; the most common complication after cataract surgery. The design of the ring is important for its success.

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.

Accommodating Intraocular Lenses

With an explosive increase in the worldwide prevalence of presbyopia, development of an accommodating intraocular lens (IOL) with expansive accommodative amplitude remains the holy grail in lens-based refractive surgery. A dynamic change in the dioptric power of the eye can be accomplished by various strategies alone or in combination, including changes in the position, shape, or refractive index of a single- or dual- optic IOL. This article reviews the cumulative advances in these various lens designs, along with clinical outcomes and complications of those that have been implanted. The challenges that remain in each cat-egory are also highlighted.

Prevention of postoperative capsular bag opacification using intraocular lenses and endocapsular devices maintaining an open or expanded capsular bag

Postoperative capsule opacification is a multifactorial physiological consequence of cataract surgery that remains the most common complication of this procedure. A literature review that included several intraocular lenses (IOLs) and endocapsular devices studied in our laboratory found that devices maintaining the capsular bag in an open or expanded state were associated with improved bag clarity. This observed effect likely occurs secondary to the complex interactions of myriad mechanisms, which include formation of a barrier to lens epithelial cell (LEC) migration, mechanical compression of residual LECs, mechanical stretch at the level of the capsule equator, maintenance of overall bag contour, and enhanced endocapsular circulation of aqueous humor. We review the designs of endocapsular devices and IOLs that minimize the degree of postoperative capsule opacification by preventing capsular bag collapse and discuss the underlying mechanisms that contribute to this phenomenon.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Evaluation of long-term biocompatibility and capsular bag opacification with a new silicone-polyimide plate-type intraocular lens in the rabbit model

PURPOSE

To evaluate the long-term biocompatibility and safety of the new SC9 intraocular lens (IOL) after implantation in rabbit eyes, in accordance with the requirements of the International Organization for Standardization 11979-5, Annex G:2006(E).

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Bilateral phacoemulsification was performed on 9 New Zealand white rabbits; 1 eye received the test IOL and the contralateral eye received a commercially available plate-type silicone control IOL (AA4204VL). Two rabbits were humanely killed at 2 months and the remaining at 6 months. After gross examination of the eyes from the posterior Miyake-Apple view, select IOLs were explanted and had surface staining for implant cytology. All globes were then sectioned and processed for complete histopathologic examination.

RESULTS

Overall uveal biocompatibility was similar between the test IOLs and control IOLs throughout the study. The mean posterior capsule opacification at 6 months was 0.8 ± 0.27 (SD) in the test group and 4.0 ± 0 in the control group (P = .001, t test: paired 2-sample for means). The mean posterior synechiae formation at 6 months was 1.28 ± 1.25 in the test group and 2.71 ± 0.75 in the control group (P = .01). A histopathologic examination confirmed the relative lack of capsule opacification in the study eyes compared with the control eyes and the absence of untoward inflammatory reaction or toxicity in all eyes.

CONCLUSION

The new IOL maintained an open capsular bag secondary to its design, which appeared to prevent overall capsular bag opacification and retain uveal and capsule biocompatibility.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Prediction of accommodative optical response in prepresbyopic subjects using ultrasound biomicroscopy

PURPOSE

To determine whether relatively low-resolution ultrasound biomicroscopy (UBM) can be used to predict the accommodative optical response in prepresbyopic eyes as well as in a previous study of young phakic subjects, despite lower accommodative amplitudes.

SETTING

College of Optometry, University of Houston, Houston, USA.

DESIGN

Observational cross-sectional study.

METHODS

Static accommodative optical response was measured with infrared photorefraction and an autorefractor (WR-5100K) in subjects aged 36 to 46 years. A 35 MHz UBM device (Vumax, Sonomed Escalon) was used to image the left eye, while the right eye viewed accommodative stimuli. Custom-developed Matlab image-analysis software was used to perform automated analysis of UBM images to measure the ocular biometry parameters. The accommodative optical response was predicted from biometry parameters using linear regression, 95% confidence intervals (CIs), and 95% prediction intervals.

RESULTS

The study evaluated 25 subjects. Per-diopter (D) accommodative changes in anterior chamber depth (ACD), lens thickness, anterior and posterior lens radii of curvature, and anterior segment length were similar to previous values from young subjects. The standard deviations (SDs) of accommodative optical response predicted from linear regressions for UBM-measured biometry parameters were ACD, 0.15 D; lens thickness, 0.25 D; anterior lens radii of curvature, 0.09 D; posterior lens radii of curvature, 0.37 D; and anterior segment length, 0.42 D.

CONCLUSIONS

Ultrasound biomicroscopy parameters can, on average, predict accommodative optical responses with SDs of less than 0.55 D using linear regressions and 95% CIs. Ultrasound biomicroscopy can be used to visualize and quantify accommodative biometric changes and predict accommodative optical response in prepresbyopic eyes.

Stretch-dependent changes in surface profiles of the human crystalline lens during accommodation: a finite element study

BACKGROUND

A non-linear isotropic finite element (FE) model of a 29-year-old human crystalline lens was constructed to study the effects of various geometrical parameters on lens accommodation.

METHODS

The model simulates dis-accommodation by stretching of the lens and predicts the change in surface profiles of the lens capsule, cortex and nucleus at select states of stretching/accommodation. Multiple regression analysis (MRA) is used to develop a stretch-dependent mathematical model relating the lens sagittal height to the radial position of the lens surface as a function of dis-accommodative stretch. A load analysis is performed to compare the finite element results to empirical results from lens stretcher studies. Using the predicted geometrical changes, the optical response of the whole eye during accommodation was analysed by ray-tracing.

RESULTS

Aspects of lens shape change relative to stretch were evaluated, including change in diameter, central thickness and accommodation. Maximum accommodation achieved was 10.29 D. From the multiple regression analysis, the stretch-dependent mathematical model of the lens shape related lens curvatures as a function of lens ciliary stretch well (maximum mean-square residual error 2.5 × 10(-3 ) μm, p < 0.001). The results are compared with those from in vitro studies.

CONCLUSIONS

The finite element and ray-tracing predictions are consistent with Ex Vivo Accommodation Simulator (EVAS) studies in terms of load and power change versus change in thickness. The mathematical stretch-dependent model of accommodation presented may have utility in investigating lens behaviour at states other than the relaxed or fully accommodated states.

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.

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.

Long-term uveal and capsular biocompatibility of a new accommodating intraocular lens

PURPOSE

To evaluate long-term uveal and capsular biocompatibility of a new accommodating intraocular lens (IOL).

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Bilateral phacoemulsification was performed in 14 rabbits; 1 eye received the accommodating IOL (Fluidvision) and the other received a hydrophobic acrylic control IOL. Slitlamp examinations were performed at postoperative weeks 1 to 4 and months 2, 3, 4, and 6. Six rabbits were humanely killed at 2 months and 8 rabbits at 6 months. After gross examination with the Miyake-Apple view, selected IOLs were removed for implant cytology. All globes were then sectioned and processed for histopathologic examination.

RESULTS

Uveal biocompatibility of study and control IOLs was similar in clinical and pathologic examinations up to 6 months postoperatively. In the study group, anterior capsule opacification appeared absent and posterior capsule opacification (PCO) was significantly less than in the control group. At the gross examination at 6 months, central PCO was 0.8 ± 0.5 (SD) in the study IOLs and 3.7 ± 0.4 in the control IOLs (P < .0001, 2-tailed paired t test). Histopathologic examination confirmed the relative lack of capsule opacification in study eyes compared with controls and the absence of untoward inflammatory reaction or toxicity in all eyes.

CONCLUSIONS

The accommodating IOL maintained an expanded capsular bag secondary to the large size of the haptic elements without significant contact with the anterior capsule. This appeared to prevent overall capsular bag opacification and to retain uveal and capsular biocompatibility.

Influence of intraocular lens implantation on anterior capsule contraction and posterior capsule opacification

PURPOSE

To evaluate whether and how intraocular lens (IOL) implantation influences the development of anterior capsule contraction and posterior capsule opacification (PCO).

SETTING

Department of Ophthalmology, Dokkyo Medical University, Mibu, Tochigi, Japan.

DESIGN

Experimental study.

METHODS

Phacoemulsification was performed in 8-week-old white rabbits. A hydrophobic acrylate IOL (12.5 mm) (YA-60BBR) was implanted in 1 eye and no IOL was implanted in the fellow eye. Slitlamp microscopy and anterior segment analysis were performed to evaluate anterior capsule contraction after the surgery. Four weeks postoperatively, sections of the eyes were made, and the thickness of the proliferated lens epithelial cell (LEC) layer at the posterior capsule was measured to assess the PCO. In addition, LECs from white rabbits were cultured in medium containing 50% aqueous humor or in medium containing 50% saline to determine the influence of the aqueous humor on LECs and to compare the degree of LEC proliferation.

RESULTS

Starting 2 weeks after surgery, anterior capsule contraction progressed more significantly in the IOL group than in the group without IOLs. Four weeks postoperatively, LEC thickness at the posterior capsule was significantly less in the group without IOLs than in the IOL group. In the culture study, LEC proliferation was more inhibited in the aqueous humor group than in the saline group.

CONCLUSIONS

Progression of anterior capsule contraction and PCO is less likely in aphakic eyes than in IOL-implanted eyes. The mechanism of prevention may involve aqueous humor-induced inhibition of LEC proliferation.

Aberrometry in patients implanted with accommodative intraocular lenses

PURPOSE

To evaluate the objective accommodative response, change of aberrations, and depth of focus in eyes implanted with the Crystalens accommodative intraocular lens (IOL) at different accommodative demands.

DESIGN

Prospective, observational study.

METHODS

Eleven cataract patients (22 eyes) who underwent implantation of a Crystalens accommodative IOL, and control groups of 9 normal subjects (17 eyes) and 17 pseudophakic patients (17 eyes) implanted with monofocal IOLs were evaluated. A custom-developed laser ray tracing aberrometer was used to measure the optical aberrations. The monochromatic wave aberrations were described using a sixth-order Zernike polynomial expansion. Measurements were obtained under dilated and natural viewing conditions (for accommodative efforts ranging from 0 to 2.5 diopters [D]). The accommodative response was obtained by analyzing changes in paraxial defocus (associated to changes in defocus) and by evaluating the differences in the effective defocus (associated with defocus, spherical aberrations, and pupil diameter) with the accommodative demand. Depth of focus was estimated from through-focus objective optical quality.

RESULTS

Wave aberration measurements were highly reproducible. Vertical trefoil (Z3(-3)) was the predominant higher-order aberration in the Crystalens group and significantly higher (P < .0001) than in the young group, but similar to the monofocal IOL group. The coma root mean square also was higher (P < .005) in the Crystalens group than in the young group. On average, the defocus term (Z2(0)), astigmatism, or higher-order aberrations did not change systematically with accommodative demand in Crystalens eyes. As found for paraxial defocus, the effective defocus in Crystalens eyes did not show significant differences between conditions: 0.34 ± 0.48 D (far), 0.32 ± 0.50 D (intermediate), and 0.34 ± 0.44 D (near). Depth of focus was statistically significantly higher in the Crystalens eyes than in the control groups.

CONCLUSIONS

The accommodative response of eyes implanted with the Crystalens accommodative IOLs, measured objectively using laser ray tracing aberrometry, was lower than 0.4 D in all eyes. Several subjects showed changes in astigmatism, spherical aberration, trefoil, and coma with accommodation, which must arise from geometrical and alignment changes in the lens with accommodative demand. Pseudoaccommodation from increased depth of focus may contribute to near vision functionality in Crystalens-implanted patients.

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.

Vignetting and field of view with the KAMRA corneal inlay

PURPOSE

To evaluate the effect of the KAMRA corneal inlay on the retinal image brightness in the peripheral visual field.

METHODS

A KAMRA inlay was "implanted" into a theoretical eye model in a corneal depth of 200 microns. Corneal radius was varied to a steep, normal, and flat (7.37, 7.77, and 8.17 mm) version keeping the proportion of anterior to posterior radius constant. Pupil size was varied from 2.0 to 5.0 mm. Image brightness was determined for field angles from -70° to 70° with and without KAMRA and proportion of light attenuation was recorded.

RESULTS

In our parameter space, the attenuation in brightness ranges in between 0 and 60%. The attenuation in brightness is not affected by corneal shape. For large field angles where the incident ray bundle is passing through the peripheral cornea, brightness is not affected. For combinations of small pupil sizes (2.0 and 2.5 mm) and field angles of 20-40°, up to 60% of light may be blocked with the KAMRA.

CONCLUSION

For combinations of pupil sizes and field angles, the attenuation of image brightness reaches levels up to 60%. Our theoretical findings have to be clinically validated with detailed investigation of this vignetting effect.

The journey to femtosecond laser-assisted cataract surgery: new beginnings or a false dawn?

Femtosecond laser-assisted cataract surgery (FLACS) represents a potential paradigm shift in cataract surgery, but it is not without controversy. Advocates of the technology herald FLACS as a revolution that promises superior outcomes and an improved safety profile for patients. Conversely, detractors point to the large financial costs involved and claim that similar results are achievable with conventional small-incision phacoemulsification. This review provides a balanced and comprehensive account of the development of FLACS since its inception. It explains the physiology and mechanics underlying the technology, and critically reviews the outcomes and implications of initial studies. The benefits and limitations of using femtosecond laser accuracy to create corneal incisions, anterior capsulotomy, and lens fragmentation are explored, with reference to the main platforms, which currently offer FLACS. Economic considerations are discussed, in addition to the practicalities associated with the implementation of FLACS in a healthcare setting. The influence on surgical training and skills is considered and possible future applications of the technology introduced. While in its infancy, FLACS sets out the exciting possibility of a new level of precision in cataract surgery. However, further work in the form of large scale, phase 3 randomised controlled trials are required to demonstrate whether its theoretical benefits are significant in practice and worthy of the necessary huge financial investment and system overhaul. Whether it gains widespread acceptance is likely to be influenced by a complex interplay of scientific and socio-economic factors in years to come.

Biomechanical eye model and measurement setup for investigating accommodating intraocular lenses

We present a biomechanical eye model to induce pseudophakic accommodative movement for evaluation of the focal shift of accommodative intraocular lenses. Therefore, an accommodative intraocular lens (IOL) was implanted into freshly enucleated porcine eyes. The eyes were glued into a mechanical apparatus to expand the ciliar body effectuating mechanical accommodation. An optical coherence tomographer was used to measure positional and geometrical changes of the IOL for different levels of expansion. The expansion unit allowed stretching of the globe of several millimeters. With the biomechanical eye model we were able to simulate the mechanical functionality of accommodation as well as to measure the lens vault and change in geometry. Accommodative vault could only be measured with an intact vitreous, indicating that the vitreous plays an important role for the functionality of accommodative IOLs.

Materials characterization and mechanobiology of the eye

The eye responds to a great deal of internal and external stimuli throughout its normal function. Due to this, a mechanical or chemical analysis alone is insufficient. A systematic materials characterization is needed. A mechanobiological approach is required for a full understanding of the unique properties and function of the eye. This review compiles the mechanical properties of select eye components, summarizes mechanical and chemical testing platforms, and overviews modeling approaches. Analysis is done across studies, experimental methods, and between species in order to summarize what is known about the mechanobiology of the eye. Several opportunities for future research are identified.

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.

Femtosecond laser-assisted cataract surgery with integrated optical coherence tomography

About one-third of people in the developed world will undergo cataract surgery in their lifetime. Although marked improvements in surgical technique have occurred since the development of the current approach to lens replacement in the late 1960s and early 1970s, some critical steps of the procedure can still only be executed with limited precision. Current practice requires manual formation of an opening in the anterior lens capsule, fragmentation and evacuation of the lens tissue with an ultrasound probe, and implantation of a plastic intraocular lens into the remaining capsular bag. The size, shape, and position of the anterior capsular opening (one of the most critical steps in the procedure) are controlled by freehand pulling and tearing of the capsular tissue. Here, we report a technique that improves the precision and reproducibility of cataract surgery by performing anterior capsulotomy, lens segmentation, and corneal incisions with a femtosecond laser. The placement of the cuts was determined by imaging the anterior segment of the eye with integrated optical coherence tomography. Femtosecond laser produced continuous anterior capsular incisions, which were twice as strong and more than five times as precise in size and shape than manual capsulorhexis. Lens segmentation and softening simplified its emulsification and removal, decreasing the perceived cataract hardness by two grades. Three-dimensional cutting of the cornea guided by diagnostic imaging creates multiplanar self-sealing incisions and allows exact placement of the limbal relaxing incisions, potentially increasing the safety and performance of cataract surgery.

Computational model of evolving lens capsule biomechanics following cataract-like surgery

Cataract surgery is an invasive procedure whereby lens fibers are removed through a permanent central hole, or capsulorhexis, in the surrounding lens capsule and replaced with an artificial intraocular lens (IOL). Remnant lens epithelial cells subsequently transdifferentiate to a more contractile and synthetic wound-healing phenotype, which causes significant structural and mechanical adaptations of the residual lens capsule. The goal of this study is to present a computational model capable of capturing salient features of the biomechanical evolution of the lens capsule following cataract-like surgery. The model is shown to predict marked long-term increases in thickness and stiffness of the lens capsule nearest the edge of the capsulorhexis comparable to reported measurements. Such models represent a first step toward understanding better the long-term interactions between the residual lens capsule and implanted IOL, thus initiating a new paradigm for the design of improved IOLs, including those having an accommodative feature.

Pilot study of new focus-shift accommodating intraocular lens

PURPOSE

To determine the visual and accommodative performance of the OPAL-A focus-shift accommodating intraocular lens (IOL).

SETTING

Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

METHODS

In this study comprising unilateral phacoemulsification and accommodating IOL implantation, patients were followed for 6 months. Corrected distance (CDVA) and distance-corrected near (DCNVA) visual acuities were measured. Objective amplitude of accommodation was measured with an autorefractor and subjective amplitude of accommodation, using push-up tests and defocus curves. Physiological and pilocarpine-stimulated IOL movement was measured by anterior segment optical coherence tomography.

RESULTS

The mean values at 1 month, 3 months, and 6 months, respectively, were as follows: CDVA, -0.06 +/- 0.08 (SD), -0.08 +/- 0.09, and -0.05 +/- 0.09; DCNVA, 0.31 +/- 0.15, 0.31 +/- 0.15, and 0.34 +/- 0.16; objective amplitude of accommodation, 0.36 +/- 0.38 diopters (D), 0.12 +/- 0.34 D, and 0.10 +/- 0.34 D; subjective amplitude of accommodation, 2.79 +/- 0.86 D, 2.55 +/- 0.85 D, and 2.50 +/- 0.62 D with push-up test and 0.90 +/- 0.40 D, 0.78 +/- 0.23 D, and 0.93 +/- 0.35 D with defocus curves. The maximum physiologic IOL shift at 1 month (mean 45.2 +/- 63.4 microm) occurred with a 3.0 D accommodative stimulus. At 6 months, the mean pilocarpine-stimulated forward IOL shift was 306 +/- 161 microm.

CONCLUSIONS

Objective accommodation and forward axial shift were clinically insignificant with the accommodating IOL. The near visual performance was attributed to depth of focus rather than to true pseudophakic accommodation.

Anterior chamber depth measurements in eyes with an accommodating intraocular lens: agreement between partial coherence interferometry and optical coherence tomography

PURPOSE

To determine agreement between partial coherence interferometry (PCI) and anterior segment optical coherence tomography (AS-OCT) measurements of anterior chamber depth (ACD) and axial intraocular lens (IOL) movement in eyes with an accommodating IOL.

SETTING

Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

METHODS

In this prospective pilot study of cataract patients, the central ACD was measured by PCI (ACMaster) and AS-OCT (Visante) 6 months after unilateral OPAL-A accommodating IOL implantation. Measurements were performed with a distance target and 1.00 diopter (D) and 2.00 D accommodative targets and after administration of topical pilocarpine 4%. Agreement between PCI and AS-OCT ACD measurements and IOL movement was calculated.

RESULTS

Measurements were obtained in 18 patients. There was a consistent and statistically significant bias toward shallower ACD measurements with AS-OCT than with PCI, with the bias most pronounced after pilocarpine (mean 4.117 mm +/- 0.291 [SD] versus 4.054 +/- 0.287 mm; bias 0.063 mm; P<.0001). Limited IOL movement to 1.00 D and 2.00 D accommodative stimuli was detected with both instruments. After pilocarpine, forward IOL movement measurements were statistically significantly greater by AS-OCT than by PCI (mean 0.306 +/- 0.161 mm versus 0.270 +/- 0.155 mm) (P = .017).

CONCLUSIONS

The AS-OCT device showed a bias toward underestimation of ACD compared with the PCI device. The bias increased as ACD shallowed with pilocarpine, resulting in overestimation of forward IOL movement by AS-OCT. This may lead to overestimation of the accommodative performance of IOLs. The ACD measurements obtained by the 2 devices are not interchangeable.

Biconvex posterior chamber accommodating intraocular lens implantation after cataract surgery: long-term outcomes

PURPOSE

To evaluate the long-term efficacy of a biconvex accommodating intraocular lens (IOL) to restore near visual performance.

SETTING

Department of Ophthalmology, Keio University Hospital, Tokyo, Japan.

METHODS

This 4-year study comprised eyes that had cataract surgery with implantation of a 1CU accommodating IOL. At all postoperative visits, the following were assessed: subjective spherical equivalent (SE) refraction; uncorrected (UDVA) and corrected (CDVA) distance visual acuities; uncorrected (UNVA), distance-corrected (DCNVA), and corrected (CNVA) near visual acuities; change in minimum additional (add) power (diopters) to attain CNVA; and accommodation amplitude. A questionnaire was administered at the last visit.

RESULTS

Twelve eyes of 8 cataract patients (mean age 59.0 years +/- 18.4 [SD]) were evaluated. Postoperatively, the mean SE at 1 year and 4 years was significantly more hyperopic than at 1 month (P<.05). The mean UDVA increased significantly at 4 years compared with 1 month (P<.05). There were no significant changes in CDVA, UNVA, CNVA, and DCNVA throughout the follow-up period. The change in the minimum add power to attain CNVA and in the subjective and objective accommodation amplitudes also did not change significantly over time. Eighty-three percent of patients reported being satisfied with the results.

CONCLUSION

Four years after implantation of an accommodating IOL, most patients had good vision and were satisfied, although the accommodation amplitude for near vision was not sufficient throughout the follow-up.