Accommodative Lens Research Articles

A new look at an old problem: 3D modeling of accommodation reveals how age-related biomechanical changes contribute to dysfunction in presbyopia.

Presbyopia is an age-related ocular disorder where accommodative ability declines so that an individual's focusing range is insufficient to provide visual clarity for near and distance vision tasks without corrective measures. With age, the eye exhibits changes in biomechanical properties of many components involved in accommodation, including the lens, sclera, and ciliary muscle. Changes occur at different rates, affecting accommodative biomechanics differently, but individual contributions to presbyopia are unknown. We used a finite element model (FEM) of the accommodative mechanism to simulate age-related changes in lens stiffness, scleral stiffness, and ciliary contraction to predict differences in accommodative function. The FEM predicts how ciliary muscle action leads to lens displacement by initializing a tensioned unaccommodated lens (Phase 0) then simulating ciliary muscle contraction in accommodation (Phase 1). Model inputs were calibrated to replicate experimentally measured lens and ciliary muscle in 30-year-old eyes. Predictions of accommodative lens deformation were verified with additional imaging studies. Model variations were created with altered lens component stiffnesses, scleral stiffness, or ciliary muscle section activations, representing fifteen-year incremental age-related changes. Model variations predict significant changes in accommodative function with age-related biomechanical property changes. Lens changes only significantly altered lens thickening with advanced age (46% decrease at 75 years old) while sclera changes produced progressive dysfunction with increasing age (23%, 36%, 49% decrease at 45, 60, and 75 years old). Ciliary muscle changes effected lens position modulation. Model predictions identified potential mechanisms of presbyopia that likely work in combination to reduce accommodative function and could indicate effectiveness of treatment strategies and their dependency on patient age or relative ocular mechanical properties.

Clinical Effectiveness of Facility and Accuracy of Accommodation in Diagnosis of Non Strabismic Binocular Vision Anomalies in Young Adults: A Prospective Cross-sectional Observational Study

Introduction: Orthoptic evaluation is highly recommended in children and young adults to diagnose binocular dysfunctions. Binocular vision dysfunctions may hamper academic performance in children. Accommodative facility and accommodative accuracy are two orthoptic tests to evaluate accommodative flexibility and accommodative status of eye. Aim: To investigate the effectiveness of facility and accuracy of accommodation in diagnosis Non Strabismic Binocular Vision Anomalies (NSBVA) in young adults. Materials and Methods: This prospective, cross-sectional observational study was conducted at Optsight Eye Care in association with Amity Medical School, Gurugram, Haryana, India, from August 2020 to August 2021. A total of 175 subjects (both symptomatic and asymptomatic) with normal anterior and posterior segment findings, and aged between 18-25 years were evaluated for accommodative facility test with the help of accommodative lens flipper ±2D and for accommodative status test with the help of monocular estimation method (dynamic retinoscopy). Both the tests were done over their best corrected visual acuity after refractive error correction and the Pearson correlation test was applied to find out the correlation. Further, complete orthoptic examination was performed for all the subjects to correlate the abnormal findings from the two tests and conventional orthoptic tests. Independent sample t-test was applied to compare the accommodative facility between refractive groups. Results: Out of 175 subjects, 84 (48%) of the subjects were found to have NSBVA which included 26 (14.86%) Convergence insufficiency, 30 (17.14%) with accommodative insufficiency, 25 (14.29%) with convergence insufficiency secondary to accommodative insufficiency, and 3 (1.71%) with accommodative infacility. A positive correlation between binocular accommodative facility and status of accommodation was found with a p-value <0.001 (r=0.51). Conclusion: Status of accommodation and facility test can help to differentiate the accommodative and vergence problems making examination less time consuming. Both of these procedures should be a part of general routine eye examination protocol in the young adult group so that detection of these anomalies become less time consuming and patient gets benefitted from early intervention

The action of ciliary muscle contraction on accommodation of the lens explored with a 3D model

The eye's accommodative mechanism changes optical power for near vision. In accommodation, ciliary muscle excursion relieves lens tension, allowing it to return to its more convex shape. Lens deformation alters its refractive properties, but the mechanics of ciliary muscle actions are difficult to intuit due to the complex architecture of the tissues involved. The muscle itself comprises three sections of dissimilarly oriented cells. These cells contract, transmitting forces through the zonule fibers and extralenticular structures. This study aims to create a finite element model (FEM) to predict how the action of the ciliary muscle sections leads to lens displacement. The FEM incorporates initialization of the disaccommodated lens state and ciliary muscle contraction, with three muscle sections capable of independent activation, to drive accommodative movement. Model inputs were calibrated to replicate experimentally measured disaccommodated lens and accommodated ciliary muscle shape changes. Additional imaging studies were used to validate model predictions of accommodative lens deformation. Models were analyzed to quantify mechanical actions of ciliary muscle sections in lens deformation and position modulation. Analyses revealed that ciliary muscle sections act synergistically: the circular section contributes most to increasing lens thickness, while longitudinal and radial sections can oppose this action. Conversely, longitudinal and radial sections act to translate the lens anteriorly with opposition from the circular section. This FEM demonstrates the complex interplay of the three sections of ciliary muscle in deforming and translating the lens during accommodation, providing a useful framework for future investigations of accommodative dysfunction that occurs with age in presbyopia.

Determination of the hyperelastic material behavior of hydrogel specimens for expandable lens implants

Abstract Theoretical and experimental investigations were carried out for development of human lens implants made from hydrogel material. The material properties were measured and implemented in a Finite element model. Though the material is still too stiff for accommodative lenses, the theoretical and experimental foundations for the implant development were established.

Patient-centered and visual quality outcomes of premium cataract surgery: a systematic review.

Over 8 million cataract surgeries are performed in the United States and the European Union annually, with many patients choosing to pay out of pocket for premium options including premium intraocular lens implants (IOLs) or laser-assisted cataract surgery (LACS). This report provides a systematic review evaluating patient-centered and visual quality outcomes comparing standard monofocal IOLs to premium cataract surgery options. PubMed and EMBASE were searched for publications published between January 1, 1980, and September 18, 2016, on multifocal, accommodative, and toric IOLs, monovision, and LACS, which reported on 1) dysphotopsias, 2) contrast sensitivity, 3) spectacle independence, 4) vision-related quality of life or patient satisfaction, and 5) IOL exchange. Multifocal lenses achieved higher rates of spectacle independence compared to monofocal lenses but also had higher reported frequency of dysphotopsia and worse contrast sensitivity, especially with low light or glare. Accommodative lenses were not associated with reduced contrast sensitivity or more dysphotopsia but had only modest improvements in spectacle independence compared to monofocal lenses. Studies of monovision did not target a sufficiently myopic outcome in the near-vision eye to achieve the full potential for spectacle independence. Patients reported high levels of overall satisfaction regardless of implanted IOL. No studies correlated patient-reported outcomes with patient expectations. Studies are needed to thoroughly compare patient-reported outcomes with concomitant patient expectations. In light of the substantial patient costs for premium options, patients and their surgeons will benefit from a better understanding of which surgical options best meet patients' expectations and how those expectations can be impacted by premium versus monofocal-including monovision-options.

Accommodative movements of the lens/capsule and the strand that extends between the posterior vitreous zonule insertion zone & the lens equator, in relation to the vitreous face and aging.

To elucidate the dynamic accommodative movements of the lens capsule, posterior lens and the strand that attaches to the posterior vitreous zonule insertion zone and posterior lens equator (PVZ INS-LE), and their age-related changes. Twelve human subjects (ages 19-65years) and 12 rhesus monkeys (ages 6-27years) were studied. Accommodation was induced pharmacologically (humans) or by central electrical stimulation (monkeys). Ultrasound biomicroscopy was used to image intraocular structures in both species. Surgical procedures and contrast agents were utilized in the monkey eyes to elucidate function and allow visualization of the intraocular accommodative structures. Human: The posterior pole of the lens moves posteriorly during accommodation in proportion to accommodative amplitude and ciliary muscle movement. Monkey: Similar accommodative movements of the posterior lens pole were seen in the monkey eyes. Following extracapsular lens extraction (ECLE), the central capsule bows backward during accommodation in proportion to accommodative amplitude and ciliary muscle movement, while the peripheral capsule moves forward. During accommodation the ciliary muscle moved forward by ~1.0mm, pulling forward the vitreous zonule and the PVZ INS-LE structure. During the accommodative response the PVZ INS-LE structure moved forward when the lens was intact and when the lens substance and capsule were removed. In both the monkey and the human eyes these movements declined with age. The accommodative shape change of the central capsule may be due to the elastic properties of the capsule itself. For these capsule/lens accommodative posterior movements to occur, the vitreous face must either allow for it or facilitate it. The PVZ INS-LE structure may act as a 'strut' to the posterior lens equator (pushing the lens equator forward) and thereby facilitate accommodative forward lens equator movement and lens thickening. The age-related posterior restriction of the ciliary muscle, vitreous zonule and the PVZ-INS LE structure dampens the accommodative lens shape change. Future descriptions of the accommodative mechanism, and approaches to presbyopia therapy, may need to incorporate these findings.

Capsular opacification and accommodative lens refilling

SummaryAfter lens refilling with a silicone polymer, accommodation has been demonstrated in rhesus monkeys. However, coinciding with the development of capsular opacification the accommodative amplitude decreases to zero. Several strategies may be followed to prevent the development of capsular opacification. A straight forward strategy is the attempt to destroy remaining lens epithelial cells in the lens capsule by cytotoxic drugs. By isolating the lens capsular bag from the rest of the anterior chamber the lens capsule may be selectively treated with drugs. Our experiments in various animal models have shown that lens epithelial cells are very resistant to these treatments. This suggests that better strategies are needed. In further experiments we found that the choice of a proper biomaterial in the capsular bag may also significantly influence the capsular opacification response. Results of lens refilling with Hyaluronan and functionalized nanogels will be discussed.

Changes in lens stiffness due to capsular opacification in accommodative lens refilling

Accommodation may be restored to presbyopic lenses by refilling the lens capsular bag with a soft polymer. After this accommodative lens refilling prevention of capsular opacification is a requirement, since capsular opacification leads to a decreased clarity of the refilled lens. It has been hypothesized that capsular fibrosis causing the capsular opacification results in increased stiffness of the lens capsular bag, therewith contributing to a decrease in accommodative amplitude of the lens. However, the change in viscoelastic properties of refilled lenses due to capsular fibrosis has never been measured directly. In this study we examined natural lenses from enucleated porcine eyes and refilled lenses directly after refilling and after three months of culturing, when capsular fibrosis had developed, and determined their viscoelastic properties with a low load compression tester. Control refilled lenses were included in which capsular opacification was prevented by treatment with actinomycin D. We related lens stiffening to the degree of capsular opacification, as derived from the microscopic images taken with a confocal laser scanning microscope. Overall, the refilled lenses directly after refilling were softer than refilled lenses after three months of culturing, and refilled lenses treated with actinomycin D were softer compared with untreated refilled lenses. The degree of capsular opacification as assessed by microscopy corresponds to an increase in lens stiffness. This indicates that the viscoelastic properties of the refilled lens are influenced by capsular fibrosis and modulated by treatment of the lens epithelium. In conclusion, this study shows that the development of capsular fibrosis negatively affects the viscoelastic properties of isolated, cultured refilled lenses.

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

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

Extralenticular and Lenticular Aspects of Accommodation and Presbyopia in Human Versus Monkey Eyes

To determine if the accommodative forward movements of the vitreous zonule and lens equator occur in the human eye, as they do in the rhesus monkey eye; to investigate the connection between the vitreous zonule posterior insertion zone and the posterior lens equator; and to determine which components-muscle apex width, lens thickness, lens equator position, vitreous zonule, circumlental space, and/or other intraocular dimensions, including those stated in the objectives above-are most important in predicting accommodative amplitude and presbyopia. Accommodation was induced pharmacologically in 12 visually normal human subjects (ages 19-65 years) and by midbrain electrical stimulation in 11 rhesus monkeys (ages 6-27 years). Ultrasound biomicroscopy imaged the entire ciliary body, anterior and posterior lens surfaces, and the zonule. Relevant distances were measured in the resting and accommodated eyes. Stepwise regression analysis determined which variables were the most important predictors. The human vitreous zonule and lens equator move forward (anteriorly) during accommodation, and their movements decline with age, as in the monkey. Over all ages studied, age could explain accommodative amplitude, but not as well as accommodative lens thickening and resting muscle apex thickness did together. Accommodative change in distances between the vitreous zonule insertion zone and the posterior lens equator or muscle apex were important for predicting accommodative lens thickening. Our findings quantify the movements of the zonule and ciliary muscle during accommodation, and identify their age-related changes that could impact the optical change that occurs during accommodation and IOL function.

ALIGNMENT AND IMAGING OF AN EYE WITH AN ULTRASONIC SCANNER

A method and apparatus are disclosed for generating accurate and precise ultrasonic images of biological materials or animate objects, such as the cornea and lens of the eye, and, in particular, to an ultrasonic scanning apparatus that can position its virtual center of curvature such that its ultrasonic transducer will emit pulses that reflect substantially perpendicularly from a curved specular surface of interest within the eye. This invention can allow real time imaging of a lens as it accommodates and can better enable researchers and ophthalmic surgeons to develop, fit, implant and diagnose performance of accommodative lenses.

Trends in anterior segment surgery: what is coming?

AbstractAnterior segment surgery has experienced a huge development in the last 25 years. Presently, in spite of this accelerated development, new technologies have emerged that have impacted considerably the surgery of the crystalline lens, the cornea and its pathologies. Corneal blindness, corneal debilitating diseases (corneal ectatic disease), corneal opacities, post infectious or traumatic problems and complication of cataract surgery has increased the rate of performance of corneal surgery, with corneal blindness still being a worldwide problem. Concerning the crystalline lens, cataract surgery is the most widely performed surgical procedure in the human being, and every step forward in this surgery affects millions of people around the world every year. Corneal surgery has been opened to a new stage of development thanks to the introduction of femtosecond laser technology, corneal crosslinking procedures, better knowledge of corneal biomechanics, improvements in corneal transplantation, development of corneal regenerating techniques, new antiinflammatory and immunological medication and a better knowledge about the ocular surface biological behaviour. Crystalline lens and cataract surgery have experienced a major recent impact with the introduction of femtosecond lasers for cataract surgery, and the so‐called premium IOLs. Jointly, they represent a large step forward in the outcomes that are expected for cataract surgery, in which not only vision research is expected but also the spectacle independent condition for far and for near. Different models of accommodative lenses, multifocal lenses and other technologies have approached this refractive purpose. In this presentation the actual trends based on evidence based knowledge about the immediate evolution of corneal and crystalline lens surgery, the recent developments in the knowledge of the corneal diopter in normal and diseased conditions and the implementation that cataract surgery and IOL technology is undergoing today will be explained. The concept of eye modelling with modern customization of all these procedures through a global modern eye based on recent knowledge will be also outlined.

Organic–inorganic nanocomposite gels as an in situ gelation biomaterial for injectable accommodative intraocular lens

We focus on the development of a novel injectable accommodative lens for intraocular applications, which is based on a thermosensitive hydrophobically modified poly(ethylene glycol) (HM-PEG) containing hydrophilized silica nanoparticles. We distinguished macroscopically, with changes in the temperature or concentration, two regions in the phase diagram for aqueous solution of HM-PEG: transparent sol and transparent gel. These changes occurred reversibly, without hysteresis, when the temperature was decreased. The temperature and concentration regime in which the gel formed are reduced by adding silica nanoparticles into the gel matrix. Small-angle neutron scattering measurements for nanocomposite gels provide good proof of a gel phase where the high shear-modulus is gained by a high inter-micellar correlation originating in the crystalline order. Under the condition of uniform distribution of silica nanoparticles with small size (2–5 nm) in the gel matrix, an increase in the refractive index up to 0.0667 was obtained for the nanocomposite gel compared with the native gel matrix without an increase in turbidity. This composite system could be formulated to match the modulus and the refractive index of the natural lens (∼1.411), and was easily extruded through a narrow-gauge needle. Rapid endocapsular gelation yielded an optically clear gel within the lens capsular bag. This technique enables us to validate methods to determine the biomechanics of the lens and its role in accommodation. The modification of the mechanical response and stability of the HM-PEG network by addition of silica nanoparticles was also investigated in detail.

Challenges and approaches in modern biometry and IOL calculation

The introduction of new intraocular lenses (IOLs), industry marketing to the public and patient expectations has warranted increased accuracy of IOL power calculations. Toric IOLs, multifocal IOLs, aspheric IOLs, phakic lenses, accommodative lenses, cases of refractive lens exchange and eyes that have undergone previous refractive surgery all require improved clinical measurements and IOL prediction formulas. Hence, measurement techniques and IOL calculation formulas are essential factors that affect the refractive outcome.Measurement with ultrasound has been the historic standard for measurement of ocular parameters for IOL calculation. However the introduction of optical biometry using partial coherence interferometry (PCI) has steadily established itself as the new standard. Additionally, modern optical instruments such as Scheimpflug cameras and optical coherence tomographers are being used to determine corneal power that was normally the purview of manual keratometry and topography.A number of methods are available to determine the IOL power including the empirical, analytical, numerical or combined methods. Ray tracing techniques or paraxial approximation by matrix methods or classical analytical ‘IOL formulas’ are actively used in for the prediction of IOL power. There is no universal formula for all cases – phakic and pseudophakic cases require different approaches, as do short eyes, long eyes, astigmatic eyes or post-refractive surgery eyes. Invariably, IOLs are characterized by different methods and lens constants, which require individual optimization. This review describes the current methods for biometry and IOL calculation.

Prevention of capsular opacification after accommodative lens refilling surgery in rabbits

Silicone gel-like polymers have been proposed to replace the cataractous lens and therewith restore both vision and accommodation. Lens replacement is associated with opacification of the capsular bag due to the lens epithelial cell response. In this study, the in vivo effectiveness of a 5 min treatment with actinomycin D and/or cycloheximid to prevent the development of capsular opacification after filling the capsular bag with a silicone polymer as an accommodating lens was studied. It was found that treating the inside of the capsular bag with a solution containing actinomycin D reduced the development of visible capsular opacification for three months. In some animals, the lens capsules were completely clear, indicating the potential of this method. Side effects of the treatment in the form of visible cornea opacification occurred and ranged from mild to severe in some animals, while in other animals no toxicity occurred. This indicates that a safe application of the cytotoxic substances is feasible. In view of the side effects and the fact that not all lens capsules of the animals treated with actinomycin D were clear, improvements in the methods used are necessary and seem to be possible.

Real and Pseudoaccommodation in Accommodative Lenses

In the attempt to manage presbyopia, different intraocular lens designs have been proposed such as monofocal IOLs with monovision or multifocal IOLs. Even though the lenses mentioned offer satisfactory visual results, contemporary ophthalmology has not completely answered the presbyopic dilemma by simulating the accommodative properties of the crystalline lens itself. Accommodative IOLs were designed to fill this gap and provide satisfactory vision for all distances by restoring some degree of “pseudoaccommodation.” Pseudo accommodative capability can be linked to monofocal IOL's as well but the results are not satisfactory enough to fully support unaided near vision. Pseudoaccommodation is a complex phenomenon that can be attributed to several static (i.e., pupil size, against-the-rule cylindrical refractive error, multifocality of the cornea) and dynamic (i.e., anterior movement of the implant itself) factors. Objective measurement of the accommodative capability offered by the accommodative IOLs is extremely difficult to obtain, and different methods such as autorefractometers, retinoscopy, and ultrasound imaging during accommodative effort, ray tracing, or pharmacological stimulation have been developed but the results are sometimes inconsistent. Despite the difficulties in measuring accommodation, accommodative IOLs represent the future in the attempt to successfully “cure” presbyopia.

Analysis and applications of accommodative lenses for vision corrections

Analysis and applications of vision correction via accommodating intraocular lens (AIOL) are presented. By Gaussian optics, analytic formulas for the accommodation rate function (M) for two-optics and three-optics systems are derived and compared with the exact numerical results. In a single-optics AIOL, typical value of M is (0.5-1.5) D∕mm, for an IOL power of (10-20) diopter. For a given IOL power, higher M is achieved in positive-IOL than negative-IOL. In the dual-optics AIOL, maximum accommodation is predicted when the front positive-optics moves toward the corneal plan and the back negative-optics moves backward. Our analytic formulas predict that greater accommodative rate may be achieved by using a positive-powered front optics, a general feature when either front or back optics is mobile. The M function is used to find the piggy-back IOL power for customized design based on the individual ocular parameters. Many of the new features demonstrated in this study can be easily realized by our analytic formulas, but not by raytracing method.

Nocturnality constrains morphological and functional diversity in the eyes of reef fishes

BackgroundAmbient light levels are often considered to drive the evolution of eye form and function. Diel activity pattern is the main mechanism controlling the visual environment of teleost reef fish, with day-active (diurnal) fish active in well-illuminated conditions, whereas night-active (nocturnal) fish cope with dim light. Physiological optics predicts several specific evolutionary responses to dim-light vision that should be reflected in visual performance features of the eye.ResultsWe analyzed a large comparative dataset on morphological traits of the eyes in 265 species of teleost reef fish in 43 different families. The eye morphology of nocturnal reef teleosts is characterized by a syndrome that indicates better light sensitivity, including large relative eye size, high optical ratio and large, rounded pupils. Improved dim-light image formation comes at the cost of reduced depth of focus and reduction of potential accommodative lens movement. Diurnal teleost reef fish, released from the stringent functional requirements of dim-light vision have much higher morphological and optical diversity than nocturnal species, with large ranges of optical ratio, depth of focus, and lens accommodation.ConclusionsPhysical characteristics of the environment are an important factor in the evolution and diversification of the vertebrate eye. Both teleost reef fish and terrestrial amniotes meet the functional requirements of dim-light vision with a similar evolutionary response of morphological and optical modifications. The trade-off between improved dim-light vision and reduced optical diversity may be a key factor in explaining the lower trophic diversity of nocturnal reef teleosts.

Microindentation of the Young Porcine Ocular Lens

Debate regarding the mechanisms of how the eye changes focus (accommodation) and why this ability is lost with age (presbyopia) has recently been rejoined due to the advent of surgical procedures for the correction of presbyopia. Due to inherent confounding factors in both in vivo and in vitro measurement techniques, mechanical modeling of the behavior of the ocular lens in accommodation has been attempted to settle the debate. However, a paucity of reliable mechanical property measurements has proven problematic in the development of a successful mechanical model of accommodation. Instrumented microindentation was utilized to directly measure the local elastic modulus and dynamic response at various locations in the lens. The young porcine lens exhibits a large modulus gradient with the highest modulus appearing at the center of the nucleus and exponentially decreasing with distance. The loss tangent was significantly higher in the decapsulated lens and the force waveform amplitude decreased significantly upon removal of the lens capsule. The findings indicate that localized measurements of the lens' mechanical properties are necessary to achieve accurate quantitative parameters suitable for mechanical modeling efforts. The results also indicate that the lens behaves as a crosslinked gel rather than as a collection of individual arched fiber cells.

Accommodative intraocular lenses: considerations on use, function and design

To review the development, design and clinical implications of the first US Food and Drugs Administration approved accommodative lens. To inform the reader of forthcoming accommodative intraocular lens technologies that are being clinically tested and other technologies that are under design. We present clinical data that are currently available or pending release on accommodative intraocular lenses. As much as the results of the technology can be appreciated, the approach toward the refractive mindset of the presbyopic intraocular lens patient must be understood and mastered. Accommodative intraocular lens design and development are at a feverish pace. The lure is the perceived holy grail for the solution of presbyopia.