Lens Accommodation Research Articles

We review the current state of our knowledge of the neural control of vergence and ocular accommodation in primates including humans. We first describe the critical need for these behaviors for viewing in a three-dimensional world. We then consider the sensory stimuli that drive vergence eye movements and lens accommodation and describe models of the sensorimotor transformations required to drive these motor systems. We discuss the interaction of vergence with saccades to produce high-speed shifts in gaze between objects at different distances and eccentricities. We also cover the normal development of these eye movements as well as the sequelae associated with their maldevelopment. In particular, we examine the neural substrates that produce vergence and lens accommodation, including motoneurons, immediate premotor circuitry, cerebellar and precerebellar regions, and cerebral cortical areas.

Purpose Presbyopia is an age-related condition characterized by diminished near-vision, primarily due to changes in the lens’ adaptive capacity. Shear Wave Ultrasound Elastography (SWE) offers a novel/noninvasive method to measure lens stiffness and could potentially enhance our understanding of presbyopia’s development. We aimed to use SWE to assess the elasticity of the human lens and explore the correlation between lens flexibility, age, presbyopia, and accommodation capacity. Methods A cross-sectional analysis was conducted with 84 participants (mean age = 39.61 ± 9.60) from a government hospital in Serdang, Selangor, Malaysia. Eligibility was confirmed through refractive error and visual acuity tests. Selected participants underwent SWE scanning, and measurements of accommodation and presbyopia were taken. Statistical analysis included descriptive summaries and Pearson correlation coefficients to examine relationships between lens elasticity age, presbyopia, and amplitude of accommodation. Results The analysis demonstrated a weak correlation between lens elasticity and age in nonpresbyopic group (r = 0.289) while positive strong correlation in presbyopic group (r = 0.674). A strong positive correlation was observed between lens elasticity and presbyopia in presbyopic group (r = 0.612). Moreover, there was a negative correlation with accommodation in both groups, (r = -0.358) for nonpresbyopic and (r = -0.493) presbyopic group. Conclusions While lens elasticity diminishes with age, changes in ocular biomechanical properties impact lens function, particularly affecting near vision. Importantly, SWE is found to be an effective tool for assessing age-related changes in lens elasticity and presbyopia across various age groups, highlighting its potential for broader clinical application in diagnosing and understanding presbyopia.

The purpose of this study was to investigate the in vivo biomechanical properties of crystalline lens nucleus and cortex in adults with myopia, their potential influences, and the correlation between these properties and ocular accommodation. The study included 195 right eyes of 195 participants, divided into 4 groups based on spherical equivalent: emmetropia (37 eyes), low myopia (41 eyes), moderate myopia (59 eyes), and high myopia (58 eyes). Participants underwent comprehensive ophthalmological examinations, including intraocular pressure, axial length, cycloplegic refraction, lens morphology, accommodation measurements, and Brillouin optical scanning of the lens. Additionally, demographic information, such as age and sex, was recorded. Normality tests were performed on the data using the Kolmogorov-Smirnov test. Between-group differences were examined using the Kruskal-Wallis test. Correlation and multiple regression analyses were conducted to analyze the factors associated with lens biomechanical properties and accommodation. The mean longitudinal modulus of the crystalline lens nucleus (LMN), anterior cortex (LMAC), and posterior cortex (LMPC) was 3.395 ± 0.027 GPa, 3.030 ± 0.066 GPa, and 2.990 ± 0.066 GPa, respectively, in adult myopia and 3.342 ± 0.024 GPa, 3.015 ± 0.0488 GPa, and 2.978 ± 0.049 GPa, respectively, in emmetropia. LMN was significantly higher in myopia (difference = 0.047, 95% confidence interval [CI] = 0.037 to 0.057, P < 0.001) and increased significantly with higher degrees of myopia (standardized β = -0.712, P < 0.001). No statistical differences in the LMAC or LMPC were observed between myopia and emmetropia. Lens densitometry on the centerline was the only lens parameter independently correlated with LMN (standardized β = -0.282, P < 0.01). Increased LMN in myopia was independently correlated with increased amplitude of accommodation (AMP) and decreased accommodative facility (AF; standardized β = 0.198, -0.237, all P < 0.05). LMN was significantly higher in adult patients with myopia than in emmetropia and increased with increasing myopia. Increased LMN in myopia significantly correlated with decreased AF and increased AMP. High LMN may be an important biological alteration during the development of adult myopia, especially high myopia, providing new insights into myopia pathogenesis.

Purpose: With age, there is an anterior shift of the ciliary body in the eye, which alters the angle of zonular insertion in older eyes compared with younger eyes. This study aims to simulate lens accommodation with different zonular angles to consider the influence of zonular position on lens accommodative capacity. Methods: Models were constructed based on lenses aged 11, 29, and 45 years using a 2D axisymmetric structure that included a capsule, cortex, nucleus, and zonular fibers. The different zonular fibers were simulated by changing the position of the point where the zonular fibers connect to the ciliary body. The effect of the different zonular fiber insertion angles on the model shape and optical power was analyzed. Results: The models show that smaller angles made by zonular fibers to the surface of the lens lead to larger optical power changes with simulated stretching. When the models were stretched, and when varying the zonule angles, the optical power of the 11-, 29-, and 45-year-old models changed up to 0.17 D, 0.24 D, and 0.30 D, respectively. The effect of zonular angles on the anterior radius of curvature of the anterior surface varied by 0.29 mm, 0.23 mm, and 0.25 mm for the 11-, 29-, and 45-year-old models, respectively. Conclusions: Larger zonular fiber insertion angles cause smaller deformation and less accommodative change, while parallel zonules induce the largest change in lens shape.

Background:A thin membrane capsule covers the eye lens and links the lens and the applied forces by the ciliary muscles. The capsule converts the tension of the concentrated zonules to distributed surface tractions over the cortex surface during the lens accommodation. The gradual changes of the capsule geometry and material properties with age and its important role in the design of intraocular lens implants were the motivation of extensive researches on describing the capsule biomechanical behavior.Aim:The present work aimed to study the lens accommodation response to different capsule thicknesses and material properties at different ages.Materials and Methods:A material and geometry parametric study was performed, drawing some guidelines on the choice of lens capsule thickness and biaxial/uniaxial material parameters and exploring the response sensitivity of the finite element model at different age groupsResults:The 16-, 35- and 48-year-old lenses were considered for lens accommodation simulation. The sensitivity of lens accommodation was studied at each age group by considering constant thickness (cnst-t) and variable thickness (var-t) capsules and biaxial (Biax) and uniaxial (Uniax) material characteristics tests. The lens was stretched through zonules, and corresponding absolute changes in central optical power (COP) were measured.Conclusion:After the stretch, the lens anterior and posterior curvatures increased, producing a change in COP. The Biax models underestimated the ΔCOP compared to the Uniax models. The 16-year lens model was more sensitive to material properties than thickness variation, while thickness variation was more relevant to the ΔCOP of the 35-year lens model. The 48-year model had the least sensitivity to capsule thickness and material property variations.

Purpose: To consider controversial issues of the mechanism of crystalline lens accommodation and to justify the hydraulic component in its implementation. Materials and Methods: Theories of the mechanism of accommodation and its assessment according to ultrasound biomicroscopy, magnetic resonance imaging and optical coherence tomography were analyzed. For the first time, the features of accommodative activation of intraocular fluid exchange in the closed hydrostatic system of the lens with the participation of mechanosensitive aquaporins were considered. When substantiating the hydraulic component in the mechanism of the crystalline lens accommodation, special emphasis was placed on the rapid decrease in pressure in the anterior and posterior chambers of the eye during contraction of the meridional portion of the ciliary muscle. Results: Analysis of various theories of accommodation has shown that mechanism of the crystalline lens its implementation continues to be discussed to this day. For the first time, the lens was considered as a unique closed hydrostatic system in which the pressure level is established through ultrafiltration and diffusion of intraocular fluid with the participation of aquaporins. Aquaporins form ion channels in the capsule, cuboidal epithelial cells, lens fibers and are mechanosensitive receptor proteins. The opening and closing of ion channels regulates the potassium-sodium pump, directed transport and exchange of intraocular fluid in the lens. The hydrostatic balance between the pressure in the crystalline lens and the anterior and posterior chambers of the eye is ensured by the crystalline lens capsule. The capsular bag of the crystalline lens can be considered as a curved diaphragm that separates two hydrostatic systems with different levels of pressure. Due to the hydrostatic buffering effect, the IOP level does not affect the crystalline lens, but it responds to a rapid decrease. This decrease in pressure in the anterior and posterior chambers is realized through the tension of the scleral spur by the meridional portion of the ciliary muscle and the activation of the valve mechanism of the scleral sinus. The greater the decrease in pressure, the more convex the crystalline lens takes on and increases its refraction. Conclusion: The presence of a hydraulic component in the mechanism of crystalline lens accommodation allows us to understand how the contraction of the small ciliary muscle can change the shape and refractive power of the large crystalline lens.

Safety, biocompatibility, and potential functionality of a new accommodative intraocular lens: An experimental study in rabbits

Oxidative stress represents one of the main factors driving the pathophysiology of multiple ophthalmic conditions including presbyopia, cataracts, dry eye disease (DED), glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy (DR). Currently, different studies have demonstrated the role of orally administered nutraceuticals in these diseases. For instance, they have demonstrated to improve lens accommodation in presbyopia, reduce protein aggregation in cataracts, ameliorate tear film stability, break up time, and tear production in dry eye, and participate in the avoidance of retinal neuronal damage and a decrease in intraocular pressure in glaucoma, contribute to the delayed progression of AMD, or in the prevention or treatment of neuronal death in diabetic retinopathy. In this review, we summarized the nutraceuticals which have presented a positive impact in ocular disorders, emphasizing the clinical assays. The characteristics of the different types of nutraceuticals are specified along with the nutraceutical concentration used to achieve a therapeutic outcome in ocular diseases.

Augmented reality (AR) is being used increasingly in a number of domains for task assistance. Evolving augmented reality solutions may require more than one display screen in certain scenarios. Switching between the display screens repeatedly, in order to gather information, would thus be required in such AR environments. Repeatedly switching between the display screens will require the users to change their attention continuously. Additionally, the eye lens will have to accommodate at different distances when viewing the information presented on multiple display screens. These repeated accommodation demands, to change the focus of the eye lens, will put additional strain on the accommodation mechanism of the eye, thereby increasing visual fatigue. Attention switching and increased accommodation demands will eventually affect human performance. The human visual system will also be affected by the amount of light it is exposed to. It is understandable that the brightness of the display in an AR environment with respect to the ambient light would affect the visual fatigue induced in the users and eventually impact their performance. This study was aimed at studying the effect of repeated eye lens accommodation, attention switching and display screen brightness on human performance and visual fatigue, under typical illumination conditions. It was observed that medium brightness level induced least visual fatigue and resulted in highest performance levels in a room well lit by LED luminaries. Repeated eye lens accommodation and attention switching, involved in screen switching, were found to induce visual fatigue and adversely affect human performance.

PurposeUnder real-world conditions, saccades are often accompanied by changes in vergence angle and lens accommodation that compensate for changes in the distance between the current fixation point and the next target. As the superior colliculus directs saccades, we examined whether it contains premotor neurons that might control lens compensation for target distance.MethodsRabies virus or recombinant rabies virus was injected into the ciliary bodies of Macaca fascicularis monkeys to label circuits controlling lens accommodation via retrograde transsynaptic transport. In addition, conventional anterograde tracers were used to confirm the rabies findings with respect to projections to preganglionic Edinger–Westphal motoneurons.ResultsAt time courses that rabies virus labeled lens-related premotor neurons in the supraoculomotor area and central mesencephalic reticular formation, labeled neurons were not found within the superior colliculus. They were, however, found bilaterally in the medial pretectal nucleus continuing caudally into the tectal longitudinal column, which lies on the midline, between the colliculi. A bilateral projection by this area to the preganglionic Edinger–Westphal nucleus was confirmed by anterograde tracing. Only at longer time courses were cells labeled in the superior colliculus.ConclusionsThe superior colliculus does not provide premotor input to preganglionic Edinger–Westphal nucleus motoneurons, but may provide input to lens-related premotor populations in the supraoculomotor area and central mesencephalic reticular formation. There is, however, a novel third population of lens-related premotor neurons in the tectal longitudinal column and rostrally adjacent medial pretectal nucleus. The specific function of this premotor population remains to be determined.

TRPV4: Cell type-specific activation, regulation and function in the vertebrate eye.

Temporal changes in accommodative responses to periodic visual motion

The purpose of this article is to review the current status of presbyopia amelioration with surgical and pharmacologic procedures that partially compensate for loss of accommodation in advance of cataract surgery and lens replacement. Over the last few years, several corneal surgical and topical pharmacological approaches for the treatment of presbyopia have been introduced to the marketplace or are in the developmental pipeline. The approaches vary in invasiveness, duration of effect, reversibility, risk/benefit ratio, and clinical results. The advantages and disadvantages for each are discussed. Corneal surgical interventions aim to provide improved near and intermediate vision in patients with presbyopia through refractive means that extend ocular depth of focus through shape modification. The use of miotic drops or corneal lamellar implants extend depth of focus with the "pinhole" aperture size reduction effect. Unlike in adults younger than 40 years, the refractive status of the patient with presbyopia is not stable. Hence, procedures that provide a permanent refractive change may not provide long-term full correction; eye drops or other treatments that are self-reversing in time or are easily reversible may be used as needed. On the horizon, procedures are being explored that may add years of functional lens accommodation by preserving the deformable gel properties of the lens. [J Refract Surg. 2021;37(6 Suppl):S20-S27.].

PurposeIn frontal-eyed mammals such as primates, eye movements are coordinated so that the lines of sight are directed at targets in a manner that adjusts for target distance. The lens of each eye must also be adjusted with respect to target distance to maintain precise focus. Whether the systems for controlling eye movements are monocularly or binocularly organized is currently a point of contention. We recently determined that the premotor neurons controlling the lens of one eye are bilaterally distributed in the midbrain. In this study, we examine whether this is due to premotor neurons projecting bilaterally to the preganglionic Edinger-Westphal nuclei, or by a mixture of ipsilaterally and contralaterally projecting cells supplying each nucleus.MethodsThe ciliary muscles of Macaca fasicularis monkeys were injected with recombinant forms of the N2c rabies virus, one eye with virus that produced a green fluorescent marker and the other eye with a virus that produced a red fluorescent marker.ResultsPreganglionic motoneurons in the Edinger-Westphal nucleus displayed the same marker as the ipsilateral injected muscle. Many of the premotor neurons in the supraoculomotor area and central mesencephalic reticular formation were doubly labeled. Others were labeled from either the ipsilateral or contralateral eye.ConclusionsThese results suggest that both monocular control and binocular control of lens accommodation are present. Binocular inputs yoke the accommodation in the two eyes. Monocular inputs may allow modification related to differences in each eye's target distance or differences in the capacities of the two ciliary muscles.

Oculomotor disorders are known to have profound impacts on a patients' quality of life. However, current clinical practice lacks the capability to provide simultaneous assessment of three tightly coupled oculomotor control components, i.e. eye movement, lens accommodation, and pupil response. In this study, a holographic waveguide (HW) based benchtop optometer was constructed and evaluated with a model eye. Experimental result and quantitative analysis indicate that a HW can convey high quality retinal images to a camera at an illumination level safe for human subjects and support high accuracy measurements of ocular refractive error over a wide range. Further development of a HW-based system promises a wearable, see-through device for comprehensive assessment of oculomotor control components while the subject is engaged in normal daily activities and thus enable advanced research and clinical management of oculomotor disorders.

The motor outflow for the pupillary light reflex originates in the preganglionic motoneuron subdivision of the Edinger–Westphal nucleus (EWpg), which also mediates lens accommodation. Despite their importance for vision, the morphology, ultrastructure and luminance-related inputs of these motoneurons have not been fully described in primates. In macaque monkeys, we labeled EWpg motoneurons from ciliary ganglion and orbital injections. Both approaches indicated preganglionic motoneurons occupy an EWpg organized as a unitary, ipsilateral cell column. When tracers were placed in the pretectal complex, labeled terminals targeted the ipsilateral EWpg and reached contralateral EWpg by crossing both above and below the cerebral aqueduct. They also terminated in the lateral visceral column, a ventrolateral periaqueductal gray region containing neurons projecting to the contralateral pretectum. Combining olivary pretectal and ciliary ganglion injections to determine whether a direct pupillary light reflex projection is present revealed a labeled motoneuron subpopulation that displayed close associations with labeled pretectal terminal boutons. Ultrastructurally, this subpopulation received synaptic contacts from labeled pretectal terminals that contained numerous clear spherical vesicles, suggesting excitation, and scattered dense-core vesicles, suggesting peptidergic co-transmitters. A variety of axon terminal classes, some of which may serve the near response, synapsed on preganglionic motoneurons. Quantitative analysis indicated that pupillary motoneurons receive more inhibitory inputs than lens motoneurons. To summarize, the pupillary light reflex circuit utilizes a monosynaptic, excitatory, bilateral pretectal projection to a distinct subpopulation of EWpg motoneurons. Furthermore, the interconnections between the lateral visceral column and olivary pretectal nucleus may provide pretectal cells with bilateral retinal fields.

To view a nearby target, the three components of the near response are brought into play: 1) the eyes are converged through contraction of the medial rectus muscles to direct both foveae at the target, 2) the ciliary muscle contracts to allow the lens to thicken, increasing its refractive power to focus the near target on the retina, and 3) the pupil constricts to increase depth of field. In this study, we utilized retrograde transsynaptic transport of the N2c strain of rabies virus injected into the ciliary body of one eye of macaque monkeys to identify premotor neurons that control lens accommodation. We previously used this approach to label a premotor population located in the supraoculomotor area. In the present report, we describe a set of neurons located bilaterally in the central mesencephalic reticular formation that are labeled in the same time frame as the supraoculomotor area population, indicating their premotor character. The labeled premotor neurons are mostly multipolar cells, with long, very sparsely branched dendrites. They form a band that stretches across the core of the midbrain reticular formation. This population appears to be continuous with the premotor near-response neurons located in the supraoculomotor area at the level of the caudal central subdivision of the oculomotor nucleus. The central mesencephalic reticular formation has previously been associated with horizontal saccadic eye movements, so these premotor cells might be involved in controlling lens accommodation during disjunctive saccades. Alternatively, they may represent a population that controls vergence velocity. NEW & NOTEWORTHY This report uses transsynaptic transport of rabies virus to provide new evidence that the central mesencephalic reticular formation (cMRF) contains premotor neurons controlling lens accommodation. When combined with other recent reports that the cMRF also contains premotor neurons supplying medial rectus motoneurons, these results indicate that this portion of the reticular formation plays an important role in directing the near response and disjunctive saccades when viewers look between targets located at different distances.

The aims: to study the physiological indices, which characterize the biological age (BA) of the woman, in the process of physiological pregnancy and conduct a correlation analysis between these indices and the stage of pregnancy in different age groups. Materials and methods. Total of 122 pregnant women aged 20-34 years with different gestational age were selected for the study; all participants underwent a comprehensive functional examination. From the obtained results, the BA values were calculated using the in-depth «Kiev» scale as well as our own modification. Results. Upon an increase in the gestational age, there were changes in the BA-related indices in women of various age groups; these changes pertained to the vascular wall stiffness, respiratory functions, static balancing and the lens accommodation ability. Conclusion. The absence of changes in the BA, as calculated according to our modified test, during physiological pregnancy, suggests its applicability to women of young reproductive age. This calculation approach can be recommended for further studies in obstetrics and gynecology.

The oculomotor (OM) complex is a combination of somatic and parasympatethic neurons. The correct development and wiring of this cranial pair is essential to perform basic functions: eyeball and eyelid movements, pupillary constriction, and lens accommodation. The improper formation or function of this nucleus leads pathologies such as strabismus. We describe the OM organization and function in different vertebrate brains, including chick, mouse, and human. The morphological localization is detailed, as well as the spatial relation with the trochlear nucleus in order to adjust some misleading anatomical topographic descriptions. We detailed the signaling processes needed for the specification of the OM neurons. The transcriptional programs driven the specification and differentiation of these neurons are partially determined. We summarized recent genetic studies that have led to the identification of guidance mechanisms involved in the migration, axon pathfinding, and targeting of the OM neurons. Finally, we overviewed the pathology associated to genetic malformations in the OM development and related clinical alterations. Anat Rec, 302:446-451, 2019. © 2018 Wiley Periodicals, Inc.

PurposeThese experiments were designed to reveal the location of the premotor neurons that have previously been designated physiologically as the midbrain near response cells controlling vergence, lens accommodation, and pupillary constriction in response to target distance.MethodsTo identify this population, the fixed N2c strain of rabies virus was injected into the ciliary body of seven Macaca fascicularis monkeys. The virus was trans-synaptically transported to the brain. Following a 58- to 76-hour survival, animals were perfused with formalin fixative. After frozen sectioning, tissue was reacted to reveal the location of the infected populations by use of a monoclonal anti-rabies antibody. Another series of sections was processed to determine which of the rabies-positive cells were cholinergic motoneurons by use of an antibody to choline acetyl transferase.ResultsAt earlier time points, only cholinergic cells in the preganglionic Edinger-Westphal nucleus ipsilateral to the injection were labeled. At later time points, an additional population of noncholinergic, premotor cells was present. These were most numerous at the caudal end of the supraoculomotor area, where they formed a bilateral band, oriented mediolaterally immediately above the oculomotor nucleus. Rostral to this, a smaller bilateral population was located near the midline within the supraoculomotor area.ConclusionsMost lens preganglionic motoneurons are multipolar cells making up a continuous column within the Edinger-Westphal nucleus. A population of premotor cells that likely represents the midbrain near response cells is located in the supraoculomotor area. These cells are bilaterally distributed relative to the eye they control, and are most numerous caudally.