Automated Compression Testing of the Ocular Lens

The biomechanical properties of the ocular lens are essential to its function as a variable power optical element. These properties change dramatically with age in the human lens, resulting in a loss of near vision called presbyopia. However, the mechanisms of these changes remain unknown. Lens compression offers a relatively simple method for assessing the lens' biomechanical stiffness in a qualitative sense and, when coupled with appropriate analytical techniques, can help quantify biomechanical properties. A variety of lens compression tests have been performed to date, including both manual and automated, but these methods inconsistently apply key aspects of biomechanical testing such as preconditioning, loading rates, and time between measurements. This paper describes a fully automated lens compression test wherein a motorized stage is synchronized with a camera to capture the force, displacement, and shape of the lens throughout a preprogrammed loading protocol. A characteristic elastic modulus may then be calculated from these data. While demonstrated here using porcine lenses, the approach is appropriate for the compression of lenses of any species.

A method for generating zonular tension in the murine eye by embedding and compressing the globe in a hydrogel

The ocular lens is the primary organ within the eye responsible for accommodation. During accommodation, the lens is subject to biomechanical forces. We previously demonstrated that stretching the porcine lens can increase lens epithelial cell proliferation. Although murine lenses are commonly employed in lens research, murine lens stretching has remained unexplored. Murine lens stretching thus represents a novel source of potential discovery in lens research. In the present study, we describe a method for stretching the murine lens by compressing the murine globe embedded in a hydrogel. We hypothesized that, as the eye is compressed along the optic axis, the lens would stretch through zonular tension due to the equatorial region of the eye bulging outward. Our results showed that this led to a compression-dependent increase in murine lens epithelial cell proliferation, suggesting that compression of the embedded murine globe is a viable technique for studying the mechanobiology of the lens epithelium.

Orbital fat swelling: A biomechanical theory and supporting model for spaceflight-associated neuro-ocular syndrome (SANS)

Spaceflight-Associated Neuro-ocular Syndrome (SANS) is a descriptor of several ocular and visual signs and symptoms which commonly afflicts those exposed to microgravity. We propose a new theory for the driving force leading to the development of Spaceflight-Associated Neuro-ocular Syndrome which is described via a finite element model of the eye and orbit. Our simulations suggest that the anteriorly directed force produced by orbital fat swelling is a unifying explanatory mechanism for Spaceflight-Associated Neuro-ocular Syndrome, as well as producing a larger effect than that generated by elevation in intracranial pressure. Hallmarks of this new theory include broad flattening of the posterior globe, loss of tension in the peripapillary choroid, decreased axial length, consistent with findings in astronauts. A geometric sensitivity study suggests several anatomical dimensions may be protective against Spaceflight-Associated Neuro-ocular Syndrome.

Oxidative stress in the brain and retina after traumatic injury

The brain and the retina share many physiological similarities, which allows the retina to serve as a model of CNS disease and disorder. In instances of trauma, the eye can even indicate damage to the brain via abnormalities observed such as irregularities in pupillary reflexes in suspected traumatic brain injury (TBI) patients. Elevation of reactive oxygen species (ROS) has been observed in neurodegenerative disorders and in both traumatic optic neuropathy (TON) and in TBI. In a healthy system, ROS play a pivotal role in cellular communication, but in neurodegenerative diseases and post-trauma instances, ROS elevation can exacerbate neurodegeneration in both the brain and the retina. Increased ROS can overwhelm the inherent antioxidant systems which are regulated via mitochondrial processes. The overabundance of ROS can lead to protein, DNA, and other forms of cellular damage which ultimately result in apoptosis. Even though elevated ROS have been observed to be a major cause in the neurodegeneration observed after TON and TBI, many antioxidants therapeutic strategies fail. In order to understand why these therapeutic approaches fail further research into the direct injury cascades must be conducted. Additional therapeutic approaches such as therapeutics capable of anti-inflammatory properties and suppression of other neurodegenerative processes may be needed for the treatment of TON, TBI, and neurodegenerative diseases.

A Review of Lens Biomechanical Contributions to Presbyopia

Purpose: Presbyopia-the progressive loss of near focus with age-is primarily a result of changes in lens biomechanics. In particular, the shape of the ocular lens in the absence of zonular tension changes significantly throughout adulthood. Contributors to this change in shape are changes in lens biomechanical properties, continuous volumetric growth lens, and possibly remodeling of the lens capsule. Knowledge in this area is growing rapidly, so the purpose of this mini-review was to summarize and synthesize these gains.Methods: We review the recent literature in this field.Results: The mechanisms governing age-related changes in biomechanical properties remains unknown. We have recently shown that lens growth may be driven by zonular tension. The same mechanobiological mechanism driving lens growth may also lead to remodeling of the capsule, though this remains to be demonstrated.Conclusions: This mini-review focuses on identifying mechanisms which cause these age-related changes, suggesting future work which may elucidate these mechanisms, and briefly discusses ongoing efforts to develop a non-surgical approach for therapeutic management of presbyopia. We also propose a simple model linking lens growth and biomechanical properties.

The Roles of Vitreous Biomechanics in Ocular Disease, Biomolecule Transport, and Pharmacokinetics

PURPOSE

The biomechanical properties of the vitreous humor and replication of these properties to develop substitutes for the vitreous humor have rapidly become topics of interest over the last two decades. In particular, the behavior of the vitreous humor as a viscoelastic tissue has been investigated to identify its role in a variety of processes related to biotransport, aging, and age-related pathologies of the vitreoretinal interface.

METHODS

A thorough search and review of peer-reviewed publications discussing the biomechanical properties of the vitreous humor in both human and animal specimens was conducted. Findings on the effects of biomechanics on vitreoretinal pathologies and vitreous biotransport were analyzed and discussed.

RESULTS

The pig and rabbit vitreous have been found to be most mechanically similar to the human vitreous. Age-related liquefaction of the vitreous creates two mechanically unique phases, with an overall effect of softening the vitreous. However, the techniques used to acquire this mechanical data are limited by the in vitro testing methods used, and the vitreous humor has been hypothesized to behave differently in vivo due in part to its swelling properties. The impact of liquefaction and subsequent detachment of the vitreous humor from the posterior retinal surface is implicated in a variety of tractional pathologies of the retina and macula. Liquefaction also causes significant changes in the biotransport properties of the eye, allowing for significantly faster movement of molecules compared to the healthy vitreous. Recent developments in computational and ex vivo models of the vitreous humor have helped with understanding its behavior and developing materials capable of replacing it.

CONCLUSIONS

A better understanding of the biomechanical properties of the vitreous humor and how these relate to its structure will potentially aid in improving clinical metrics for vitreous liquefaction, design of biomimetic vitreous substitutes, and predicting pharmacokinetics for intravitreal drug delivery.

Arvcf Dependent Adherens Junction Stability is Required to Prevent Age-Related Cortical Cataracts

The etiology of age-related cortical cataracts is not well understood but is speculated to be related to alterations in cell adhesion and/or the changing mechanical stresses occurring in the lens with time. The role of cell adhesion in maintaining lens transparency with age is difficult to assess because of the developmental and physiological roles that well-characterized adhesion proteins have in the lens. This report demonstrates that Arvcf, a member of the p120-catenin subfamily of catenins that bind to the juxtamembrane domain of cadherins, is an essential fiber cell protein that preserves lens transparency with age in mice. No major developmental defects are observed in the absence of Arvcf, however, cortical cataracts emerge in all animals examined older than 6-months of age. While opacities are not obvious in young animals, histological anomalies are observed in lenses at 4-weeks that include fiber cell separations, regions of hexagonal lattice disorganization, and absence of immunolabeled membranes. Compression analysis of whole lenses also revealed that Arvcf is required for their normal biomechanical properties. Immunofluorescent labeling of control and Arvcf-deficient lens fiber cells revealed a reduction in membrane localization of N-cadherin, β-catenin, and αN-catenin. Furthermore, super-resolution imaging demonstrated that the reduction in protein membrane localization is correlated with smaller cadherin nanoclusters. Additional characterization of lens fiber cell morphology with electron microscopy and high resolution fluorescent imaging also showed that the cellular protrusions of fiber cells are abnormally elongated with a reduction and disorganization of cadherin complex protein localization. Together, these data demonstrate that Arvcf is required to maintain transparency with age by mediating the stability of the N-cadherin protein complex in adherens junctions.

Tunable alginate hydrogels as injectable drug delivery vehicles for optic neuropathy

Many disease pathologies, particularly in the eye, are induced by oxidative stress. In particular, injury to the optic nerve (ON), or optic neuropathy, is one of the most common causes of vision loss. Traumatic optic neuropathy (TON) occurs when the ON is damaged following blunt or penetrating trauma to either the head or eye. Currently, there is no effective treatment for TON, only management options, namely the systematic delivery of corticosteroids and surgical decompression of the optic nerve. Unfortunately, neither option alleviates the generation of reactive oxygen species (ROS) which are responsible for downstream damage to the ON. Additionally, the systemic delivery of corticosteroids can cause fatal off‐target effects in cases with brain involvement. In this study, we developed a tunable injectable hydrogel delivery system for local methylene blue (MB) delivery using an internal method of crosslinking. MB was chosen due to its ROS scavenging ability and neuroprotective properties. Our MB‐loaded polymeric scaffold demonstrated prolonged release of MB as well as in situ gel formation. Additionally, following rheological characterization, these alginate hydrogels demonstrated minimal cytotoxicity to human retinal pigment epithelial cells in vitro and exhibited injection feasibility through small‐gauge needles. Our chosen MB concentrations displayed a high degree of ROS scavenging following release from the alginate hydrogels, suggesting this approach may be successful in reducing ROS levels following ON injury, or could be applied to other ocular injuries.

The Shape of Corneal Deformation Alters Air Puff–Induced Loading

Purpose: To determine the dynamic modification of the load exerted on the eye during air-puff testing by accounting for the deformation of the cornea.

Methods: The effect of corneal load alteration with surface shape (CLASS) was characterized as an additional component of the load produced during the concave phase where the fluid outflow tangential to the corneal surface creates backward pressure. Concave phase duration (t_CD), maximum CLASS value (CLASS_max), and the area under CLASS-time curve (CLASS_int) are calculated for 26 keratoconic (KCN), 102 normal (NRL), and 29 ocular hypertensive (OHT) subjects. Tukey’s HSD tests were performed to compare the three subject groups. A p-value less than 0.05 was considered statistically significant.

Results: Accounting for CLASS increased the load by 34.6% ± 7.7% at maximum concavity; these differences were greater in KCN subjects (p < 0.0001) and lower in OHT subjects (p = 0.0028) than in NRL subjects. t_CD and CLASS_int were significantly longer and larger, respectively, for KCN subjects than those in the NRL and OHT groups (p < 0.0001).

Conclusion: Load characterization is an essential step in assessing the cornea’s biomechanical response to air-puff–induced deformation. The dynamic changes in the corneal surface shape significantly alter the load experienced by the corneal apex. This implies a subject-specific loading dynamic even if the air puff itself is identical. This is important when comparing the same eye after a surgical procedure or topical medication that alters corneal properties. Stiffer corneas are least sensitive to a change in load, while more compliant corneas show higher sensitivity.

Hydrodynamic Interaction Between Tear Film and Air Puff From Noncontact Tonometry

Purpose

The purpose of this study was to investigate the mechanism of potential droplet formation in response to air puff deformation with two noncontact tonometers (NCTs).

Methods

Twenty healthy volunteers were examined using two NCTs, Ocular Response Analyzer and Corvis ST, and two contact tonometers, iCare and Tono-Pen. High-speed videos of the tear film response were captured with at spatial resolution of 20 microns/pixel at 2400 fps. Droplet size, droplet velocity, distance between air puff impact location, and the tear meniscus-lid margin were characterized.

Results

One subject was excluded due to technical issues. Droplets were detected only in tests with instilled eye drop. Videos showed the tear film rolls away from the apex while remaining adherent to the ocular surface due to the tendency of the fluid to remain attached to a solid surface explained by the Coanda effect. Twelve out of 38 videos with an eye drop administration showed droplet formation. Only one resulted in droplets with predominantly forward motion, which had the shortest distance between air puff impact location and lower meniscus. This distance on average was 5.9 ± 1.1 mm. The average droplet size was 500 ± 200 µm.

Conclusions

Results indicate no droplet formation under typical clinical setting. Hence, standard clinical use of NCT tests is not expected to cause droplets. NCT testing with eye drop administration showed droplet formation at the inferior eyelid boundary, which acts as a barrier and interrupts tear flow.

Translational Relevance

Study of tear film interaction with NCT air puff shows that these tonometers are not expected to cause droplet formation in standard use and that if external drops are required, both eyelids should be held if patients need assistance to maintain open eyes to avoid droplets with predominantly forward motion.

Latent-transforming growth factor beta-binding protein-2 (LTBP-2) is required for longevity but not for development of zonular fibers

Latent-transforming growth factor beta-binding protein 2 (LTBP-2) is a major component of arterial and lung tissue and of the ciliary zonule, the system of extracellular fibers that centers and suspends the lens in the eye. LTBP-2 has been implicated previously in the development of extracellular microfibrils, although its exact role remains unclear. Here, we analyzed the three-dimensional structure of the ciliary zonule in wild type mice and used a knockout model to test the contribution of LTBP-2 to zonule structure and mechanical properties. In wild types, zonular fibers had diameters of 0.5-1.0 micrometers, with an outer layer of fibrillin-1-rich microfibrils and a core of fibrillin-2-rich microfibrils. LTBP-2 was present in both layers. The absence of LTBP-2 did not affect the number of fibers, their diameters, nor their coaxial organization. However, by two months of age, LTBP-2-depleted fibers began to rupture, and by six months, a fully penetrant ectopia lentis phenotype was present, as confirmed by in vivo imaging. To determine whether the seemingly normal fibers of young mice were compromised mechanically, we compared zonule stress/strain relationships of wild type and LTBP-2-deficient mice and developed a quasi-linear viscoelastic engineering model to analyze the resulting data. In the absence of LTBP-2, the ultimate tensile strength of the zonule was reduced by about 50%, and the viscoelastic behavior of the fibers was altered significantly. We developed a harmonic oscillator model to calculate the forces generated during saccadic eye movement. Model simulations suggested that mutant fibers are prone to failure during rapid rotation of the eyeball. Together, these data indicate that LTBP-2 is necessary for the strength and longevity of zonular fibers, but not necessarily for their formation.

Accommodative tissues influence the shape of the cornea and potentially drive corneal morphogenesis

This study investigates whether the presence of accommodative tissues biomechanically influences the shape of the cornea and potentially drives corneal morphogenesis during embryonic ocular development. Porcine eyes were subjected to an internal pressure simulating intraocular pressure. Ocular geometry was evaluated using a corneal topographer and digital cameras before and after dissection of the accommodative tissues. A computational model of the porcine eye was constructed and loaded by an internal pressure representing intraocular pressure. Eye shape was evaluated in models with and without the ciliary body. The porcine model was generalized to the human model, simplified model, or embryonic model with different ocular tissue shapes, sizes, and stiffnesses. Experimental data showed that, even in the six-month-old pig eye, the average corneal radius of curvature increased after the removal of accommodative tissues compared to sham controls (p = 0.002). Computational results agreed with the experimental data and further suggested that the change in corneal radius is greater when the tissue stiffness is low and the intraocular pressure is high, regardless of the geometry and size of the eye components. Using a combined in vitro and in silico approach, this study explores the biomechanical influence of the accommodative tissues and related loads on the cornea and offers additional factors that might influence the shape of the cornea.

Biomechanical contribution of the sclera to dynamic corneal response in air-puff induced deformation in human donor eyes

This study was conducted to evaluate the impact of varying scleral material properties on the biomechanical response of the cornea under air-puff induced deformation. Twenty pairs of human donor eyes were obtained for this study. One eye from each pair had its sclera stiffened using 4% glutaraldehyde, while the fellow eye served as control for uniaxial strip testing. The whole globes were mounted in a rigid holder and intraocular pressure (IOP) was set using a saline column. Dynamic corneal response parameters were measured before and after scleral stiffening using the CorVis ST, a dynamic Scheimpflug analyzer. IOP was set to 10, 20, 30, and 40 mmHg, with at least 3 examinations performed at each pressure step. Uniaxial tensile testing data were fit to a neo-Hookean model to estimate the Young's modulus of treated and untreated sclera. Scleral Young's modulus was found to be significantly correlated with several response parameters, including Highest Concavity Deformation Amplitude, Peak Distance, Highest Concavity Radius, and Stiffness Parameter-Highest Concavity (SP-HC). There were significant increases in SP-HC after scleral stiffening at multiple levels of IOP, while no significant difference was observed in the corneal Stiffness Parameter - Applanation 1 (SP-A1) at any level of IOP. Scleral mechanical properties significantly influenced the corneal deformation response to an air-puff. The stiffer the sclera, the greater the constraining effect on corneal deformation resulting in lower displaced amplitude. This may have important clinical implications and suggests that both corneal and scleral material properties contribute to the observed corneal response in air-puff induced deformation.

Lens Stretching Modulates Lens Epithelial Cell Proliferation via YAP Regulation

Purpose

The continuous growth of the lens throughout life may contribute to the onset of age-related conditions in the lens (i.e., presbyopia and cataract). Volumetric growth is the result of continuous proliferation of lens epithelial cells (LECs). The driving factors controlling LEC proliferation are not well understood. This study tested the hypothesis that mechanical stretching modulates LEC proliferation.

Methods

Biomechanical regulation of LEC proliferation was investigated by culturing whole porcine lenses and connective tissues ex vivo under varying physiologically relevant stretching conditions using a bespoke lens stretching device. Additionally, some lenses were treated with a YAP function inhibitor to determine the Hippo signaling pathway's role in regulating lens growth. Resulting changes in LEC labeling index were analyzed using EdU incorporation and flow cytometry for each lens.

Results

LEC proliferation was found to be modulated by mechanical strain. Increasing both the magnitude of static stretching and the stretching frequency in cyclic stretching resulted in a proportional increase in the labeling indices of the LECs. Additionally, treatment with the YAP function inhibitor effectively eliminated this relationship.

Conclusions

These data demonstrate that LEC proliferation is regulated in part, by the mechanotransduction of stresses induced in the lens capsule and that YAP plays an important role in mechanosensing. These results have important implications for understanding lens growth and morphogenesis. The model may also be used to identify and evaluate targets for modulating lens growth.

Altered expression of aquaporin 1 and aquaporin 5 in the cornea after primary blast exposure

PURPOSE

Our study aimed to determine whether the altered expression of biomarkers linked to corneal injuries, such as the edema-regulating proteins aquaporin-1 and aquaporin-5 (AQP1 and AQP5), occurred following primary blast exposure.

METHODS

Adult male Dutch Belted rabbits were anesthetized and exposed to blast waves with peak overpressures of 142.5-164.1 kPa (20.4-23.4 psi). These exposure groups experienced peak blast overpressure-specific impulses (impulse per unit surface area) of 199.6-228.5 kPa-ms. Unexposed rabbits were included as controls. The animals were euthanized at 48 h post-exposure. Corneas obtained from the euthanized blast-exposed and control rabbits were processed for quantitative PCR and western blot to quantify mRNA and the protein expression of AQP1 and AQP5. Immunohistochemical analysis was conducted to determine the cellular localization of AQP1 and AQP5.

RESULTS

Corneal thickness increased up to 18% with the peak blast overpressure-specific impulses of 199.6-228.5 kPa-ms at 48 h after blast exposure. mRNA levels of AQP1 and AQP5 increased in the whole cornea lysates of blast-exposed rabbits relative to those of the controls. Western blot analyses of whole cornea lysates revealed that the expression levels of AQP1 and AQP5 were approximately 2- and 1.5-fold higher, respectively, in blast-exposed rabbits compared to controls. The extent of AQP1 immunostaining (AQP1-IS) increased in the epithelial cell layer after blast exposure. The AQP5-IS pattern changed from a mixed membrane and cytoplasmic expression in the controls to predominantly cytoplasmic expression in the basally located cornea epithelial cells of blast-exposed rabbits.

CONCLUSIONS

Primary blast exposure resulted in edema-related changes in the cornea manifested by the altered expression of the edema-regulating proteins AQP1 and AQP5 with blast overpressure-specific impulses. These findings support potential acute corneal injury mechanisms in which the altered regulation of water permeability is caused by primary blast exposure.

Biomechanical Impact of the Sclera on Corneal Deformation Response to an Air-Puff: A Finite-Element Study

Aim or Purpose: To describe the effect of varying scleral stiffness on the biomechanical deformation response of the cornea under air-puff loading via a finite-element (FE) model. Methods: A two-dimensional axisymmetric stationary FE model of the whole human eye was used to examine the effects varying scleral stiffness and intraocular pressure (IOP) on the maximum apical displacement of the cornea. The model was comprised of the cornea, sclera, vitreous, and surrounding air region. The velocity and pressure profiles of an air-puff from a dynamic Scheimpflug analyzer were replicated in the FE model, and the resultant profile was applied to deform the cornea in a multiphysics study (where the air-puff was first simulated before being applied to the corneal surface). IOP was simulated as a uniform pressure on the globe interior. The simulation results were compared to data from ex vivo scleral stiffening experiments with human donor globes. Results: The FE model predicted decreased maximum apical displacement with increased IOP and increased ratio of scleral-to-corneal Young's moduli. These predictions were in good agreement (within one standard deviation) with findings from ex vivo scleral stiffening experiments using human donor eyes. These findings demonstrate the importance of scleral material properties on the biomechanical deformation response of the cornea in air-puff induced deformation. Conclusion: The results of an air-puff induced deformation are often considered to be solely due to IOP and corneal properties. The current study showed that the stiffer the sclera, the greater will be the limitation on corneal deformation, separately from IOP. This may have important clinical implications to interpreting the response of the cornea under air-puff loading in pathologic conditions.

Pattern Electroretinography and Visual Evoked Potentials Provide Clinical Evidence of CNS Modulation of High- and Low-Contrast VEP Latency in Glaucoma

Purpose

Both pattern electroretinography (PERG) and visual evoked potentials (VEP) can be performed using low- (15%; Lc) and high- (85%; Hc) contrast gratings that may preferentially stimulate the magno- and parvocellular pathways. We observed that among glaucomatous patients showing only one VEP latency deficit per eye, there appeared to be a very strong tendency for an Hc delay in one eye and an Lc delay in the other.

Methods

Diopsys NOVA-LX system was used to measure VEP Hc and Lc latency among a clinical glaucoma population to find all individuals with either a single Hc or Lc latency abnormality in each eye (group 1), or with greater than 0 and less than 4 Hc or Lc VEP latency abnormalities in the two eyes (group 2) to determine whether a significant inverse correlation existed for these values in either group. Hc and Lc PERG data were also evaluated to assess associated retinal ganglion cell responses.

Results

A strong inverse correlation (P = 0.0000003) was observed between the Hc and Lc VEP latency values among the 64 eyes in group 1. Group 2 provided a comparable result (n = 143; 286 eyes; P = 0.0005). PERG (n = 81; 162 eyes) also showed strong bilateral symmetry for magnitude values (P < 0.0001 for both Lc and Hc in groups 1 and 2).

Conclusions

Bilateral retention of both low-resolution/high-speed and high-resolution/low-speed function may persist with both eyes open despite symmetrically pathologic retinal ganglion cell PERG waveform asynchrony for Hc and Lc stimuli in the paired eyes.

Translational Relevance

Clinical electrophysiology strongly suggests binocular compensation for dynamic dysfunction operates under central nervous system (CNS) control in glaucoma.

Tunable Surface Repellency Maintains Stemness and Redox Capacity of Human Mesenchymal Stem Cells

Human bone marrow derived mesenchymal stem cells (hMSCs) hold great promise for regenerative medicine due to their multipotent differentiation capacity and immunomodulatory capabilities. Substantial research has elucidated mechanisms by which extracellular cues regulate hMSC fate decisions, but considerably less work has addressed how material properties can be leveraged to maintain undifferentiated stem cells. Here, we show that synthetic culture substrates designed to exhibit moderate cell-repellency promote high stemness and low oxidative stress-two indicators of naïve, healthy stem cells-in commercial and patient-derived hMSCs. Furthermore, the material-mediated effect on cell behavior can be tuned by altering the molar percentage (mol %) and/or chain length of poly(ethylene glycol) (PEG), the repellant block linked to hydrophobic poly(ε-caprolactone) (PCL) in the copolymer backbone. Nano- and angstrom-scale characterization of the cell-material interface reveals that PEG interrupts the adhesive PCL domains in a chain-length-dependent manner; this prevents hMSCs from forming mature focal adhesions and subsequently promotes cell-cell adhesions that require connexin-43. This study is the first to demonstrate that intrinsic properties of synthetic materials can be tuned to regulate the stemness and redox capacity of hMSCs and provides new insight for designing highly scalable, programmable culture platforms for clinical translation.

The mechanical response of the porcine lens to a spinning test

The pig lens has been used as a model for presbyopia as pigs lack accommodative ability. Previous studies using microindentation have indicated that the shear modulus distribution is qualitatively similar to that of the aged human lens and that the lens does not alter its refractive power due to equatorial stretching. A lens spinning test was used to determine whether prior lens stiffness data obtained from a sectioned porcine lens were reliable and whether the testing conditions significantly influence the lens' mechanical properties. The elastic modulus distribution determined for fresh lenses closely matched that measured previously using a microindentation test. Confocal scanning laser microscopy was used to evaluate changes to the lens' structure arising from mechanical stress and following storage for up to one week.

Simulations of Porcine Eye Exposure to Primary Blast Insult

PURPOSE

A computational model of the porcine eye was developed to simulate primary blast exposure. This model facilitates understanding of blast-induced injury mechanisms.

METHODS

A computational model of the porcine eye was used to simulate the effects of primary blast loading for comparison with experimental findings from shock tube experiments. The eye model was exposed to overpressure-time histories measured during physical experiments. Deformations and mechanical stresses within various ocular tissues were then examined for correlation with pathological findings in the experiments.

RESULTS

Stresses and strains experienced in the eye during a primary blast event increase as the severity of the blast exposure increases. Peak stresses in the model occurred in locations in which damage was most often observed in the physical experiments.

CONCLUSIONS

Blast injuries to the anterior chamber may be due to inertial displacement of the lens and ciliary body while posterior damage may arise due to contrecoup interactions of the vitreous and retina. Correlation of modeling predictions with physical experiments lends confidence that the model accurately represents the conditions found in the physical experiments.

TRANSLATIONAL RELEVANCE

This computational model offers insights into the mechanisms of ocular injuries arising due to primary blast and may be used to simulate the effects of new protective eyewear designs.

Refined Frequency Doubling Perimetry Analysis Reaffirms Central Nervous System Control of Chronic Glaucomatous Neurodegeneration

PURPOSE

Refined analysis of frequency doubling perimetric data was performed to assess binocular visual field conservation in patients with comparable degrees of bilateral glaucomatous damage, to determine whether unilateral visual field loss is random, anatomically symmetric, or non-random in relation to the fellow eye.

METHODS

Case control study of 41 consecutive patients with bilaterally mild to severe glaucoma; each right eye visual field locus was paired with randomly-selected co-isopteric left eye loci, performing 690,000 (10,000 complete sets of 69 loci) such iterations per subject. The potential role of anatomic symmetry in bilateral visual field conservation was also assessed by pairing mirror-image loci of the right- and left-eye fields. The mean values of the random co-isopteric and the symmetric mirror pairings were compared with natural point-for-point pairings of the two eyes by paired t-test.

RESULTS

Mean unilateral Matrix threshold across the entire 30-degree visual field were 17.0 dB left and 18.4 dB right (average 17.7). The better of the naturally paired concomitant loci yielded binocular equivalent mean bilateral Matrix threshold of 20.9 dB, 1.6 dB higher than the population mean of the 690,000 coisopteric pairings (t = -10.4; P < 10^-12). Thus, a remarkable natural tendency for conservation of the binocular Matrix visual field was confirmed, far stronger than explicable by random chance. Symmetric pairings of precise mirror-image loci also produced values higher than random co-isopteric pairings (Δ 1.1 dB; t = -4.0; P = 0.0004).

CONCLUSIONS

Refined data analysis of paired Matrix visual fields confirms the existence of a natural optimization of binocular visual function in severe bilateral glaucoma via interlocking fields that could only be created by CNS involvement. The disparity of paired Matrix threshold values at mirror-image loci was also highly nonrandom and quantitatively inverse from the expected if anatomic symmetry factors were merely passively contributing systematically to the compensatory binocular Matrix effect.

TRANSLATIONAL RELEVANCE

The paired eyes and brain are reaffirmed to function as a unified system in the progressive age-related neurodegenerative condition chronic open angle glaucoma, maximizing the binocular visual field. Given the extensive homology of this disorder with other age-related neurodegenerations, it is reasonable to assume that the brain will similarly resist simultaneous bilateral loss of paired functional zones in both hemispheres in diseases like Alzheimer's and Parkinson's disease. Glaucomatous eyes at all stages of the disease appear to provide a highly accessible paired-organ study model for developing therapeutics to optimize conservation of function in neurodegenerative disorders.

Granulocyte colony-stimulating factor prevents loss of spermatogenesis after sterilizing busulfan chemotherapy

OBJECTIVE

To determine whether granulocyte colony-stimulating factor (G-CSF) could prevent loss of spermatogenesis induced by busulfan chemotherapy via protection of undifferentiated spermatogonia, which might serve as an adjuvant approach to preserving male fertility among cancer patients.

DESIGN

Laboratory animal study.

SETTING

University.

ANIMAL(S)

Laboratory mice.

INTERVENTION(S)

Five-week-old mice were treated with a sterilizing busulfan dose and with 7 days of G-CSF or vehicle treatment and evaluated 10 weeks later (experiment 1) or 24 hours after treatment (experiment 2).

MAIN OUTCOME MEASURE(S)

Experiment 1: testis weights, epididymal sperm counts, testis histology. Experiment 2: PLZF immunofluorescent costaining with apoptotic markers. Molecular analysis of G-CSF receptor expression in undifferentiated spermatogonia.

RESULT(S)

Ten weeks after treatment, busulfan-treated mice that also received treatment with G-CSF exhibited significantly better recovery of spermatogenesis and epididymal sperm counts than animals receiving busulfan alone. G-CSF led to increased numbers of PLZF+ spermatogonia 24 hours after treatment that was not accompanied by changes in apoptosis. To address the cellular target of G-CSF, mRNA for the G-CSF receptor, Csf3r, was found in adult mouse testes and cultured THY1+ (undifferentiated) spermatogonia, and cell-surface localized CSF3R was observed on 3% of cultured THY1+ spermatogonia.

CONCLUSION(S)

These results demonstrate that G-CSF protects spermatogenesis from gonadotoxic insult (busulfan) in rodents, and this may occur via direct action on CSF3R+ undifferentiated spermatogonia. G-CSF treatment might be an effective adjuvant therapy to preserve male fertility in cancer patients receiving sterilizing treatments.

Refined Data Analysis Provides Clinical Evidence for Central Nervous System Control of Chronic Glaucomatous Neurodegeneration

PURPOSE

Refined data analysis was performed to assess binocular visual field conservation in patients with bilateral glaucomatous damage to determine whether unilateral visual field loss is random, anatomically symmetric, or nonrandom in relation to the fellow eye.

METHODS

This was a case-control study of 47 consecutive patients with bilaterally severe glaucoma; each right eye visual field locus was paired with randomly selected coisopteric left eye loci, with 760,000 (10,000 complete sets of 76 loci) such iterations performed per subject. The potential role of anatomic symmetry in bilateral visual field conservation was also assessed by pairing mirror-image loci of the paired fields. The mean values of the random coisopteric and the symmetric mirror pairings were compared with natural point-for-point pairings of the two eyes by paired t-test.

RESULTS

Mean unilateral thresholds across the entire visual field were 18.9 dB left and 19.9 dB right (average 19.4), 4 dB lower than the better of the naturally paired concomitant loci of 23.4 dB (P < 10^-15). A remarkable natural tendency for conservation of the binocular visual field was confirmed, far stronger than explicable by random chance or anatomic symmetry (P < 0.0001), and reaffirmed by subsequent prospective simultaneous binocular visual field retesting of an arbitrary subset (n = 16) of the study population (P < 0.0001).

CONCLUSIONS

Refined data analysis of paired visual fields confirms the existence of a natural optimization of binocular visual function in severe bilateral glaucoma via interlocking fields that could be created only by central nervous system (CNS) involvement.

TRANSLATIONAL RELEVANCE

Integrated bilateral visual field analysis should better define actual visual disability and more accurately reflect the functional efficacy of current ocular and future CNS-oriented therapeutic approaches to the treatment of glaucoma. Glaucomatous eyes provide a highly accessible paired-organ study model for developing therapeutics to optimize conservation of function in neurodegenerative disorders.

Quantitative biometric phenotype analysis in mouse lenses

The disrupted morphology of lenses in mouse models for cataracts precludes accurate in vitro assessment of lens growth by weight. To overcome this limitation, we developed morphometric methods to assess defects in eye lens growth and shape in mice expressing the alphaA-crystallin R49C (alphaA-R49C) mutation. Our morphometric methods determine quantitative shape and dry weight of the whole lens from histological sections of the lens. This method was then used to quantitatively compare the biometric growth patterns of lenses of different genotypes of mice from birth to 12 months. The wild type dry lens weights determined using the morphometric method were comparable to previously reported weights. Next we applied the method to assessing the lenses of alphaA-R49C knock-in mice, which exhibit decreased alphaA-crystallin protein solubility, resulting in a variety of growth abnormalities including early cataract formation, decreased eye and lens size, failure to form the equatorial bow region, and continued lens cell death, sometimes resulting in the entire loss of the lens and eye. Our morphometric methods reproducibly quantified these defects by combining histology, microscopy, and image analysis. The volume measurement accurately represented the total growth of the lens, whereas the geometric shape of the lens more accurately quantified the differences between the growth of the mutant and wild-type lenses. These methods are robust tools for measuring dry lens weight and quantitatively comparing the growth of small lenses that are difficult to weigh accurately such as those from very young mice and mice with developmental lens defects.

In vivo lens deficiency of the R49C alphaA-crystallin mutant

The R49C mutation of alphaA-crystallin (alphaA-R49C) causes hereditary cataracts in humans; patients in a four-generation Caucasian family were found be heterozygous for this autosomal dominant mutation. We previously generated knock-in mouse models of this mutation and found that by 2 months of age, heterozygous mutant mice exhibited minor lens defects including reduced protein solubility, altered signaling in epithelial and fiber cells, and aberrant interactions between alphaA-crystallin and other lens proteins. In contrast, homozygous mutant alphaA-R49C knock-in mice displayed earlier and more extensive lens defects including small eyes and small lenses at birth, death of epithelial and fiber cells, and the formation of posterior, nuclear, and cortical cataracts in the first month of life. We have extended this study to now show that in alphaA-R49C homozygous mutant mice, epithelial cells failed to form normal equatorial bow regions and fiber cells continued to die as the mice aged, resulting in a complete loss of lenses and overall eye structure in mice older than 4 months. These results demonstrate that expression of the hereditary R49C mutant of alphaA-crystallin in vivo is sufficient to adversely affect lens growth, lens cell morphology, and eye function. The death of fiber cells caused by this mutation may ultimately lead to loss of retinal integrity and blindness.

A geometric model of ocular accommodation

An exoteric geometric mechanics model of ocular accommodation is detailed to elucidate the main ideas of various ongoing modeling efforts. The present study derives solutions for the stretched state of the ocular lens as it might appear during accommodation by using simple geometric arguments and a volume constraint, rather than the more mathematically intensive theory of elasticity. Results show that geometric shapes similar to the lens will deform in a similar fashion. This implies that, while the true lens geometry is somewhat more complex, it should also follow these qualitative behaviors.

A dynamic microindentation device with electrical contact detection

We developed a microindentation instrument that allows direct measurement of the point of contact for reasonably conductive samples. This is achieved in the absence of a contact load using a simple electrical circuit. Force is measured using an optical interrupter to measure the deflection of a cantilever beam. Displacement is achieved using a piezoelectric motor and is measured using an independent optical interrupter. Force and displacement measurements are accomplished in real time, allowing the specification of arbitrary waveforms. The instrument was rigorously validated by comparing mechanical property measurements from the indenter with results from traditional dynamic mechanical analysis. Details of the construction and feedback control schemes are given explicitly.

Comparison of the behavior of natural and refilled porcine lenses in a robotic lens stretcher

The mechanism by which the eye dynamically changes focal distance (accommodation), and the mechanism by which this ability is lost with age (presbyopia), are still contested. Due to inherent confounding factors in vivo, in vitro measurements have been undertaken using a robotic lens stretcher to examine these mechanisms as well as the efficacy of lens refilling - a proposed treatment for presbyopia. Dynamic forces, anterior and posterior curvatures, and lens thickness are all correlated for young natural and refilled porcine lenses. Comparisons are made to lenses refilled with a homogeneous polymer system. The amplitude of accommodation of the young porcine lens is very small such that it may be a suitable model for presbyopia. The behavior of refilled lenses was highly dependent on the refill volume. The volume could be tuned to maximize accommodative amplitude in the refilled lens.

Opposite effects of lithium on proximal and distal caspases of immature and mature primary neurons correlate with earlier paradoxical actions on viability

To provide an explanation for earlier paradoxical findings of lithium on survival of mature and immature neurons, this study monitors changes in cytosolic caspases in rat cerebellar granule cells (CGC) grown 2-7 days in vitro (DIV), or in murine E-17 cortical neurons. Data show Li+ protects mature 7-DIV CGC parallel to a decrease in proximal and distal caspases but increases levels for immature 2-DIV-CGC or E-17 cortical neurons. Caspases mirror viability based on morphological analyses (dye uptake, phase-contrast, DNA fragmentation), and suggest protection occurs by suppressing activation of a cascade resulting in distal effectors that destroy proteins essential for neuronal survival. Protection was dose-dependent with EC50 3.0 mM and extended to 64 h in K+-serum deprived apoptotic media. Neuronal extracts contain a spectrum of proximal (-2, -8, -9) and distal (-3, -6) caspases sensitive to Li+ on assay with preferred peptide substrates and by immunoblotting. The lack of direct effect on activated cytosols indicates Li+ acts upstream only on intact cells, at sites for recruitment of pivotal procaspases. Alterations of procaspase-9 p46 and membrane-bound cytochrome c (Apaf-1) point to interaction with an intrinsic Mt-mediated pathway as one of the targets. The opposite effects on caspases and viability of immature or embryological neurons point to existence of alternative pathways that alter during neurite outgrowth suggesting the use of Li+ as a probe to unravel events relevant to neurogenesis.

Three-dimensional echocardiography improves accuracy and compensates for sonographer inexperience in assessment of left ventricular ejection fraction

This study was performed to determine whether 3-dimensional echocardiography (3DE) with a magnetic tracking system for image plane localization, which unlike standard 2-dimensional echocardiography (2DE), does not require acquisition of specific image planes or "standard views" for quantitative measurement of left ventricular volume and ejection fraction (EF), could compensate for sonographer inexperience. Eight adults underwent magnetic resonance imaging (MRI) scanning; they also had 2DE and 3DE performed by 2 experienced and 3 novice sonographers. Data were analyzed by a single expert reader blinded to patient and sonographer identity. Linear regression of MRI EF (reference standard) against echocardiographic EF yielded the following results, where RD indicates the residual difference between measured MRI values and those predicted using echocardiographic results: expert 3DE: r = 0.97, RD = 2.4%, and r = 0.96, RD = 2.8%; novice 3DE: r = 0. 83, RD = 5.1%, to r = 0.95, RD = 4.8%; expert 2DE: r = 0.85, RD = 4. 8%, and r = 0.86, RD = 4.9%; and novice 2DE: r = 0.34, RD = 11.7%, to r = 0.69, RD = 6.6%. Comparison of error variances indicated that novices who used 3DE equaled the performance of experts who used 2DE, although experts were always more accurate than novices when both used the same echocardiographic method (3DE vs 3DE, 2DE vs 2DE). In a comparison of methods, 3DE was always superior to 2DE, regardless of sonographer experience. Three-dimensional echocardiography allows even novice sonographers to obtain diagnostic-quality data sets, which they were unable to accomplish with 2DE. These results suggest that scanning with 3DE, combined with remote expert interpretation, may be useful in providing echocardiographic services in regions where they are presently unavailable.

Phenylalanine kinetics are associated with tardive dyskinesia in men but not in women

RATIONALE

An association between tardive dyskinesia (TD) and severely impaired metabolism of the large neutral amino acid (LNAA), phenylalanine (Phe) was defined in a group of mentally retarded patients. Subsequently, an altered kinetics of Phe was associated with TD in men with schizophrenia based on plasma analyses subsequent to the ingestion of a protein meal.

METHODS

In the present study, a standardized oral challenge of pure Phe (100 mg/kg in 170 ml orange juice) was administered to psychiatric patients of both sexes (n = 312), with and without TD after an overnight fast. Plasma LNAA levels were assayed both fasting and 2 h subsequent to the ingestion of the challenge. The extent of the increase in plasma Phe levels 2 h following a standardized challenge is determined by the sum of the kinetic processes of plasma absorption, tissue distribution, metabolism and elimination.

RESULTS

The study hypothesis, that TD would be associated with significantly higher post-challenge plasma Phe indices of an absolute plasma Phe level and plasma Phe/LNAA ratio (a brain availability measure), was verified for the study men (n = 209), but not for the study women (n = 103).

CONCLUSIONS

The demonstrated altered kinetics of Phe in men with TD indicates a greater availability of Phe to the brain in these men. We suggest that the disorder may be related to the effects of this greater availability. Such effects could be the direct neurotoxic effects of Phe and its metabolites and/or the modulating effects of these compounds on the synthesis of the monoamine neurotransmitters. The fact that TD (Yes/No) group differences in post-challenge plasma Phe indices were not seen for the study women suggests the possibility of a sex difference in the biology of TD that we propose may be reflective of the young age of the study sample.

Glutamatergic receptor kinetics are not altered by perinatal exposure to aspartame

Observation of reduced levels of glutamic acid and aspartic acid in brain of weanling rats exposed perinatally to aspartame prompted a study of the effect of this food additive on glutamatergic receptor kinetics. Aspartame 500 mg/kg/day in drinking water was administered to Sprague-Dawley rats throughout gestation and lactation. Brain was excised from weanlings 20-22 days old, and kinetics of the N-methyl-D-aspartate receptor and total glutamatergic binding in cerebral cortex and hippocampus were found to be unaffected by perinatal exposure to high levels of aspartame. Glutamic acid was decreased in both brain regions studied, and aspartic acid was decreased in hippocampus following perinatal aspartame exposure. These changes were reversible when aspartame administration was terminated. It is concluded that perinatal exposure to high doses of aspartame does not alter glutamatergic neurotransmission in cerebral cortex or hippocampus from weanling rats.

The characterization of the metabolites of ranolazine in man by liquid chromatography mass spectrometry

The metabolism of ranolazine (RS-43285) or (+)N-(2,6-dimethylphenyl)-4[2-hydroxy-3-(2-methoxyphenoxy)-propyl]-1- piperazine acetamide dihydrochloride was investigated in man using plasma samples obtained from four different clinical studies. The metabolite profiles following single and multiple doses of 342 mg instant release (IR) ranolazine, following multiple doses of 1000 mg sustained release (SR) ranolazine and following dosing with both ranolazine (IR) and a potentially co-administered drug, diltiazem, were compared. Metabolism of ranolazine in man was shown by LC/MS analysis to be extensive with up to seven primary routes of metabolism identified. N-dealkylation by hydrolysis at the piperazine ring produced three metabolites whilst O-demethylation and O-dearylation at the methoxyphenoxy moiety produced a further two compounds. Additionally, hydrolysis of the amide group formed one other species. Oxygenation at various points in the molecule produced a further four metabolites. Direct conjugation of ranolazine with glucuronic acid and with an uncharacterized adduct were also identified as a route of elimination. Ten other biotransformation products were formed as a result of multiple metabolic steps. Conjugation was also associated with the desmethyl metabolite (glucuronide and unidentified conjugates) of hydroxylated ranolazine. In a previous publication (Journal of Chromatography, 1995, accepted for publication) semi-quantitative analyses of pooled plasma from the study where ranolazine was dosed at 1000 mg twice daily showed that of the twelve metabolites studied only four accounted for AUC's in excess of 10% of the ranolazine AUC.

Chronic nicotine administration increases binding of [3H]domperidone in rat nucleus accumbens

An apparent inverse relationship between smoking and Parkinson's disease prompted an investigation of the effect of chronic nicotine administration on dopaminergic and serotonergic receptors in rat brain. Nicotine, 0.8 mg/kg, was injected once daily, five times per week, for 6 weeks. In nucleus accumbens the Kd for [3H]domperidone was increased 2-4-fold, and the Bmax was increased 1.5-2-fold. No changes were observed in the binding of [3H]domperidone in caudate-putamen or in that of [3H]ketanserin in frontal cortex. It is concluded that chronic nicotine administration may have a suppressant effect on central nervous system release of dopamine that in pre-parkinsonian persons causes an aversion to the effects of smoking.

Intraneuronal dopaminergic action of cocaine and some of its metabolites and analogs

The present study investigated the actions of cocaine and some of its metabolites and analogs upon the synaptosomal (P2) synthesis and release of dopamine appearing from [14C]phenylalanine. Also examined was the influence of reserpine upon these actions of cocaine. The P2 preparations from the rat caudate nucleus were incubated with the drugs for [14C]phenylalanine and, after filtration, the particulates and medium fractions were analyzed for [14C]dopamine and [14C]phenylalanine. Labelled dopamine in the medium was taken as a measure of its release by any addition of drug. Cocaine, norcocaine and the synthetic cocaine analogs WIN 35428 and WIN 35-065(2) each stimulated both the total (medium plus particulates) formation and the release of dopamine, while benzoylecgonine and ecgonine were without effect. Reserpine inhibited the synthesis and enhanced the release of dopamine. An addition of reserpine blocked the stimulating effect of cocaine, norcocaine, WIN 35428 and WIN 35-065(2) on synthesis and furthermore, these drugs had, in the same experiments, inhibitory effects on the synthesis, additive to the reserpine-induced inhibition. Benzoylecgonine and ecgonine were only weakly inhibitory in the presence of reserpine. Stimulation, rather than additive inhibition, by cocaine was observed in the presence of exogenous dopamine, and amphetamine increased the synthesis in the presence of either reserpine or added dopamine. Pretreatment of rats with reserpine also blocked the stimulation of synthesis by cocaine and WIN 35428. The uptake of labelled substrate was not affected by addition of drug, or by the pretreatment.

Influence of chronic lithium administration on binding to benzodiazepine- and histamine H1-receptors in rat brain

In rat, chronic lithium treatment lowered the Kd of [3H]-mepyramine in midbrain, and reduced the Bmax in midbrain and pons-medulla. Binding of [3H]flunitrazepam in cerebellum and midbrain was not altered. The suggestion that some actions of lithium may occur by way of central nervous system receptors is further supported by these observations that lithium's effects on neurotransmitter systems are regional and specific.

Suppression of histamine-induced adrenocorticotropic hormone release by antihistamines and antidepressants

The antihistaminic activity of many antidepressant drugs is well documented in vitro but has not been investigated as thoroughly in vivo. In the course of an investigation of the roles of H1 and H2 receptors in histamine-induced adrenocorticotropic hormone (ACTH) release in rats, it was observed that several antidepressants were potent inhibitors of this response. Male Sprague-Dawley rats were injected with test drugs and then with histamine or histamine agonists. Serum ACTH concentrations were determined by radioimmunoassay. ACTH secretion was induced by both H1 and H2 receptor stimulation. Histamine-induced ACTH release was markedly attenuated by several H1 antihistamines, whereas the H2 antagonists were not as effective. The antidepressants imipramine, doxepin, mianserin, desipramine and amitriptyline suppressed histamine-induced ACTH release. However, iprindole and the antianxiety agent diazepam were without effect. ACTH release induced by histamine agonists was also diminished by pretreatment with some of these blocking agents.

Effects of various S-adenosylmethionine preparations on histamine methylation in vitro and in vivo

To test possible enhancement of in vivo methylation of histamine, mice were injected with S-adenosylmethionine (SAM) of approximately 96% purity. Instead of the expected enhancement, very strong inhibition of methylation was observed. Tests indicated that S-adenosylhomocysteine (SAH) probably was not the inhibitor. Pure SAM, from another source, showed no inhibition of methylation in rats and guinea pigs, and only slight inhibition in mice. Pure SAM was much more effective than the 96% SAM for histamine methylation in vitro. It seems either that injected SAM cannot enter cells containing the histamine methylating enzyme (HME), or that the endogenous supply of SAM is optimal. The inhibitor may be structurally related to SAM, possibly a by-product of SAM synthesis. As it is very effective even in the presence of large amounts of SAM, in pure form it would probably be the most potent inhibitor of histamine methylation available.

Effect of histamine methylation inhibitors on entry of 14C-histamine into brain

Pretreatment of mice, rats and guinea pigs with inhibitors of histamine methylation, followed by systemic injection of 14C-histamine, results in a significant increase in brain 14C-histamine relative to controls. It is suggested that the histamine methylating enzyme participates in the blood-brain barrier to histamine.