Optical Properties Of Lenses Research Articles

Comparison Between the Properties of Three New Designs of Pinhole Magnetic Lens

Three different new designs of an objective pinhole lens were compared. Their magnetic and optical properties were studied using Finite Element Method for Calculating Magnetic Field Distribution (FEM-CMFD) and Magnetic Electron Lens Optical Properties (MELOP) software. The focal length (fo), spherical aberration (Cs), chromatic aberration (Cc), and the resolving power (δ) of each lens were compared at a range of relatively corrected acceleration voltages (Vr = 100 V-100 kV) and a constant excitation of (NI = 5280 A-t (where A represents Ampere and t represents turn)) and current density (2 A/mm2) to find the best design. The L1 lens is similar to the Gemini lens. L2 and L3 are the traditional pinhole lens shape. The L1 lens gave the best results in terms of optical and magnetic properties as its optical properties at medium and low acceleration voltages. L2 and L3 Lenses had almost identical magnetic properties, but the difference was apparent in optical properties.

The 18th amino acid glycine plays an essential role in maintaining the structural stabilities of γS-crystallin linking with congenital cataract

γS-crystallin is particularly rich in the embryonic nuclear region and is crucial to the maintenance of lens transparency and optical properties. Gene mutations in crystallin are the main factors leading to congenital hereditary cataracts, which are a major cause of visual impairment in children. Some mutations located in the 18th amino acid glycine of γS-crystallin were reported to be linking with congenital cataracts. However, the pathogenic mechanism has not been elucidated. Interestingly, we previously identified a novel variant of γS-crystallin (c.53G > A; p. G18D) with progressive cortical and sutural congenital cataracts in one Chinese family. In this study, we purified the γS-crystallin wildtype and mutant proteins to investigate the effects of the G18D mutation on the structural stability of γS-crystallin. The results showed that there were tertiary structural differences between the wild-type γS-crystallin and the G18D variant. The mutation significantly impaired the stability of γS-crystallin under environmental stress and promoted aggregation. Furthermore, molecular dynamics (MD) simulations showed that the mutation altered H-bonding and surface electrostatic potential. Significantly decreased stability along with an increased tendency to aggregate under environmental stress may be the major pathogenic factors for cataracts induced by the G18D mutation.

Evaluation of cataract formation in fish exposed to environmental radiation at Chernobyl and Fukushima

Recent studies apparently finding deleterious effects of radiation exposure on cataract formation in birds and voles living near Chernobyl represent a major challenge to current radiation protection regulations. This study conducted an integrated assessment of radiation exposure on cataractogenesis using the most advanced technologies available to assess the cataract status of lenses extracted from fish caught at both Chernobyl in Ukraine and Fukushima in Japan. It was hypothesised that these novel data would reveal positive correlations between radiation dose and early indicators of cataract formation.The structure, function and optical properties of lenses were analysed from atomic to millimetre length scales. We measured the short-range order of the lens crystallin proteins using Small Angle X-Ray Scattering (SAXS) at both the SPring-8 and DIAMOND synchrotrons, the profile of the graded refractive index generated by these proteins, the epithelial cell density and organisation and finally the focal length of each lens.The results showed no evidence of a difference between the focal length, the epithelial cell densities, the refractive indices, the interference functions and the short-range order of crystallin proteins (X-ray diffraction patterns) in lens from fish exposed to different radiation doses. It could be argued that animals in the natural environment which developed cataract would be more likely, for example, to suffer predation leading to survivor bias. But the cross-length scale study presented here, by evaluating small scale molecular and cellular changes in the lens (pre-cataract formation) significantly mitigates against this issue.

Surgeon's Eyes on the Relevant Surgical Target.

The resolution of the naked eye has been a challenge for the neurosurgical endeavor since the very first attempts of cranial surgery, and advances have been achieved over the centuries, driven by a synergism between the application of emerging technology into the surgical environment and the expansion of the capabilities of neurosurgery. The understanding of the principles of the optical properties of lenses by Abbè (1840-1905) led to the introduction of loupes in the surgical practice, increasing the visual performance during macroscopic procedures. Modern neurosurgery began with the possibility of illumination and magnification of the surgical field as provided by the microscope. Pioneering contributions from Donaghy and Yasargil opened the way to the era of minimalism with reduction of operative corridors and surgical trauma through the adoption of the microsurgical technique. Almost at the same time, engineering mirabilia of Hopkins in terms of optics and lenses allowed for introduction of rigid and flexible endoscopes as a viable tool in neurosurgery. Nowadays, neurosurgeons are aware of and confident using effective and modern tools of visualization in their armamentarium. Herein we present a cogent review of the evolution of visualization tools in neurosurgery, with a special glimpse into the current development and future achievements.

Effect of displacement in object plane on reconstructed image in lens-based digital holography

Optical properties of lenses play significant role in digital holographic setups to increase their applications in several fields of imaging and non-destructive testing. In present work, we investigate the effect of introduction of lenses on quality of reconstructed images when they are placed between the object and the image sensor in digital holography. We define a range of propagation distance suitable for recording digital holograms using different off-axis digital holographic setups. The reconstruction results of conventional off-axis digital holographic setup are taken as reference to compare them with lens-based digital holographic setups. Three different digital holographic setups are realised using lenses i.e. concave lens-based setup, convex lens-based setup, and combined concave and convex lenses-based setup. The quality of the reconstructed image is measured by calculating their structural similarity index measure (SSIM) values. These values compare the reconstructed image obtained in the experiment with a reference image of the object obtained through its computer generated hologram (CGH). Performance of these digital holographic setups is compared on the basis of SSIM values of reconstructed images calculated for different separation between object to sensor. On the basis of SSIM values, a range of distances suitable for recording digital holograms for each setup is obtained as 220 mm to 400 mm for the concave lens-based setup, 560 mm to 800 mm for convex lens-based setup, and 220 mm to 600 mm for the concave-convex lens-based setup using concave lens of 50 mm focal length and a convex lens of 80 mm focal length in the experiments.

Relationship of the cornea and globe dimensions to the changes in adult human crystalline lens diameter, thickness and power with age

It is well known that human crystalline lens shape, dimensions and optical properties change throughout life and influence whole eye refraction. However, it is not clear if lens properties are associated with other ocular parameters. The purpose of the present study was to investigate the relationship of corneal and external globe dimensions with adult lens diameter (LD), lens thickness (LT) and lens power (LP) in order to determine if external factors influence lens properties. Postmortem human eyes (n = 66, age = 20–78 years) were obtained from the Ramayamma International Eye Bank, Hyderabad, India. Globe antero-posterior length (GAPL) and mean (average of horizontal and vertical) diameters of cornea (MCD) and globe (MGD) were measured using digital calipers. Eyes were dissected to produce ocular structures that contain the lens maintained in its accommodating framework, including intact zonules, ciliary body and sections of sclera. Specimens were mounted in a mechanical lens stretching system. LD, LT and LP were measured using high magnification retro-illumination photography, slit illumination photography and Scheiner principle-based optical system respectively in the unstretched (accommodated) state. Relationships between external globe and corneal dimensions and LD, LT or LP were assessed by multiple regression analysis. Age (0.012 ± 0.003 mm/year; p<0.001) and GAPL (0.185 ± 0.045 mm/mm; p<0.001) were significant (p<0.0001) predictors of LD. After adjusting for age-related increases, LD appears to be positively correlated with GAPL. Age (0.010 ± 0.004 mm/year; p = 0.009) and GAPL (−0.143 ± 0.060 mm/mm; p = 0.02) were significant (p = 0.001) predictors of LT. After adjusting for the age-related increase, LT appears to be negatively correlated with GAPL. Only age was a significant predictor of LP (−0.26 ± 0.04 D/year; p<0.001). The results suggest that, apart from aging, lens diameter and thickness are dependent on the anteroposterior length of the eye globe. Lens power is not influenced by globe dimensions.

Simple program for computing objective optical properties of magnetic lenses

The paper describes the basic features of a new program denoted Magnetic Electron Lens Optical Properties (MELOP), primarily intended for providing free and simple way to calculate the objective focal properties of rotationally-symmetric electron magnetic lenses with the presence of its axial magnetic field distribution. The calculation is done by solving the paraxial ray equation using the fourth-order Runge-Kutta formula. For specific beam voltage, the program computes the excitation parameter, the object or image plane, the objective principal plane, the objective focal length, the objective magnification, the spherical aberration coefficient, the chromatic aberration coefficient and the magnetic flux density at the object or image plane. These parameters are solved for zero, low, high or infinite magnification condition. The program can handle instantaneously plotting the variations of the calculated parameters relatively. In addition to that, the data can be transferred to xlsx or txt file format.

Crystalline lens gradient refractive index distribution in the guinea pig.

The crystalline lens undergoes morphological and functional changes with age and may also play a role in eye emmetropisation. Both the geometry and the gradient index of refraction (GRIN) distribution contribute to the lens optical properties. We studied the lens GRIN in the guinea pig, a common animal model to study myopia. Lenses were extracted from guinea pigs (Cavia porcellus) at 18days of age (n=4, three monolaterally treated with negative lenses and one untreated) and 39days of age (n=4, all untreated). Treated eyes were myopic (-2.07D on average) and untreated eyes hyperopic (+3.3D), as revealed using streak retinoscopy in the live and cyclopeged animals. A custom 3D spectral domain optical coherence tomography (OCT) system(λ=840nm, Δλ=50nm) was used to image the enucleated crystalline lens at two orientations. Custom algorithms were used to estimate the lens shape and GRIN was modelled with four variables that were reconstructed using the OCT data and a minimisation algorithm. Ray tracing was used to calculate the optical power and spherical aberration assuming a homogeneous refractive index or the estimated GRIN. Guinea pig lenses exhibited nearly parabolic GRIN profiles. When comparing the two age groups (18- and 39day-old) there was a significant increase in the central thickness (from 3.61 to 3.74mm), and in the refractive index of the surface (from 1.362 to 1.366) and the nucleus (from 1.443 to 1.454). The presence of GRIN shifted the spherical aberration (-4.1µm on average) of the lens towards negative values. The guinea pig lens exhibits a GRIN profile with surface and nucleus refractive indices that increase slightly during the first days of life. GRIN plays a major role in the lens optical properties and should be incorporated into computational guinea pig eye models to study emmetropisation, myopia development and ageing.

This Issue of Acta

This Issue of Acta

Long-term prevention of capsular opacification after lens-refilling surgery in a rabbit model.

PurposeTo reduce capsular opacification by a peri‐surgical treatment of the lens capsule with drugs in an in vivo rabbit model. Lens‐refilling surgery is a potential therapeutic intervention to treat patients with a cataract lens. The lens material is replaced with an injectable (bio)polymer that retains the natural mechanical and optical lens properties, therewith allowing accommodation. The occurrence of capsular opacification mediated by lens epithelial cells negatively affects accommodation and vision and should be avoided in this lens restoration approach.MethodsAn in vivo rabbit animal model was used with lens replacement with a silicone‐based gel‐like polymer and concurrent treatment of the lens epithelium with drugs. A case‐study approach was applied as both drug combinations and implantation times were varied. The following drugs were investigated for their potential to prevent capsular opacification long‐term: actinomycin D, methotrexate, paclitaxel and Tween‐20. All were administered in a hyaluronic acid vehicle. The rabbits were clinically followed for periods up to 4 years postimplantation. Eyes, corneas and lenses were analysed post‐mortem using MRI and confocal microscopy.ResultsTreatment combinations containing actinomycin D generally led to the least appearance of capsular fibrosis. The use of Tween‐20 or paclitaxel without actinomycin D resulted in much earlier and pronounced fibrotic responses. The aspect of capsular opacification was highly variable in individual animals. Application of the drugs in a hyaluronic acid vehicle appeared to be a safe method that spared the corneal endothelium.ConclusionThe feasibility of long‐term prevention of fibrosis over a period of more than 4 years has been demonstrated in lens refilling in the rabbit model.

Optimization of Light Transmission through an Excitation-scan Hyperspectral Mirror Array System.

Hyperspectral imaging has numerous applications in a range of fields for target detection. While its original applications were in remote sensing, new uses include analyzing food quality, agriculture and medicine, Hyperspectral imaging has shown utility in fluorescence microscopy for detecting signatures from many fluorescent molecules, but acquisition speeds have been slow due to the need to acquire many spectral bands and the light losses associated with spectral filtering. Therefore, a novel confocal microscope, the 5-Dimensional Rapid Hyperspectral Imaging Platform (RHIP-5D) was designed and is undergoing testing to overcome acquisition speed and sensitivity limitations. The current design utilizes light-emitting diodes (LEDs) and a multifaceted mirror array to combine light sources into a liquid light guide. Initial tests demonstrated feasibility and we are now working on determining the ideal location of the liquid light guide, LEDs, lenses and mirror array to optimize optical transmission. A computational model was constructed using Monte Carlo optical ray tracing in TracePro software (Lambda Research Corp.). LED sources were simulated by importing irradiance properties from the manufacturers' specifications. Optical properties of lenses were modeled using lens files available from the manufacturer. Analysis of the model includes geometry and parametric optimization, assessing lens power, mirror angles and location of optical elements. Initial results show an increase of transmission is possible by up to 20%. Future work will involve evaluating the position of the liquid light guide as well as analyzing lens configurations to further increase optical transmission.

고분자막과 다층구조를 이용한 가변렌즈기반 광학 줌 시스템

We have developed an optical zoom system based on tunable lens with polymer membrane and multilayered structure. The presented system employed two tunable lenses and two doublet lenses as the main refractive units. Each tunable lens had a delicately designed, solid-liquid mixed structure with multiple internal slim holes, which helped to improve the lens optical properties and stability against gravity. The optical structure and regulation principle of the zoom system is presented, as well as the detailed fabrication process of the tunable lens. Under different displacement loads, the lens deformation properties, and the adjustment ability and imaging characteristics of the zoom system were measured and analyzed. Besides, the spot diagram, field curvature and distortion of the system were simulated using the Zemax software. The magnification of the designed system could be regulated from 0.2X to 4.3X flexibly depending on the focal variation of each tunable lens.

Transgenic zebrafish models reveal distinct molecular mechanisms for cataract-linked αA-crystallin mutants

Mutations in the small heat shock proteins α-crystallins have been linked to autosomal dominant cataracts in humans. Extensive studies in vitro have revealed a spectrum of alterations to the structure and function of these proteins including shifts in the size of the oligomer, modulation of subunit exchange and modification of their affinity to client proteins. Although mouse models of these mutants were instrumental in identifying changes in cellular proliferation and lens development, a direct comparative analysis of their effects on lens proteostasis has not been performed. Here, we have transgenically expressed cataract-linked mutants of αA- and αB-crystallin in the zebrafish lens to dissect the underlying molecular changes that contribute to the loss of lens optical properties. Zebrafish lines expressing these mutants displayed a range of morphological lens defects. Phenotype penetrance and severity were dependent on the mutation even in fish lines lacking endogenous α-crystallin. The mechanistic origins of these differences were investigated by the transgenic co-expression of a destabilized human γD-crystallin mutant. We found that the R49C but not the R116C mutant of αA-crystallin drove aggregation of γD-crystallin, although both mutants have similar affinity to client proteins in vitro. Our working model attributes these differences to the propensity of R49C, located in the buried N-terminal domain of αA-crystallin, to disulfide crosslinking as previously demonstrated in vitro. Our findings complement and extend previous work in mouse models and emphasize the need of investigating chaperone/client protein interactions in appropriate cellular context.

Congenital microcornea-cataract syndrome-causing mutation X253R increases βB1-crystallin hydrophobicity to promote aggregate formation

The high solubility and lifelong stability of crystallins are crucial to the maintenance of lens transparency and optical properties. Numerous crystallin mutations have been linked to congenital cataract, which is one of the leading causes of newborn blindness. Besides cataract, several crystallin mutations have also been linked to syndromes such as congenital microcornea-cataract syndrome (CMCC). However, the molecular mechanism of CMCC caused by crystallin mutations remains elusive. In the present study, we investigated the mechanism of CMCC caused by the X253R mutation in βB1-crystallin. The exogenously expressed X253R proteins were prone to form p62-negative aggregates in HeLa cells, strongly inhibited cell proliferation and induced cell apoptosis. The intracellular X253R aggregates could be successfully redissolved by lanosterol but not cholesterol. The extra 26 residues at the C-terminus of βB1-crystallin introduced by the X253R mutation had little impact on βB1-crystallin structure and stability, but increased βB1-crystallin hydrophobicity and decreased its solubility. Interestingly, the X253R mutant fully abolished the aggregatory propensity of βB1- and βA3/βB1-crystallins at high temperatures, suggesting that X253R was an aggregation-inhibition mutation of β-crystallin homomers and heteromers in dilute solutions. Our results suggest that an increase in hydrophobicity and a decrease in solubility might be responsible for cataractogenesis induced by the X253R mutation, while the cytotoxic effect of X253R aggregates might contribute to the defects in ocular development. Our results also highlight that, at least in some cases, the aggregatory propensity in dilute solutions could not fully mimic the behaviours of mutated proteins in the crowded cytoplasm of the cells.

Time Series Artificial Neural Network Approach for Prediction of Optical Lens Properties

Well-designed electrostatic cylindrical lenses are commonly used to control charged particles in atomic and molecular physics instruments such as electron guns and electron microscopes. The most commonly used of these, three-element electrostatic lenses are capable of keeping magnification constant for definite image position. The correct determination of focal and aberration characteristics of these lenses is very important for experimental studies. In this study, motions of electrons in three-element electrostatic cylindrical lenses have been investigated with nonlinear autoregressive exogenous based time series artificial neural network technique. The spherical and chromatic aberrations which aect the beam are also predicted with time series artificial neural network technique. This method is a mathematical model that emulates the biological neural networks. The basic working principle of time series artificial neural network technique is training of network with the known data and then prediction of the unknown data. Simulation results from SIMION 8.1 ray-tracing program are used as training and test data set. According to the results obtained from time series artificial neural network technique technique, a considerably agreement is found between simulation and artificial neural network technique prediction results. The study shows that such an artificial neural network model which has time advantage can be applicable to various electron and ion beam apparatus.

Organic-inorganic-hybrid-polymer microlens arrays with tailored optical characteristics and multi-focal properties.

Plano-convex microlens arrays of organic-inorganic polymers with tailored optical properties are presented. The fine-tuning of each microlens within an array is achieved by confining inkjet printed drops of the polymeric ink onto pre-patterned substrates. The lens optical properties are thus freely specified, and high numerical apertures from 0.45 to 0.9 and focal lengths between 10 μm and 100 μm are demonstrated, confirming theoretical predictions. Combining nanoimprint lithography approaches and inkjet printing enables using the same material for the microlenses and their substrates, improving the optical performances. Microlens arrays with desired specifications are printed reaching yields up to 100% and high lens reproducibility with standard deviations of the apparent contact angle under 1° and of the numerical apertures and focal lengths under 6%. Microlens arrays involving lenses with different characteristics, e.g. multi focal length, and thus focal planes separated by only few microns are printed with the same reproducibility.

Species-Specific Structural and Functional Divergence of α-Crystallins: Zebrafish αBa- and Rodent αA(ins)-Crystallin Encode Activated Chaperones.

In addition to contributing to lens optical properties, the α-crystallins are small heat shock proteins that possess chaperone activity and are predicted to bind and sequester destabilized proteins to delay cataract formation. The current model of α-crystallin chaperone mechanism envisions a transition from the native oligomer to an activated form that has higher affinity to non-native states of the substrate. Previous studies have suggested that this oligomeric plasticity is encoded in the primary sequence and controls access to high affinity binding sites within the N-terminal domain. Here, we further examined the role of sequence variation in the context of species-specific α-crystallins from rat and zebrafish. Alternative splicing of the αA gene in rodents produces αA(ins), which is distinguished by a longer N-terminal domain. The zebrafish genome includes duplicate αB-crystallin genes, αBa and αBb, which display divergent primary sequence and tissue expression patterns. Equilibrium binding experiments were employed to quantitatively define chaperone interactions with a destabilized model substrate, T4 lysozyme. In combination with multiangle light scattering, we show that rat αA(ins) and zebrafish α-crystallins display distinct global structural properties and chaperone activities. Notably, we find that αA(ins) and αBa demonstrate substantially enhanced chaperone function relative to other α-crystallins, binding the same substrate more than 2 orders of magnitude higher affinity and mimicking the activity of fully activated mammalian small heat shock proteins. These results emphasize the role of sequence divergence as an evolutionary strategy to tune chaperone function to the requirements of the tissues and organisms in which they are expressed.

A conserved role of αA-crystallin in the development of the zebrafish embryonic lens

αA- and αB-crystallins are small heat shock proteins that bind thermodynamically destabilized proteins thereby inhibiting their aggregation. Highly expressed in the mammalian lens, the α-crystallins have been postulated to play a critical role in the maintenance of lens optical properties by sequestering age-damaged proteins prone to aggregation as well as through a multitude of roles in lens epithelial cells. Here, we have examined the role of α-crystallins in the development of the vertebrate zebrafish lens. For this purpose, we have carried out morpholino-mediated knockdown of αA-, αBa- and αBb-crystallin and characterized the gross morphology of the lens. We observed lens abnormalities, including increased reflectance intensity, as a consequence of the interference with expression of these proteins. These abnormalities were less frequent in transgenic zebrafish embryos expressing rat αA-crystallin suggesting a specific role of α-crystallins in embryonic lens development. To extend and confirm these findings, we generated an αA-crystallin knockout zebrafish line. A more consistent and severe lens phenotype was evident in maternal/zygotic αA-crystallin mutants compared to those observed by morpholino knockdown. The penetrance of the lens phenotype was reduced by transgenic expression of rat αA-crystallin and its severity was attenuated by maternal αA-crystallin expression. These findings demonstrate that the role of α-crystallins in lens development is conserved from mammals to zebrafish and set the stage for using the embryonic lens as a model system to test mechanistic aspects of α-crystallin chaperone activity and to develop strategies to fine-tune protein–protein interactions in aging and cataracts.

English

We present in this paper the quantification of the geometrical features of the anterior segment of the eye using Anterior Segment Optical Coherence Tomography (AS-OCT). This quantification was achieved by following our own developed methodology including the device development and their distortion calibration (Fan and refraction) for 3-D imaging, and automatic analysis tools as well. The stastistical comparison of the corrected topographies of the anterior cornea with topographies from state-of-the art clinical topography systems represents a valuable contribution toward the development All-OCT-based topographic systems. In addition, we first reported topographies of the crystalline lens in vivo, which is a promising tool to investigate the lens optical properties, the contribution of the lens to the overall retinal image quality, and understanding the change of the physical properties of the lens with accommodation and aging. Furthermore, our quantitative AS-OCT allowed the analysis of the keratoconic cornea and the changes produced by Intra Corneal Ring Segment (ICRS) treatment, as well as monitoring of the ICRS 3-D location. Finally, OCT-based biometry we present in this paper is a promising tool to investigate the changes after cataract surgery; the contribution of the (Intra Ocular Lens) IOL location and tilt to the overall retinal image quality, and in the design of new IOLs.

Determination of injection molding process windows for optical lenses using response surface methodology.

This study focuses on injection molding process window determination for obtaining optimal imaging optical properties, astigmatism, coma, and spherical aberration using plastic lenses. The Taguchi experimental method was first used to identify the optimized combination of parameters and significant factors affecting the imaging optical properties of the lens. Full factorial experiments were then implemented based on the significant factors to build the response surface models. The injection molding process windows for lenses with optimized optical properties were determined based on the surface models, and confirmation experiments were performed to verify their validity. The results indicated that the significant factors affecting the optical properties of lenses are mold temperature, melt temperature, and cooling time. According to experimental data for the significant factors, the oblique ovals for different optical properties on the injection molding process windows based on melt temperature and cooling time can be obtained using the curve fitting approach. The confirmation experiments revealed that the average errors for astigmatism, coma, and spherical aberration are 3.44%, 5.62%, and 5.69%, respectively. The results indicated that the process windows proposed are highly reliable.