Natural Lens Research Articles

Traveling ionospheric disturbances as huge natural lenses: Solar radio emission focusing effect

AbstractWe present an in‐depth study into spectral perturbations appearing in solar dynamic spectra and being manifestations of the focusing effect of low‐frequency solar emission by the Earth's ionosphere. Such perturbations are considered to be the result of radio waves focusing by medium scale traveling ionospheric disturbances (MSTIDs). Using the Nançay Decametric Array (NDA) data set, we have conducted a statistical analysis of the spectral structures in solar dynamic spectra within 10–80 MHz. We have detected the spectral structures in the NDA spectral data for 129 observation days from 1999 to 2015. On spectrograms they appear as intensity variations different from well‐known solar radio bursts. The sharp edges with enhanced intensity are distinctive characteristics of the structures for most events. Due to this spectral feature, they are termed as Spectral Caustics (SCs). We have classified the SCs observed by the NDA as several types, based on their spectral morphology, namely: inverted V like, V like, X like, fiber like, and fringe like. We have found that the rate of occurrence of SCs in dynamic spectra depends on the phase of the solar cycle. About 81% of all days with detected SCs fall on active phases of solar cycles 23 and 24 (48% and 33%, respectively). We have also established the seasonal dependence in occurrence of the SCs. It was found that about 95% of days with SCs belong to autumn‐winter months, whereas only near 5% of days with SCs belong to spring‐summer months. This is well correlated with the reported dependence in MSTID occurrence rate.

An attempt at natural lens regeneration in congenital cataract surgery

Despite recent advances, successful rehabilitation of children with congenital cataracts is hampered by a range of unresolved issues. The purpose of this study was to aquire personal assessment of the successful experience of Lin on 24 eyes that underwent a modified aspiration procedure followed by natural lens regeneration.

Ecological restoration should be redefined for the twenty-first century.

Forty years ago, ecological restoration was conceptualized through a natural science lens. Today, ecological restoration has evolved into a social and scientific concept. The duality of ecological restoration is acknowledged in guidance documents on the subject but is not apparent in its definition. Current definitions reflect our views about what ecological restoration does but not why we do it. This viewpoint does not give appropriate credit to contributions from social sciences, nor does it provide compelling goals for people with different motivating rationales to engage in or support restoration. In this study, I give a concise history of the conceptualization and definition of ecological restoration, and I propose an alternative definition and corresponding viewpoint on restoration goal‐setting to meet twenty‐first century scientific and public inquiry.

Multiple issues in multifocal intraocular lens

The occurrence of multifocal intraocular lens (MIOL) is known as an important period in the development of cataract surgery, which can provide a simultaneous vision without the use of spectacles or contact lenses. However, in the current stage, MIOL implantation may also lead to decreased visual acuity and increased risk of photic phenomena, thus in some instance a second procedure to exchange the MIOL is necessary. Optimizing visual outcomes of MIOL implantation and controlling adverse effects has become the focus for ophthalmologists. In the future, a more remarkable, flexible and high cost-effective intraocular lens (IOL), which can mimic human natural crystalline lens, should emerge. (Chin J Ophthalmol, 2017, 53: 244-248).

Missed retinal breaks in rhegmatogenous retinal detachment.

To evaluate the causes and associations of missed retinal breaks (MRBs) and posterior vitreous detachment (PVD) in patients with rhegmatogenous retinal detachment (RRD). Case sheets of patients undergoing vitreo retinal surgery for RRD at a tertiary eye care centre were evaluated retrospectively. Out of the 378 records screened, 253 were included for analysis of MRBs and 191 patients were included for analysis of PVD, depending on the inclusion criteria. Features of RRD and retinal breaks noted on examination were compared to the status of MRBs and PVD detected during surgery for possible associations. Overall, 27% patients had MRBs. Retinal holes were commonly missed in patients with lattice degeneration while missed retinal tears were associated with presence of complete PVD. Patients operated for cataract surgery were significantly associated with MRBs (P=0.033) with the odds of missing a retinal break being 1.91 as compared to patients with natural lens. Advanced proliferative vitreo retinopathy (PVR) and retinal bullae were the most common reasons for missing a retinal break during examination. PVD was present in 52% of the cases and was wrongly assessed in 16%. Retinal bullae, pseudophakia/aphakia, myopia, and horse shoe retinal tears were strongly associated with presence of PVD. Traumatic RRDs were rarely associated with PVD. Pseudophakic patients, and patients with retinal bullae or advanced PVR should be carefully screened for MRBs. Though Weiss ring is a good indicator of PVD, it may still be over diagnosed in some cases. PVD is associated with retinal bullae and pseudophakia, and inversely with traumatic RRD.

Off-axis astigmatism in the isolated chicken crystalline lens

The chicken eye was previously found to have little off-axis astigmatism which is not explained by its special corneal shape but rather by the optical properties of the crystalline lens. To learn more about lens design, we studied off-axis astigmatism in the chicken lens in situ and compared it to a glass lens of similar power but with homogenous refractive index. After euthanasia, enucleated eye balls were cut in the equatorial plane right behind the scleral ossicles. The anterior segment was placed in a water-filled chamber. Several thin laser beams were projected in two perpendicular meridians through the lens under various eccentricities and the focal lengths were determined. Off-axis astigmatism across the horizontal visual field was determined as the differences in power in the two meridians. The same procedure was used for the glass lens. On-axis, the chicken crystalline lens had slightly more power in the vertical than in the horizontal meridian (−2.8±0.7D (SEM)). Astigmatism flipped sign and increased with eccentricity to reach +6.1±2.1D (SEM) at 33.5deg off-axis, as expected from off-axis astigmatism. Even though this value appears high, it was still 2.5 times lower than in the glass lens. A ZEMAX model of a lens with a homogeneous index and with surface profiles taken of the natural chicken lens revealed even higher levels of off-axis astigmatism. Obviously, the natural chicken lens displays much less off-axis astigmatism than a glass lens with similar power. Since its shape does not explain the low off-axis astigmatism, it must be due to a refined internal refractive index structure.

Оценка параметров переднего отрезка глаза методом оптической когерентной томографии у пациентов с высокой миопией, корригированной факичной интраокулярной линзой

Purpose . To assess anatomic topographic parameters of the anterior chamber of the eye in patients with high myopia corrected with the angle-supported phakic intraocular lens (PIOL) of the Cachet design using the anterior segment optical coherence tomography (AS-OCT). Material and methods . Seventeen highly myopic patients (31 eyes) corrected with angle-supported PIOL Cachet (Alcon) were examined in the period from September 2010 to December 2013. Mean age of the patients was 25.8±4.6 years. Mean spherical equivalent was -12.38±3.64D. All patients underwent comprehensive preand post-operative examinations, including the AS-OCT (Visante OCT, Carl Zeiss Meditec AG). Preoperatively the horizontal and vertical anterior chamber diameters (Angle-toAngle, ATA) were measured and the anterior chamber depth (from corneal epithelium and endothelium) using the AS-OCT. Also 3-12 months postoperatively the following parameters were assessed: «PIOL – corneal endothelium» (central), «PIOL – natural lens» (central) and «PIOL edge – corneal endothelium» (temporal and nasal). Results . The mean preoperative horizontal and vertical anterior chamber diameters were 12.07±0.38mm and 12.46±0.44mm, respectively (P<001). The mean preoperative anterior chamber depth values from corneal epithelium and corneal endothelium were 3.88±0.31mm and 3.36±0.33mm, respectively. Mean distance «PIOL – corneal endothelium» was 2.19±0.19mm, «PIOL – natural lens» – 0.92±0.15mm, temporal «PIOL edge – corneal endothelium» – 1.55±0.18mm and nasal «PIOL edge – corneal endothelium» – 1.53±0.18mm. In 10 of 31 eyes (6 of 16 patients) it was found that both the nasal and the temporal «PIOL edge – corneal endothelium» parameters were below 1.5mm. Using the step method of linear discriminant analysis a formula (reliable with P<0.005) and a simplified algorithm were calculated to predict the risk of a «dangerous» Cachet PIOL position in the anterior chamber of the eye. Based on our own clinical material a priori sensitivity and specificity of this formula were 100% and 95%, respectively. Conclusion . The current study showed that the existing patient selection criteria for the Cachet PIOL do not provide its safe position in some cases. The new prediction formula and algorithm allow timely identifying patients at risk early to enhance the efficiency and safety of this high myopia correction method.

The Conformal Camera in Modeling Active Binocular Vision

Primate vision is an active process that constructs a stable internal representation of the 3D world based on 2D sensory inputs that are inherently unstable due to incessant eye movements. We present here a mathematical framework for processing visual information for a biologically-mediated active vision stereo system with asymmetric conformal cameras. This model utilizes the geometric analysis on the Riemann sphere developed in the group-theoretic framework of the conformal camera, thus far only applicable in modeling monocular vision. The asymmetric conformal camera model constructed here includes the fovea’s asymmetric displacement on the retina and the eye’s natural crystalline lens tilt and decentration, as observed in ophthalmological diagnostics. We extend the group-theoretic framework underlying the conformal camera to the stereo system with asymmetric conformal cameras. Our numerical simulation shows that the theoretical horopter curves in this stereo system are conics that well approximate the empirical longitudinal horopters of the primate vision system.

How Subsurface Water Technologies (SWT) can Provide Robust, Effective, and Cost-Efficient Solutions for Freshwater Management in Coastal Zones

Freshwater resources in coastal zones are limited while demands are high, resulting in problems like seasonal water shortage, overexploitation of freshwater aquifers, and seawater intrusion. Three subsurface water technologies (SWT) that can provide robust, effective, and cost-efficient solutions to manage freshwater resources in the subsurface are evaluated using groundwater modelling and validation at field-scale: (1) ASR-coastal to store freshwater surpluses in confined brackish-saline aquifers for recovery in times of demand, (2) the Freshkeeper to counteract salinization of well fields by interception and desalination of upconing brackish groundwater, and (3) the Freshmaker to combine ASR and Freshkeeper to enlarge the volume of natural freshwater lenses for later abstraction. The evaluation indicates that SWT can be used in various hydrogeological settings for various hydrogeological problems like seawater intrusion, upconing, and bubble drift during ASR and have significant economic benefits. Although only sporadically applied to date, we foresee that SWT will stimulate (cost-)efficient and sustainable exploitation of various freshwater sources (like groundwater, rainwater, treated waste water, surface water) in coastal zones. Prolonged SWT testing in the current pilots, replication of SWT in other areas worldwide, and the development of technical and non-technical support tools are required to facilitate potential end-users in investment decision making and SWT implementation.

Prospects to regain the ability to accommodate

Over one billion people around the world are affected by presbyopia [1]. A major factor causing presbyopia is stiffening of the crystalline lens. Elasticity, as a material property of the crystalline lens matrix, is often expressed by the Young’s modulus, a unit for stiffness named after Thomas Young. Interestingly, Thomas Young also studied accommodation and developed an instrument to measure objectively the accommodative amplitude. In 1801 he concluded that Bin general, I have reason to think that the faculty diminishes to some degree as persons advance in life^ [2]. This phenomenon has been confirmed in later years by measuring the accommodative amplitude of thousands of subjects, and it was soon suggested that the decline in accommodative amplitude with age should be attributed to stiffening of the crystalline lens [3]. Traditionally, presbyopia is treated with reading spectacles or contact lenses, using bifocal contact lenses or some sort of monovision. More recently, laser refractive surgery has gained popularity as the procedure has options of using multifocality and monovision for treating presbyopia. Another and more invasive alternative is to perform clear lens extraction, in which the natural crystalline lens is replaced by a multifocal or accommodating intraocular lens or a by lens that extends the range of vision. Scleral approaches are also being explored [4]. A less invasive way to combat presbyopia, proposed in 1998 by Myers and Krueger, is to alter the properties of the crystalline lens by photoablation or photodisruption in the crystalline lens by a laser [5]. While mechanical changes in the lens material as a result of laser treatment were already foreseen [6], Krueger and co-workers demonstrated a change in pliability of the lens as a whole, suggesting that presbyopia may be alleviated or reversed [7]. So far, only moderate changes in pliability have been observed. A factor influencing the effect of the procedure is the geometrical pattern inside the lens that is treated by the laser. Studies have concentrated on cutting inside the lens, generating gliding planes along which internal deformations can take place [8]. The search for the optimal gliding planes that maximize lens pliability is the subject of the paper BFinite element modelling of radial lentotomy cuts to improve the accommodation performance of the human lens^ by Burd & Wilde in the current issue of in Graefe’s Archive for Clinical and Experimental Ophthalmology. Instead of experimental studies, e.g. using cadaver eyes, the authors use computational methods to compare the effects of different cutting geometries. Computational methods avoid issues with measurement uncertainties, as well as variance between test specimen and post mortem degradation of cadaver lenses. On the down side, the validity of computational outcomes depends heavily on the validity of the input parameters of the model: geometry, material properties, and boundary conditions. It has been well demonstrated by the same authors in previous studies that the way that the behavior of ocular tissues is modeled has a significant effect on the outcomes [9, 10]. In the current paper the authors demonstrate this once again, by modeling the behavior of the lens matrix in two different ways. First, they model the lens matrix as an incompressible material that is initially linear elastic, but becomes non-linear due to large deformations. This approach of modelling the mechanical behavior of the crystalline lens is most often used in current literature. Then, as an alternative, they introduce a poroelastic material model, which represents the lens matrix as a two-phase mixture of an incompressible fluid and a compressible hyperelastic solid matrix. Whether this is a more realistic * Henk A. Weeber henk.weeber@abbott.com

Ultraviolet or blue-filtering intraocular lenses: what is the evidence?

Cataract surgery was revolutionised by the introduction of modern intraocular lenses in the late 1940's. By the late 1960's to 1970's evidence had emerged that short-wavelength light caused phototoxicity at the retina and retinal pigment epithelium. By the early 1980's ultraviolet filters had been incorporated into intraocular lenses. This caused intense controversy, as there was concern that the UV-filtering chromophore might leach out into the eye causing toxicity. With the arrival of blue-filtering intraocular lenses (BFIOLs) in 1990's, a further debate was ignited as to their safety and potential disadvantages. Selecting the optimal performing intraocular lens to obtain the best visual performance with the fewest potential drawbacks has become complex and challenging for cataract surgeons and their patients with the wide choice of lenses available. Choosing a personalised lens to address astigmatism, presbyopia, spherical aberration, chromatic aberration, and potentially to shield the retina from short-wavelength light is now possible. The potential benefits and possible side effects of these different innovations emphasise the importance of assessing the evidence for their clinical utility, allowing the surgeon and the patient to weigh-up the risk benefit ratio and make an informed decision. The BFIOLs were developed to reduce cyanopsia, address chromatic aberration, and improve contrast sensitivity in different lighting conditions, as well as to prevent short-wavelength light reaching the retina thus potentially reducing the risk of developing age-related macular degeneration. Further design development of the BFIOLs was to mimic the natural crystalline lens absorption and transmittance properties in adulthood. Multiple publications have reported on the potential benefits and pitfalls of implanting a blue-filtering lens. The potential disadvantages raised in the literature over the last 25 years since their introduction, regarding compromise of visual function and disruption of the circadian system, have been largely dispelled. The clear benefits of protecting the retina from short-wavelength light make a BFIOLs a sensible choice. The purpose of this article presented at the Cambridge symposium 2015 is to review the literature on this subject.

Biomimetic Accommodating Intraocular Lens Using a Valved Deformable Liquid Balloon.

Presbyopia is a common age-related condition that prevents people from focusing on near objects. The etiology of presbyopia continues to be debated, but the end effect of all postulated mechanisms is the lack of deformation of the human lens. Using our understanding of the biomechanical properties of the natural human lens, we created a unique accommodating intraocular lens. Although this lens can be used for lenticular disease such as myopia and hyperoperopia, this study addresses the needs of cataract patients with presbyopia. The lens was implanted into presbyopic human cadaver eyes. Focal length of the lens was measured with simulated muscle contraction. Lens dimensions were measured using artificial tissue and a finite-element analysis (FEA) to simulate accommodation. Lens power was measured at various fill volumes. Accelerated soak testing for an equivalent of 7.4years was performed and lens weight and optical transmittance were measured. Previously presbyopic human eyes were able to accommodate between 2.0 and 7.4 diopters after lens implantation. FEA and lens measurements demonstrated a change in curvature of the anterior and posterior portions of the lens during accommodation. After accelerated aging, lens weight remained unchanged and optical transmission was 96%. Lens power increased with fill volume. A deformable liquid lens reversed presbyopia, can be individualized by optically adjusting for each patient, is stable for long periods of time, and is compatible with minimally invasive surgical techniques. A deformable liquid-filled lens can significantly improve accommodation over the presbyopic natural lens.

Vignetting and negative dysphotopsia with intraocular lenses in "far peripheral vision".

At very large visual angles, vignetting can occur at the edge of an intraocular lens (IOL), because it is much smaller than the natural crystalline lens that it replaces. Ray trace calculations show that, by 80-90deg of input visual angle, it is possible that about half the light is no longer focused by the IOL. This may create curved, peripheral, shadowlike regions, which are a clinical characteristic of negative dysphotopsia. The imaging characteristics for this "far peripheral vision" region are different from those of a phakic eye, whether or not negative dysphotopsia is experienced.

Sutured Posterior Chamber IOL Fixation in the Absence of Capsular Support, First Described in 1954

By implanting the first IOL in 1949 Ridley's intention was to replace the opaque crystalline lens with a "lenticulus" exactly the size and the shape of the natural lens in the same physiological location in the posterior chamber. Still not resolved at that time was the fixation of the "pseudophakos" following intracapsular cataract extraction and the centration on the posterior capsule or, respectively, on residues of the anterior capsule following extracapsular cataract surgery. We describe the first attempts in 1954 of fixating a posterior chamber IOL following intracapsular extraction using a suture technique. Selective literature research via PubMed was undertaken and additional literature retrieved by a manual search was included. The conventional opinion that suture fixation of intraocular lenses was carried out since the 1980s and that Pearce in 1975 and Shearing in 1977 solved this problem by using haptics made of polypropylene is not quite correct: In 1954, by using a thin wire anchored in the IOL material, the British ophthalmologist, T. G. W. Parry, managed the first suture fixation of a Ridley IOL in the posterior chamber. This remarkable medical historical innovation was however overshadowed by the rapid development of intraocular lenses, from iris-fixated lenses ("collar stud": Epstein 1954, "iris-clip": Binkhorst 1959), anterior chamber lenses (Baron 1952, Strampelli 1953) to three-piece lenses for capsular bag fixation by Pierce and Shearing in the 1970s. However it becomes obvious that already in the 1950s it was possible to correct aphakia in cases with inadequate capsular support.

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

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

Bilateral pseudoexfoliation deposits on intraocular lens implants.

We present a rare case of bilateral pseudoexfoliative deposits on both intraocular lens (IOL) implants in an 83-year-old woman with no other associated pathology, 5 years after cataract surgery. Pseudoexfoliation syndrome is the most common cause of secondary open-angle glaucoma worldwide and these deposits are usually found on the natural lens. The fact that pseudoexfoliative deposits have been found on IOL implants implies the need for a thorough examination in pseudophakic patients, for it could be the only sign of secondary glaucoma.

Ocular Straylight: A Determinant of Quality of Life in the Elderly?

Intra-ocular straylight can cause decreased visual functioning, and it may cause diminished vision-related quality of life (VRQOL). This cross-sectional population-based study investigates the association between straylight and VRQOL in middle-aged and elderly individuals. Multivariable linear regression analyses were used to assess the association between straylight modeled continuously and cutoff at the recommended fitness-to-drive value, straylight ≥ 1.4 log(s), and VRQOL. The study showed that participants with normal straylight values, straylight ≤ 1.4 log(s), rated their VRQOL slightly better than those with high straylight values (straylight ≥ 1.4 log(s)). Furthermore, multivariable regression analysis revealed a borderline statistical significant association (p = .06) between intra-ocular straylight and self-reported VRQOL in middle-aged and elderly individuals. The association between straylight and self-reported VRQOL was not influenced by the status of the intra-ocular lens (natural vs. artificial intra-ocular lens after cataract extraction) or the number of (instrumental) activities of daily living that were reported as difficult for the elderly individuals.

Preoperative automatic visual behavioural analysis as a tool for intraocular lens choice in cataract surgery.

Cataract is the main cause of blindness, affecting 18 million people worldwide, with the highest incidence in the population above 50 years of age. Low visual acuity caused by cataract may have a negative impact on patient quality of life. The current treatment is surgery in order to replace the natural lens with an artificial intraocular lens (IOL), which can be mono- or multifocal. However, due to potential side effects, IOLs must be carefully chosen to ensure higher patient satisfaction. Thus, studies on the visual behavior of these patients may be an important tool to determine the best type of IOL implantation. This study proposed an anamnestic add-on for optimizing the choice of IOL. We used a camera that automatically takes pictures, documenting the patient's visual routine in order to obtain additional information about the frequency of distant, intermediate, and near sights. The results indicated an estimated frequency percentage, suggesting that visual analysis of routine photographic records of a patient with cataract may be useful for understanding behavioural gaze and for choosing visual management strategy after cataract surgery, simultaneously stimulating interest for customized IOL manufacturing according to individual needs.

Biomaterials for ocular reconstruction

Synthetic materials have played a significant role in ophthalmic applications to improve vision for many years. This has been in four main areas in ophthalmology: ocular surface reconstruction, lens replacement, vitreous replacement and structural support and cell transplantation in the retina. Corneal replacement therapies have been developed using both synthetic acrylic-based materials and more recently naturally derived materials such as amniotic membrane. Intraocular lenses as a replacement for the natural lens post cataract surgery has been used for many years. Newer developments include the opportunity to use gels so that the lenses can accommodate but these need improving in terms of the cross-linking chemistry. Silicone oils have been used as long-term tamponade agents as vitreous replacements but recent developments in their properties has enhanced the clinical outcomes and further research into their use as drug delivery vehicles will be a major advancement. Regenerative medicine therapies to repopulate the retina to repair and replace specific cell layers require the optimisation of synthetic scaffolds and this is a major area for development. Recent developments in biomaterials have emphasised the importance of the physical, chemical and mechanical properties specific to a particular ophthalmic application. Materials science has a critical role in developing strategies to overcome vision loss.

Double image in far peripheral vision of pseudophakic eye as source of negative dysphotopsia.

Some intraocular lens (IOL) patients report seeing "dark shadows" at visual angles that are larger than 60°-70°. Raytrace models of the pseudophakic eye show that light starts to miss the IOL at large visual angles because the implant diameter of about 6mm is much smaller than the natural crystalline lens diameter of 9.5mm. This light forms a second displaced image on the peripheral retina. To evaluate the appearance of the image, raytrace software was used to image an illuminated window onto the highly curved retina, and a method was developed to project the image back to object space for evaluation on a flat surface. Only a single schematic eye was evaluated monochromatically and the low resolution of the peripheral retina was not modeled, but the simulated images depict a shadow-like phenomenon at similar visual angles to reports of "negative dysphotopsia."