Optical radiation and the eyes with special emphasis on children

The Sun is the most abundant source of optical radiation for the child eye. New hand-held visible lasers are a threat to the child eye. Some scientific data suggest that near infrared radiation may cause cumulative damage in the ocular lens. The child eye usually is exposed to ambient solar radiation, gazing at the horizon. Ambient Sun ultraviolet radiation (UVR) exposure to the child is complex due to atmospheric scattering and strong dependence on background reflection. Solar exposure causes biological damage, only by photochemical mechanisms. UVR exposure to a child eye is mainly a threat to the anterior segment of the eye, but also age dependently to the retina. Above threshold exposure to UVR, for short delay onset of damage, causes a toxic reaction on the surface of the eye, snow blindness, and cataract. Sub-threshold daily exposure to UVR over decades is associated with several ocular surface pathologies and eye lid cancer. Visible radiation is a threat to the retina. A single above threshold exposure, for short delay onset of damage to the retina causes immediate photochemical Type II retinal damage, Sun blindness. A single exposure of the retina to a very high intensity laser beam may cause thermal or thermo-mechanical damage in the retina. In environments with high irradiance of optical radiation, the child eye should be protected. Legislation and public information is required for avoidance of damage from high intensity laser systems. More research is urgently needed to exclude the potential hazard of near infrared radiation.     

The effects of simulating a realistic eye model on the eye dose of an adult male undergoing head computed tomography

In head computed tomography, radiation upon the eye lens (as an organ with high radiosensitivity) may cause lenticular opacity and cataracts. Therefore, quantitative dose assessment due to exposure of the eye lens and surrounding tissue is a matter of concern. For this purpose, an accurate eye model with realistic geometry and shape, in which different eye substructures are considered, is needed. To calculate the absorbed radiation dose of visual organs during head computed tomography scans, in this study, an existing sophisticated eye model was inserted at the related location in the head of the reference adult male phantom recommended by the International Commission on Radiological Protection (ICRP). Then absorbed doses and distributions of energy deposition in different parts of this eye model were calculated and compared with those based on a previous simple eye model. All calculations were done using the Monte Carlo code MCNP4C for tube voltages of 80, 100, 120 and 140 kVp. In spite of the similarity of total dose to the eye lens for both eye models, the dose delivered to the sensitive zone, which plays an important role in the induction of cataracts, was on average 3% higher for the sophisticated model as compared to the simple model. By increasing the tube voltage, differences between the total dose to the eye lens between the two phantoms decrease to 1%. Due to this level of agreement, use of the sophisticated eye model for patient dosimetry is not necessary. However, it still helps for an estimation of doses received by different eye substructures separately.     

alphaA- and alphaB-crystallins protect glucose-6-phosphate dehydrogenase against UVB irradiation-induced inactivation

alpha-Crystallin, a major eye lens protein, has been shown to function like a molecular chaperone by suppressing the aggregation of other proteins induced by various stress conditions. Ultraviolet (UV) radiation is known to cause structural and functional alterations in the lens macromolecules. Earlier we observed that exposure of rat lens to in vitro UV radiation led to inactivation of many lens enzymes including glucose-6-phosphate dehydrogenase (G6PD). In the present paper, we show that alpha-crystallin (alphaA and alphaB) protects G6PD from UVB irradiation induced inactivation. While, at 25 degrees C, there was a time-dependent decrease in G6PD activity upon irradiation at 300 nm, at 40 degrees C there was a complete loss of activity within 30 min even without irradiation. The loss of activity of G6PD was prevented significantly, if alphaA- or alphaB-crystallin was present during irradiation. At 25 degrees C, alphaB-crystallin was slightly a better chaperone in protecting G6PD against UVB inactivation. Interestingly, at 40 degrees C, alphaA- and alphaB-crystallins not only prevent the loss of G6PD activity but also protect against UVB inactivation. However, alphaA- and alphaB-crystallins were equally efficient at 40 degrees C in protecting G6PD.     

NASCA report 2: Longitudinal study of relationship of exposure to space radiation and risk of lens opacity

The NASA Study of Cataract in Astronauts (NASCA) was designed to measure the impact of exposure to space radiation on progression rates of cortical, nuclear, and posterior subcapsular cataract in U.S. astronauts who have flown in space and comparison groups of astronauts who had not flown in space, and subjects with a history of military aviation. We present our analyses of 5 years of data with an average of 3.8 exams per subject. All subjects had digital lens images with the Nidek EAS 1000 Lens Imaging System. Because of high variability and skewness of opacity measures, nonparametric methods were used to test for association between rates of opacification and space radiation exposure. First, median regression was used to collapse longitudinal data into robust estimates of progression rates (opacity severity compare to time for each eye of each subject). To quantify and test for a radiation effect, median regression with the dependent variable being the maximum of the two slopes (OD and OS) per subject was then used, adjusting for the confounding variables of age, nutritional, and sun-exposure histories. Median regression showed evidence of an association between the rate of cortical progression in the worse eye with radiation dose and age. The estimated median progression rate from space radiation being 0.25 ± 0.13% lens area/Sv/year (P = 0.062). We found no relationship between radiation exposure and progression of aggregate area of posterior subcapsular cataract or nuclear progression rates. However, longer follow-up may be needed to further understand any impact of space radiation on progression rates for posterior subcapsular cataracts and nuclear cataracts, and to characterize changes to visual acuity.     

Eye lens exposure to medical staff during endoscopic retrograde cholangiopancreatography

The paper presents a study of the radiation doses to eye lens of medical staff during endoscopic retrograde cholangiopancreatography (ERCP) procedures performed in a busy gastroenterology department. For each procedure the dose equivalent to the eye, exposure time, dose rate, Kerma Area Product and fluoroscopy time were recorded. Measurements were performed for a period of two months in four main positions of the operating staff, and then extrapolated to estimate annual doses. The fluoroscopy time per ERCP procedure varied between 1.0 min and 28.8 min, with a mean value of 4.6 min. The calculated mean eye dose per procedure varied between 34.9 μSv and 93.3 μSv. The results demonstrated that if eye protection is not used, annual doses to the eye lens of the gastroenterologist performing the procedure and the anesthesiologist can exceed the dose limit of 20 mSv per year.     

Use of subjective and nonsubjective methodologies to evaluate lens radiation damage in exposed populations — an overview

The general epidemiological acceptability of prevalence, or incidence, for assessing risk of radiation cataract development has dictated an almost exclusive dependence on cataract onset as a measure of cataractogenicity for given doses of radiation. The advent of instrumentation capable of acquiring images amenable to quantitative analyses offers the possibility of exploiting ``relative opacification' as an added, if not exclusive, parameter. This development is particularly important in efforts to assess populations such as that in the Altai, which are temporally far removed from their exposure and among whom there exists a large subset with extant cataracts. The new technologies, Scheimpflug and retroillumination imaging, combined with the application of the appropriate analytical algorithms can not only provide quantitative and nonsubjective assessment of lens transparency, but also serve as a means to immortalize the state of the pathology at the time of acquisition. Highly relevant to the assessment of an aging exposed population is the use of lens epithelial fragments as potential dosimeters. The material is routinely available as a result of cataract extraction procedures and is amenable to the application of a modified micronucleus (MN) assay. The MN assay in the lens has tremendous advantages over its use in other tissues for a number of reasons, not least of which is that lens MNs are extremely long-lived. Given the relative ease of application and its potential as a radiation bioindicator, the lens MN assay should be considered in any follow-up of populations exposed to ionizing radiation. Received: 10 October 1995 / Accepted in revised form: 19 January 1996     

Epidemiological studies of cataract risk at low to moderate radiation doses: (not) seeing is believing

The prevailing belief for some decades has been that human radiation-related cataract occurs only after relatively high doses; for instance, the ICRP estimates that brief exposures of at least 0.5-2 Sv are required to cause detectable lens opacities and 5 Sv for vision-impairing cataracts. For protracted exposures, the ICRP estimates the corresponding dose thresholds as 5 Sv and 8 Sv, respectively. However, several studies, especially in the last decade, indicate that radiation-associated opacities occur at much lower doses. Several studies suggest that medical or environmental radiation exposure to the lens confers risk of opacities at doses well under 1 Sv. Among Japanese A-bomb survivors, risks for cataracts necessitating lens surgery were seen at doses under 1 Gy. The confidence interval on the A-bomb dose threshold for cataract surgery prevalence indicated that the data are compatible with a dose threshold ranging from none up to only 0.8 Gy, similar to the dose threshold for minor opacities seen among Chernobyl clean-up workers with primarily protracted exposures. Findings from various studies indicate that radiation risk estimates are probably not due to confounding by other cataract risk factors and that risk is seen after both childhood and adult exposures. The recent data are instigating reassessments of guidelines by various radiation protection bodies regarding permissible levels of radiation to the eye. Among the future epidemiological research directions, the most important research need is for adequate studies of vision-impairing cataract after protracted radiation exposure.     

A miniscule optimized visual system in the Lower Cambrian

Simultaneously with the development of animal body plans, probably before the Precambrian, there was an explosive diversification of visual systems. Competition of performance in these visual systems was a critical factor in the evolution of life systems.
Here we analyse the visual system in the lobopod Miraluolishania haikouensis ( Liu et al ., 2004 ) from the Lower Cambrian Chengjiang Lagerstätte, Kunming, China. It consists of a very small eye with a miniscule lens. A physical problem lies in the fact that due to the usual refractive conditions of such a lens, it hardly represents an improvement of the visual quality over the basal pit- or pinhole camera eyes. To develop such a lavish visual system, however, would not have been of any value, if it achieved no more than an equal level or represented even a retrograde step in evolutionary progress. We show how this system may have allowed pattern recognition even under poor light conditions. Optimization of such a tiny eye is costly but is not 'a wasted effort' in evolution. In M. haikouensis ( Liu et al. , 2004 ), an excellently adapted miniscule visual system has become possible.     

The influence of operator position,height and body orientation on eye lens dose in interventional radiology and cardiology: Monte Carlo simulations versus realistic clinical measurements

ObjectiveThis paper aims to provide some practical recommendations to reduce eye lens dose for workers exposed to X-rays in interventional cardiology and radiology and also to propose an eye lens correction factor when lead glasses are used.MethodsMonte Carlo simulations are used to study the variation of eye lens exposure with operator position, height and body orientation with respect to the patient and the X-ray tube. The paper also looks into the efficiency of wraparound lead glasses using simulations. Computation results are compared with experimental measurements performed in Spanish hospitals using eye lens dosemeters as well as with data from available literature.ResultsSimulations showed that left eye exposure is generally higher than the right eye, when the operator stands on the right side of the patient. Operator height can induce a strong dose decrease by up to a factor of 2 for the left eye for 10-cm-taller operators. Body rotation of the operator away from the tube by 45°–60° reduces eye exposure by a factor of 2. The calculation-based correction factor of 0.3 for wraparound type lead glasses was found to agree reasonably well with experimental data.ConclusionsSimple precautions, such as the positioning of the image screen away from the X-ray source, lead to a significant reduction of the eye lens dose. Measurements and simulations performed in this work also show that a general eye lens correction factor of 0.5 can be used when lead glasses are worn regardless of operator position, height and body orientation.     

Asymmetries in the sense organs and central nervous system of the squid Histioteuthis

The visual system of Histioteuthis is markedly asymmetrical, in that the eyes and optic lobes are considerably larger on the left side, and the lens of the left eye is often yellower in colour than that of the right eye. At the histological level, the rhabdomes of the retinas of both eyes show the usual rectilinear pattern typical of cephalopods. Unlike other species described, however, the orientation of the pattern is not uniform over the retina. The optic lobes are well developed on both sides, again following the typical squid pattern, although the plexiform and inner granular layers are thicker on the left side. In life it is likely that the animals orient at an oblique angle with the arms downward, and the left eye pointing upwards and the right eye downwards, and the asymmetries of the visual system are probably related to this posture. No corresponding asymmetries in the statocysts or other parts of the central nervous system have, however, been detected     

Highly efficient transfection system for functional gene analysis in adult amphibian lens regeneration

The analysis of newt lens regeneration has been an important subject in developmental biology. Recently, it has been reported that the genes involved in the normal eye development are also expressed in the regenerative process of lens regeneration in the adult newt. However, functional analysis of these genes has not been possible, because there is no system to introduce genes efficiently into the cells involved in the regeneration. In the present study, lipofection was used as the method for gene transfer in cultured pigmented iris cells that can transdifferentiate into lens cells in newt lens regeneration. Positive expression of a reporter gene was obtained in more than 70% of cells. In addition, the aggregate derived from gene-transfected cells maintained its expression at a high level for a long time within the host tissue. To verify the effectiveness of this model system with a reporter gene in lens regeneration, Pax6, which is suggested to be involved in normal eye development and lens regeneration, was transfected. Ectopic expression of lens-specific crystallins was obtained in cells that show no such activity in normal lens regeneration. These results made it possible for the first time to analyze the molecular mechanism of lens regeneration in the adult newt.     

Centering mechanism for soft contact lenses

A soft contact lens, because of its elasticity, can re-center itself over the cornea after it has been displaced by a blink. In this paper, a potential energy method is used to simulate the centering mechanism. Specifications for commercially available soft contact lenses and realistic eye shapes are used for the examples. With this technique we can compare the centering attributes of different lens and eye geometries.     

硫酸糖胺聚糖(Sulfated Glycosaminoglycans)在花背蟾蜍眼早期形态发生中的合成

本文用放射自显影追踪注射入胚胎的~(35)S-硫酸盐的方法,研究了花背蟾蜍早期形态发生时眼的各部分组织和细胞外基质中的硫酸糖胺聚糖(Sulfated Glycosaminoglycans简称:硫酸GAG)的合成,并分析了其在眼形态发生中的作用。结果表明:1.在眼早期形态发生时,合成的硫酸GAG主要是硫酸软骨素。2.眼各部分组织中在即将分化时硫酸GAG合成率增高,分化开始后逐渐下降到原基形成时的水平。3.在晶状体被诱导时,在视杯和晶状体相互贴近的组织及两者间的细胞外基质中硫酸GAG的合成率明显增加,提示这是晶状体诱导的重要因素。4.角膜上皮形成时即向角膜上皮下层和细胞外基质分泌硫酸GAG;角膜上皮透明时,合成更多的硫酸角质素。     

Correlation between eye lens doses and over apron doses in interventional procedures

Measurements of eye lens dose using over apron dosimeters with a geometric correction factor is an international accepted practice. However, further knowledge regarding geometric correction factors in different contexts is required. The authors studied the correlation between eye lens dose and over apron dosimetry for different medical specialties in eleven hospitals, using a standardized protocol, two independent over apron dosimeters (worn at chest and at neck levels) and a dedicated calibration procedure. The results show good correlation between subjects working on the same medical specialty for 5 specialties: Interventional Radiology, Vascular Surgery, Vascular Radiology, Hemodynamics and Neuroradiology. The geometric correction factors resulting from this study could be used to estimate eye lens dose using over apron dosimeters, which are more comfortable than eye lens dosimeters, as reported by the study subjects, as long as the increased uncertainty of the over apron dosimetry compared to the dedicated eye lens dosimetry is acceptable.     

Particle radiation alters expression of matrix metalloproteases resulting in ECM remodeling in human lens cells

Relatively low doses of space radiation have been correlated with an increased incidence and earlier appearance of cataracts in space travelers. The lens is a radiosensitive organ of the body with a very obvious late end point of radiation damage—cataract. However, many molecular changes occur in the lens soon after radiation exposure and long before the appearance of an opacification. The goal of our research is to elucidate early mechanisms associated with particle radiation-induced cataractogenesis, with the ultimate goal of developing countermeasures. Normal, cultured non-immortalized human lens cells were grown on matrix-coated plastic tissue culture vessels and irradiated with particle beams at Lawrence Berkeley National Lab (LBNL) or at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Lab. Samples were harvested at different times after radiation exposure. Using a focused genetic approach, total RNA and protein extracts from control and irradiated samples were processed and probed for the expression of genes associated with extracellular matrix (ECM) proteases. Matrix metalloproteinases (MMPs) have previously been studied in adult postmortem human lenses, in post-cataract intraocular lens (IOL) surgery capsular bags and with immortalized human lens cell cultures. Significant differences exist in the expression pattern with these various model systems. We have evidence for the cell stage-specific expression of MMP family of genes during lens fiber differentiation, and for radiation-induced alterations in the misregulation of MMP expression. Our data indicate that radiation exposure may lead to differences in the expression of radiation stress responses, which may impact selective ECM remodeling and cell differentiation     

Delay of uv-induced eye lens protein damage in guinea pigs by dietary ascorbate

Large accumulations of postsynthetically oxidized proteins are observed in the aged and cataractous eye lens. Ascorbate has previously been used to delay photooxidative damage in vitro. The goals of this study were (1) to confirm that dietary ascorbate can be used to enhance lens ascorbate levels and (2) to determine if lenses with enhanced ascorbate can better withstand photooxidative stress in the form of ultraviolet (UV) light exposure. Guinea pigs were placed on high dietary ascorbate (HDA), 50 mg/day, and low dietary ascorbate (LDA), 2 mg/day, for 21 weeks. Lenses from HDA animals were found to contain 3.3 times more ascorbate than LDA animals. Prior to irradiation, SDS-PAGE protein profiles and exopeptidase activity in HDA and LDA lens soluble proteins were indistinguishable. However upon exposure to UV light, more protein damage (e.g., high-molecular-weight aggregates and enhanced loss of exopeptidase activity) was seen in lens preparations from LDA as compared to HDA animals. These results suggest that ascorbate protects lens components against cataract-like and agerelated postsynthetic changes in vivo. As in previous tests on lens preparations, attenuated exopeptidase activity was observed before protein aggregation.     

Influence of small molecules on the photo-stability of water soluble porcine lens proteins

The eye lens is a biconvex structure composed of lens fibres, cells that lack of blood and nerve supply and of any organelle, allowing for a high concentration of water soluble proteins that determine the lens transparency and refractive index. The lens water soluble protein pool in mammals is composed of α-, β-, and γ-crystallins, the latter being involved in calcium homeostasis and having structural importance, the first playing a crucial role in preventing protein aggregation and the consequent lens obfuscation, which leads to the clinical outcome of cataract. Among different factors, oxidative stress, free radicals, and reactive oxygen species (ROSs) generated by the exposure to UV light are widely recognized to cause cataract formation. Taking advantage of synchrotron radiation circular dichroism, fluorescence, and circular dichroism spectroscopies, in the present study we investigate the influence of different small molecules with the potential to either quench ROS generation or to stabilize protein conformation. Therefore, ascorbic acid, an excellent antioxidant agent already present in the eye aqueous humour, has been tested along with ceftriaxone, mannitol and trehalose, which osmolyte activity was demonstrated interfering with model proteins misfolding. Our results showed that ascorbic acid strongly inhibits the ROS production without, however, preserving the native protein structure, whereas mannitol had no effect on the ROS production but retained better the secondary structure of WS proteins. Collectively, the use of a mixture of ascorbic acid and mannitol could be used to better protect eye lens proteins from ROS damage preventing the cataract onset.     

The effect of melatonin on eye lens of rats exposed to ultraviolet radiation

We investigated the influence of exogenously administered melatonin on adult rats eye lenses exposed to ultraviolet radiation (UV) A and B ranging from 356-254 nm irradiation at 8 microW/cm(2). Rats exposed to this range of UV for 15 min for one week showed a significant (P<0.05) reduction in antioxidant enzymes activities; superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and elevated (P<0.001) lipid peroxidation served as an index of cellular damage by free radicals. UV-radiation significantly (P<0.001) elevated calcium ions (Ca(2+)) and lactate dehydrogenase (LDH) activity in lenses. Depleting animals of their stores of important intracellular antioxidant and elevating lenticular Ca(2+) by UV irradiation, may be the main cause of lens opacification. Melatonin injection with radiation significantly reduced (P<0.05) lipid peroxidation, Ca(2+) and (P<0.001) for LDH. When melatonin was injected after radiation, SOD and GSH-Px enzyme activities increased significantly (P<0.01), and lipid peroxidation, Ca(2+) levels and LDH activities were reduced significantly. Melatonin injection after UV radiation was as effective as melatonin treatment concurrent with UV irradiation. We conclude that melatonin may protect the eye lens from the damaging effects of UV exposure, and its actions protect lens from oxidative stress, elevating Ca(2+) levels, which are considered as an important causes of cataractogenesis.     

Structural changes in alpha-crystallin and whole eye lens during heating, observed by low-angle X-ray diffraction

Whole eye lens and alpha-crystallin gels and solutions were investigated using X-ray scattering techniques at temperatures ranging from 20 degrees C to 70 degrees C. In whole lens isolated in phosphate-buffered saline, the spacing of the dominant X-ray reflection seen with low-angle scattering was constant from 20 degrees C to 45 degrees C but increased at 50 degrees C from 15.2 nm to 16.5 nm. At room temperature, the small-angle X-ray diffraction pattern of the intact lens was very similar to the pattern of alpha-crystallin gels at near-physiological concentration (approximately 300 mg/ml), so it is reasonable to assume that the alpha-crystallin pattern dominates the pattern of the intact lens. Our results therefore indicate that in whole lens alpha-crystallin is capable of maintaining its structural properties over a wide range of temperature. This property would be useful in providing protection for other lens proteins super-aggregating. In the alpha-crystallin gels, a moderate increase in both the spacing and intensity of the reflection was observed from 20 degrees C to 45 degrees C, followed by an accelerated increase from 45 degrees C to 70 degrees C. Upon cooling, this effect was found to be irreversible over 11 hours. Qualitatively similar results were observed for alpha-crystallin solutions at a variety of lower concentrations.     

金鱼Prox1基因cDNA的克隆及其在眼睛发育中的表达分析

脊椎动物的Prox1基因,与果蝇的转录因子prospero同源。为了探讨Prox1基因在金鱼眼睛发生过程中的表达图式,我们从金鱼眼睛SMART库中克隆了Prox1cDNA。它全长共2851bp,编码739个氨基酸。组织分布研究表明,Prox1主要分布于眼、脑、心、肝、脾和肾中。整体原位杂交显示,Prox1mRNA首先是在晶体期的晶体原基中有转录,心跳期则在未成熟晶体的细胞中和视网膜的幼芽区可以检测到。晶体纤维形成后,它主要定位于视纤维层和内网织细胞层。免疫组化显示,心跳期Prox1蛋白的定位与mRNA相同,晶体纤维形成以后,Prox1蛋白主要定位在晶体上皮细胞内侧的晶体纤维上一个环状区域,与Prox1mRNA的定位不同。这说明,Prox1基因在晶体发生过程中有重要作用,且在晶体的不同发育时期起的作用可能有所不同。另外,Prox1在晶体发育过程中有一个从内向外的变化过程。