Posterior cataract induction by UV-B radiation in albino mice

UV-B radiation (290-320 nm) was very effective at inducing posterior cortical cataracts in mice similar to those seen in the human senile lens. UV-A radiation, in contrast, was at most weakly cataractogenic. The posterior opacities induced by UV-B began to appear 5-6 months after daily exposure to 8 X 10-6 W cm-2 for 12 hr per day or 10-4 W cm-2 for 1 hr per day. Progression was more rapid following the more intense exposure rate. The cataracts developed without any apparent damage to the cornea. A hypothesis of how damage sustained by the epithelium results in posterior opacities is presented.     

Photooxidation of the nonenzymatic browning products in calf lens alpha-crystallin.

The browning reaction (or advanced glycation) of calf lens alpha-crystallin generates chromophores which absorb light at wavelengths above 300 nm. They display an absorption shoulder above 300 nm, a positive circular dichroism band at 320-340 nm, and a blue fluorescence at 460 nm (Ex = 370 nm). Upon irradiation by UV-A light at a wavelength of 320-350 nm, the intensity of the absorption shoulder displayed an increase, but both circular dichroism and blue fluorescence intensities decreased. It appears that browning chromophores were photolyzed and converted to species which absorb more light at 320-330 nm, but are optically inactive. The browning products are thus susceptible to photooxidation from radiation of light above 300 nm and add an oxidative stress to the lens proteins.     

Photochemical bleaching of fluorescent glycosylation products

We have examined the effect of visible light and ultraviolet on the non-enzymatic glycosylation of lysine in vitro. Glucose and L-lysine were mixed and incubated under white light, UV-A, UV-B, or in the dark. During 15 days of incubation in the dark, a heterogeneous mixture of intensely brown chromophores developed, with a dominant fluorescence excitation maximum at 350 nm and emission maxima near 425 nm. The process was delayed or inhibited to a moderate extent by white light, whereas under UV-A and UV-B this effect was more pronounced. We conclude that non-enzymatic glycosylation can be photochemically modulated by both visible light and ultraviolet.     

Cataract classification

Opacifications of the eye lens — generally defined as cataracts — develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of ‘cataract formation’ cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The ‘objective methods’ for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lensbefore visible (and therefore subjectively recognizable) opacifications occured. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.     

Ultraviolet radiation as a risk factor for cataract and macular degeneration

The human eye is constantly exposed to sunlight and artificial lighting. Light transmission through the eye is fundamental to its unique biological functions of directing vision and circadian rhythm, and therefore, light absorbed by the eye must be benign. However, exposure to the intense ambient radiation can pose a hazard particularly if the recipient is over 40 years of age. This radiation exposure can lead to impaired vision and transient or permanent blindness.Both ultraviolet-A (UV-A) and UV-B induce cataract formation and are not necessary for sight. Ultraviolet radiation is also a risk factor for damage to the retinas of children. The removal of these wavelengths from ocular exposure will greatly reduce the risk of early cataract and retinal damage. One way this may be easily done is by wearing sunglasses that block wavelengths below 400 nm (marked 400 on the glasses). However, because of the geometry of the eye, these glasses must be wraparound sunglasses to prevent reflective UV radiation from reaching the eye. Additional protection may be offered by contact lenses that absorb significant amounts of UV radiation.In addition to UV radiation, short blue visible light (400-440 nm) is a risk factor for the adult human retina. This wavelength of light is not essential for sight and not necessary for a circadian rhythm response. For those over 50 years old, it would be of value to remove these wavelengths of light with specially designed sunglasses or contact lenses to reduce the risk of age-related macular degeneration.     

Age-related changes in the absorption characteristics of the primate lens

PURPOSE: To quantitate aging of the primate lens by changes in the absorption characteristics that are related to the yellowing of lens protein. METHODS: The lenses of lower primates and humans were sectioned anterior to posterior every 0.25 mm, and the UV-visible spectrum of each section was measured to determine the cumulative spectra along the visual axis. The ratio of the absorbance at 320 nm (formed with aging) to the absorbance at 365 nm (present in the young lens) was correlated with the age of the lens. RESULTS: In the young primate UV-B is transmitted to the retina, and UV-A is transmitted to the nucleus of the lens. By puberty, changes in the absorption characteristics of the lens that are associated with the yellowing of lens protein prevented most of the UV-B from reaching the retina and by the eighth decade, the transmittances at 320 and 365 nm to the nucleus of the lens were approximately 40% and 79%, respectively. A linear relationship between the ratio of absorbance at 320 to 365 nm and age was found for both lower primates and humans to the age of 80 years. This is surprising, because the maximum life span of the lower primate is approximately 35 years, whereas humans may live 100 years. CONCLUSIONS: These data suggest that the observed spectral changes associated with the yellowing of the lens are the result of a chronological process, such as chemical or photochemical modifications, not biological aging.     

Measurement of light transmission of human limbal epithelial cells cultured on human amniotic membranes

PURPOSE: To measure the light transmission properties of human limbal epithelial cell sheets (LECSs) cultured on human amniotic membranes (AMs) and compare them with those of AMs with and without amniotic epithelium. METHODS: Total light transmission of 3 kinds of tissue (LECSs, intact AMs, denuded AMs) was measured in the 250- to 800-nm range by using a spectrophotometer. RESULTS: The percent transmission of each kind of tissue decreased gradually and continually throughout the spectrum as the wavelength shortened and dropped rapidly at 300 nm to less than 20% at 250 nm. All tissues transmitted more than 70% of light in the wavelength region greater than 400 nm and more than 90% in that greater than 600 nm. The percent transmission spectrum of all tissues showed identical curves in the visible light and UV-A regions. However, the percent transmission of LECSs was lower than that of either intact or denuded AMs in the UV-B and UV-C regions. CONCLUSIONS: In the visible and UV-A light region, the percent transmission profiles of amnion-related tissues (LECSs, intact AMs, denuded AMs) are not altered by the presence of either amniotic epithelium or multilayered limbal corneal epithelium. However, the presence of multilayered limbal corneal epithelium, but not amniotic epithelium, on amniotic stroma reduced UV-B and -C transmission significantly. Further study concerning light transmission and other physical properties of LECSs is necessary to fully understand the ocular physiology of eyes grafted with such newly developed bioengineered tissues.     

In vivo studies on the effect of UV-radiation on the eye lens in animals

Ultraviolet light is a non-ionizing radiation that induces photochemical reactions in the tissue. Its spectral A and B ranges are partially absorbed by the cornea and/or lens thus causing damage on the cellular, cell physiological and molecular level. UV-A does not seem to damage the cornea permanently and its effects in the lens have a very prolonged latency period. Typical reactions of the cornea are oedema, punctate keratitis (photoelectric keratitis) and neovascularization. In the lens all reactions that could be evidenced, were located in the epithelium and in the outer cortical fiber cells.In vivo UV-A induces swelling and slight vacuolation of the anterior suture system, but apart from these transient effects, only very limited permanent damage could be demonstrated. UV-B induces the formation of an anterior subcapsular cataract, starting also with vacuolation of the suture system. These morphological characteristics can be visualized at the slitlamp microscope. Histologically, sutural irregularities (UV-A) and epithelial hyperplasia with capsular multiplication (UV-B) as well as desintegration of the anterior suture system could be observed. Patho-physiologically, a reduction of lens fresh weight (UV-B) as well as changes of the equilibrium of reduced and oxidized glutathione (GSH/GSSG) could be demonstrated. On the protein-biochemical level, changes in the ratio of water-soluble versus water-insoluble protein could be evidenced, as well as effects on specific crystallin fractions, namelyα-crystallin. In addition, the appearance of a newly synthetized 31 kDa protein could be demonstrated in UV-B irradiated mice.     

Cataract classification

Opacifications of the eye lens — generally defined as cataracts — develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of cataract formation cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The objective methods for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lensbefore visible (and therefore subjectively recognizable) opacifications occured. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.     

Establishment of the mouse as a model animal for the study of diabetic cataracts

The purpose of the present study was to investigate the suitability of using the mouse, a species known to have a low lens aldose reductase activity, as a model animal for studying the pathogenesis of diabetic cataract. Earlier studies with diabetic rats whose cataract development is much faster can only partially explain the etiology of cataracts in humans where lens aldose reductase is substantially low. CD-1 mice were injected intraperitoneally with streptozotocin according to Rossini's method. Blood glucose levels were estimated after 7 days, and animals having blood glucose between 300 and 400 mg/dl were selected for further experiments. Development of lenticular opacity was followed by examining the animals every 3-4 weeks by direct ophthalmoscopy, slitlamp examination and Scheimpflug photography. Additionally, the animals were sacrificed at appropriate intervals, eyes enucleated and subjected to morphological studies. The presence of refractive changes and early cataract in the diabetic mice was initially ascertained by the distorted appearance of the grid pattern when seen through the isolated lenses. Early cataracts were visible on slitlamp examination and by ophthalmoscopy as early as 3-4 weeks after the establishment of diabetes. Advanced opacity was clearly documentable by photography after 5-6 months. Similar to that in other species, a single layer of anterior epithelial cells abutting the anterior capsule was seen in the histological sections of normal mouse lenses. On the contrary, the epithelium in the diabetic lens was multilayered, and numerous nucleated cells were visible in the superficial anterior cortex. These studies therefore suggest that further studies with mice may throw additional light on the contribution of diabetes in the pathogenesis of cataracts in low lens aldose reductase models.     

Changes in the lens related to the reduction of transparency

Changes in the lens will cause fluctuations in refractive index which, in turn, will increase the scattering of light. Such alterations were studied by quantitative microradiography, electron microscopy, and a light scattering technique. Certain types of opacities of the human cortical cataract were shown to start as an enlargement of the intercellular spaces, followed by the breakage of lens cell membranes, loss of some of the protein matrix and the creation of large refractive interfaces between zones with different protein concentrations. The human nuclear cataract differed completely from the various types of cortical opacities. Here, the only change detected was an aggregation of the protein molecules into dense clusters of about 500–1000 Å in diameter. Aggregates of some similarity were also found in the cold cataracts within the nucleus of calf lenses. In these two kinds of nuclear cataracts the reduced transparency can be explained by the presence of these aggregates which are visible under electron microscope.     

In vivo studies on the effect of UV-radiation on the eye lens in animals

Ultraviolet light is a non-ionizing radiation that induces photochemical reactions in the tissue. Its spectral A and B ranges are partially absorbed by the cornea and/or lens thus causing damage on the cellular, cell physiological and molecular level. UV-A does not seem to damage the cornea permanently and its effects in the lens have a very prolonged latency period. Typical reactions of the cornea are oedema, punctate keratitis (photoelectric keratitis) and neovascularization. In the lens all reactions that could be evidenced, were located in the epithelium and in the outer cortical fiber cells.In vivo UV-A induces swelling and slight vacuolation of the anterior suture system, but apart from these transient effects, only very limited permanent damage could be demonstrated. UV-B induces the formation of an anterior subcapsular cataract, starting also with vacuolation of the suture system. These morphological characteristics can be visualized at the slitlamp microscope. Histologically, sutural irregularities (UV-A) and epithelial hyperplasia with capsular multiplication (UV-B) as well as desintegration of the anterior suture system could be observed. Patho-physiologically, a reduction of lens fresh weight (UV-B) as well as changes of the equilibrium of reduced and oxidized glutathione (GSH/GSSG) could be demonstrated. On the protein-biochemical level, changes in the ratio of water-soluble versus water-insoluble protein could be evidenced, as well as effects on specific crystallin fractions, namely-crystallin. In addition, the appearance of a newly synthetized 31 kDa protein could be demonstrated in UV-B irradiated mice.     

Matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in the human lens: implications for cortical cataract formation

PURPOSE: To characterize the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) in human cortical cataract and to determine whether there is a correlation with the localization of cortical cataract. To evaluate the expression and activity of MMPs and TIMPs after cytokine and UV-B exposure in a human lens epithelial cell line. METHODS: Twenty-eight human donor eyes with cortical cataract and 21 normal human donor eyes were photographed. Thirteen cortical cataract and six normal lenses were immunohistochemically analyzed for MMP-1, -2, -3, and -9 and TIMP-1, -2, and -3. Twelve fresh cortical cataract and 12 normal lenses were divided into quadrants to quantify, by ELISA, the expression of MMP-1, -2, -3, and -9 and TIMP-1. Three fresh cortical cataract and three control lenses were assessed for MMP-1, -2, and -9 activity by SDS-PAGE zymography. Human lens epithelial cells (HLE-SRA-01/04) were exposed to proinflammatory cytokines and UV-B radiation to determine the protein expression profiles of MMP-1, -2, -3, and -9 and TIMP-1 and -2. RESULTS: Immunohistochemical analysis revealed specific localization of MMP-1 within lens epithelium and cortical lens fibers of cortical cataract. Normal lenses had equally low MMP-1, -2, -3, and -9 and TIMP-1, -2, and -3 immunoreactivity, expression, and activity in all lens quadrants. IL-1 and TNF-alpha upregulated the expression of MMP-2, -3, and -9, and UV-B upregulated the expression of MMP-1 in the SRA-01/04 HLE cell line. CONCLUSIONS: This is the first study to localize the expression of MMP-1 in cataracts with clinically observed opacification in vivo and to examine the expression induced by UV-B, in vitro.     

Ultraviolet radiation for the sterilization of contact lenses

Two sources of ultraviolet (UV) radiation with peak wavelengths in the UV-C or UV-B ranges were compared for their ability to sterilize contact lenses infected with Pseudomonas aeruginosa, Streptococcus pneumoniae, Acanthamoeba castellani, Candida albicans, and Aspergillus niger. Also examined was the effect of prolonged UV light exposure on soft and rigid gas permeable (RGP) contact lenses. The UV-C lamp (253.7 nm, 250 mW/cm2 at 1 cm) was germicidal for all organisms within 20 minutes but caused destruction of the soft lens polymers within 6 hours of cumulative exposure. UV-C caused damage to RGP lenses in less than 100 hours. The UV-B lamp (290-310 nm, 500 mW/cm2 at 1 cm) was germicidal for all organisms tested (except Aspergillus) with a 180-minute exposure and caused less severe changes in the soft lens polymers than did the UV-C lamp, although cumulative exposure of 300 hours did substantially weaken the soft lens material. RGP materials were minimally affected by exposure to 300 hours of UV-B. Ultraviolet light is an effective germicidal agent but is injurious to soft lens polymers; its possible utility in the sterilization of RGP lenses and lens cases deserves further study.     

Ultraviolet radiation transmittance of the mouse eye and its individual media components

Recently, the mouse has become the preferred animal model in ophthalmic research. Therefore, there is a need for enhanced understanding of the mouse eye to validate its use in different experimental setting. The purpose of this study was to determine the ocular transmittance of the whole mouse eye, the cornea and the crystalline lens, particularly in the ultraviolet radiation (UVR) wavebands. This was carried out using a non-cuvette based fiber optic spectrometer system and the resulting transmittance curves were compared with published cone spectral response curves and mouse ocular transmittance data. First, transmittance curves of the whole mouse eye were measured by removing a small disc of sclera from the posterior pole to provide an anterior to posterior optical path. No statistical difference was found between left and right eye in each of the four mice sampled, therefore, all eight eyes were included in the final statistical analysis. The average of five test measurements from each left and right eye for the four test mice showed a transmittance cut off at approximately 310 nm. Secondly, the cornea with a scleral rim was excised and transmittance curves obtained for all eight eyes. This data showed an average transmittance cut off at 280 nm for the cornea. Similarly measured data for the excised crystalline lens showed UVR transmittance down to 310 nm. The good correlation between total ocular UVR transmittance and the sum of the individually measured components (i.e. the cornea and the crystalline lens) supported the validity of our method and its findings. This experiment demonstrated that the mouse cornea transmits more UV-B (280-315 nm) than the rabbit and the human corneal transmittance. The mouse crystalline lens on the other hand showed a cut off in the UV-B at 310 nm, which is at a much lower UV-B wavelength than the approximate UV-A (315-400 nm) cut off for the human crystalline lens at around 390 nm. The increased transmittance of UVR in the mouse eye serves its vision, since the mouse has a cone photopigment peaking at approximately 350 nm. Due to the above stated differences between the mouse and the human it is concluded that the mouse is not an ideal model for the human eye in experiments involving UVR.     

In vivo autofluorescence. Measurements of human crystalline lenses with cataract and normal findings after excitation with monochromatic light]

In 25 eyes with nuclear cataract, 18 eyes with posterior subcapsular cataract, 25 eyes with cortical cataract, and 23 eyes without any pathological lens changes, the maximal fluorescence intensity was determined after excitation with monochromatic light at 365 nm, 405 nm, 436 nm, and 485 nm. The coefficient of variation was smaller than 5%. All eyes with cataract underwent cataract surgery a few days after the fluorescence measurements. The fluorescence spectrometer, especially constructed for in vivo measurements, consists of a modified slit lamp (Zeiss 75 SL) and an optical multichannel analyser (OMA) for gauging the data. The clinical trial was undertaken to determine whether, considering the influence of age, there is a difference between the fluorescence intensities in eyes with the above named cataracts and noncataractous eyes. The data were analyzed to determine the effect of age upon fluorescence intensity for all excitation wavelengths in both cataractous and noncataractous eyes. Age had an influence on the fluorescence intensities for all four excitation wavelengths. Assuming that the influence of age was not dependent on the state of the lens, it was quantified for all measurements and an "age-corrected" fluorescence intensity was calculated. The statistical analyses of these "age-corrected" fluorescence intensities revealed a significant difference (P < 0.001) for all of the types of cataracts examined and for normal eyes. The cataract types examined and the normal eyes showed differences in their fluorescence feature. To assess the fluorescence intensities obtained after excitation with the wavelengths mentioned above, one must take into consideration the influence of age on the measurements.     

The effects of sub-solar levels of UV-A and UV-B on rabbit corneal and lens epithelial cells

The purpose of this work was to establish whether exposing cultured rabbit corneal and lens epithelial cells to ultraviolet radiation equivalent to several hours under the sun would damage the cells. Confluent rabbit corneal epithelial cells were irradiated with broadband UV-A or UV-B, and confluent lens epithelial cells were irradiated with broadband UV-A. The maximum dose of UV-A was 6.3 J cm(-2) and that of UV-B was 0.60 J cm(-2). Damage to corneal epithelial cell was studied using the terminal deoxynucleotidyl transferase mediated dUTP-X nick end labeling (TUNEL) assay and damage to lens epithelial cell was studied using the single cell gel electrophoresis (comet) assay and trypan blue exclusion assay. Lipid peroxidation was assayed using the thiobarbituric acid reaction. Both UV-B and UV-A induced cell death in corneal epithelial cells with different latent periods. UV-A damage included cell death, decreased viability and increased lipid peroxidation of lens epithelial cell. In addition, UV irradiation of the corneal and lens epithelial cells decreased the activity of catalase to thirty to fifty percent of its original value, while the activities of glutathione peroxidase and superoxide dismutase did not decrease within experimental error. Thus, even sub-solar UV radiation can cause irreversible damage to corneal and lens epithelial cells.     

The effect of a 550 nm cutoff filter on the vision of cataract patients

The effect on visual function of an optical filter which absorbs essentially all visible wavelengths below 550 nm has been studied in a group of patients with moderate stage cataracts. Using a Snellen-type visual acuity chart with a blue background and orange letters, under both glare and non-glare conditions, the visual acuity of these patients was determined. Improvement in acuity was more striking under glare conditions than under standard (non-glare) conditions; in the former case it reached levels as high as 300% in a few patients. The level of the improvement seemed to be related both to cataract type and stage of cataract progression.     

Assessment of the epidemiological evidence that exposure to solar ultraviolet radiation causes cataract

In this paper an assessment is made of the evidence that exposure to solar ultraviolet radiation is causally associated with cataract. The evidence is reviewed separately for cortical, nuclear and posterior subcapsular cataract. The assessment examines the consistency and magnitude of an association, the dose-response relationship, supporting ecological data, and data from animal studies. Based on the assessment, it is concluded that there is sufficient experimental evidence that exposure to artificial sources of UV-B can cause cortical opacities in laboratory animals. However, there is only limited evidence that exposure to solar UV-B causes cortical opacities in humans. Similarly, there is only limited evidence that exposure to solar UV-B causes posterior subcapsular cataract in humans. The epidemiological evidence is consistent in suggesting tha nuclear cataracts are not causally associated with exposure to solar UV-B.     

Assessment of the epidemiological evidence that exposure to solar ultraviolet radiation causes cataract

In this paper an assessment is made of the evidence that exposure to solar ultraviolet radiation is causally associated with cataract. The evidence is reviewed separately for cortical, nuclear and posterior subcapsular cataract. The assessment examines the consistency and magnitude of an association, the dose-response relationship, supporting ecological data, and data from animal studies. Based on the assessment, it is concluded that there is sufficient experimental evidence that exposure to artificial sources of UV-B can cause cortical opacities in laboratory animals. However, there is only limited evidence that exposure to solar UV-B causes cortical opacities in humans. Similarly, there is only limited evidence that exposure to solar UV-B causes posterior subcapsular cataract in humans. The epidemiological evidence is consistent in suggesting tha nuclear cataracts are not causally associated with exposure to solar UV-B.