Acute effects of ultraviolet-B irradiation on the corneal surface of the pigmented rabbit studied by quantitative scanning electron microscopy

Poly (Ethylene Glycol) Methyl Ether Methacrylate-Based Hydrogel and Cerium(IV) Oxide Nanoparticles as Ophthalmic Lens Material

The functional hydrogel lens containing 2-hydroxyethylmethacrylate (HEMA) was manufactured by thermal polymerization. The physical properties of the produced hydrogel lens were measured and analyzed. In this study, HEMA, ethylene glycol dimethacrylate (EGDMA), and azobisisobutyronitrile (AIBN) were used for thermal copolymerization. Additionally, poly (ethylene glycol) methyl ether methacrylate (PEGMEMA), 3-(Triethoxysilyl) propyl isocyanate (TEPI), and cerium(Ⅳ) oxide nanoparticles were used as additives to make a functional hydrogel lens. The mixture was heated at 100 °C for 90 min to produce the hydrogel ophthalmic lens by the cast mold method. The resulting physical properties showed that the water content and refractive index of the sample were in the ranges of 38.06~42.11% and 1.426~1.436, respectively. The addition of cerium oxide nanoparticles lowered the contact angle and allowed the hydrogel lens to block UV light. The tensile strength was also improved by 52.13% through cerium oxide nanoparticles, and up to 123.4% by using TEPI. Based on the results of this study, the produced ophthalmic lens is suitable for durable, UV-blocking high-performance lenses.

Short term effects of continuous lighting on the cornea of cage-reared laboratory rabbits

This study was to assess the impact on the cornea and eye blink activity of adapting rabbits to continuous lighting (CL) compared to a 14:10 light:dark cycle. Female New Zealand White rabbits (2 to 2.5 kg) were maintained under a light: dark (L:D) cycle or switched to continuous fluorescent lighting (CL) for an average of 17 +/- 2 days. Animal behaviour in their cages was manually recorded using an event marker and in vivo slitlamp biomicroscopy at 40× undertaken in mid-afternoon. Animals were then euthanized and the corneas prepared for scanning electron microscopy (SEM). From images taken at 500× from the central region of the corneas, the number of exfoliating (desquamating) cells and the relative number of different cells with light, medium or dark reflexes were assessed for the corneal epithelial surface, while the number of cells/unit area were assessed for both corneal epithelium and endothelium. Exposure to continuous lighting was associated with higher number of eye blink events (15.7 vs 8.2/15 min) and mild corneal surface alterations evident by biomicroscopy with higher numbers of intra-epithelial 'granules' (32 +/- 14 vs. 4 +/- 3/sq. mm). SEM revealed low numbers of exfoliating cells on the corneal epithelial surface in all CL-adapted animals, but not in L:D controls. Trends were observed for there to be slightly higher numbers of epithelial cells/unit area, higher numbers of small light reflex cells and lower numbers of larger dark reflex cells in CL animals. The corneal endothelium showed no obvious adverse effects in CL-adapted animals but the percentage of 'hexagonal' cells was slightly higher compared to L:D controls. The results indicate that even a short period of exposure of laboratory-raised rabbits to constant lighting can be associated with mild adverse effects on the corneal epithelial surface.

Malachite Green Induced Ultrastructural Corneal Lesions in Cyprinus carpio and Its Amelioration Using Emblica officinalis

Malachite green, a multi-purpose dye induces cyto-toxicity upon its entry and bioaccumulation in tissues. A semi-static chronic (60 days) bioassay was conducted by exposing Cyprinus carpio to sublethal concentration of the dye and Emblica officinalis in four experimental groups viz control, malachite green, E. officinalis, and malachite green + E. officinalis. Effect of dye on the cornea was investigated considering ultra-structural alterations owing to its direct contact to the pollutant in the aquatic medium. SEM studies on corneal epithelium revealed broken continuity of pavement cells, shrunk microplicae, increased intra-microplicae distance, globularization and epithelial uplifting, thereby affecting the integrity of corneal surface and tear film adherence. Whereas dietary supplementation with the plant extract served to restore cytoarchitecture with appearance of large number of regenerating cells. Both lesions and restoration were found to be duration dependent. Thus, E. officinalis can be considered as an effective ameliorant against malachite green induced toxicity.

Stratified corneal limbal epithelial cells are protected from UVB-induced apoptosis by elevated extracellular K⁺

The goal of this study was to determine whether elevated [K(+)] protects stratified corneal epithelial cells from entering apoptosis following exposure to ambient levels of UVB radiation. Human corneal limbal epithelial (HCLE) cells were stratified to form multilayered constructs in culture. The cells were exposed to UVB doses of 100-250 mJ/cm(2) followed by incubation in medium with 5.5-100 mM K(+). The protective effect of K(+) was determined by measuring the caspase-3 and -8 activity and TUNEL staining of the stratified HCLE constructs. In response to UVB exposure, activation of apoptotic pathways peaked at 24 h. Caspase-8 in stratified cells was activated by exposure to UVB at 100-250 mJ/cm(2), and activity was significantly reduced in response to 50 or 100 mM K(+). Caspase-3 was activated in the stratified cells in response to 100-250 mJ/cm(2) UVB and showed a significant reduction in activity in response to 25, 50 or 100 mM K(+). DNA fragmentation, as indicated by TUNEL staining, was elevated after exposure to 200 mJ/cm(2) UVB, and decreased following incubation with 25-100 mM K(+). These results show that in a culture system that models the intact corneal epithelium, elevated extracellular K(+) can reduce UVB-induced apoptosis which is believed to be initiated by loss of K(+) from cells. This is the basis of damage to the corneal epithelium caused by UVB exposure. Based on these observations it is suggested that the relatively high K(+) concentration in tears (20-25 mM) may play a role in protecting the corneal epithelium from ambient UVB radiation.

Intraocular lens short wavelength light filtering

There is increasing interest in the effects of reactive oxygen species ('free radicals') in ageing, both in the body overall and specifically in the eye. Cataract and age-related macular degeneration (AMD) are two major causes of blindness, with cataract accounting for 48 per cent of world blindness and AMD accounting for 8.7 per cent. Both cataract and AMD affect an older population (over 50 years of age) and while cataract is largely treatable provided resources are available, AMD is a common cause of untreatable, progressive visual loss. There is evidence that AMD is linked to exposure to short wavelength electromagnetic radiation, which includes ultraviolet, blue and violet wavelengths. The ageing crystalline lens provides some protection to the posterior pole because, as it yellows with age, its spectral absorption increasingly blocks the shorter wavelengths of light. Ultraviolet blocking intraocular lenses (IOLs) have been the standard of care for many years but a more recent trend is to include blue-blocking filters based on theoretical benefits. As these filters absorb part of the visible spectrum, they may affect visual function. This review looks at the risks and the benefits of filtering out short wavelength light in pseudophakic patients.

UV dose-dependent caspase activation in a corneal epithelial cell line

PURPOSE

To characterize the UVB radiation-dependent patterns of caspase activation and cell death in SV 40 immortalized corneal epithelial cells.

METHODS

Cell death in immortalized human corneal epithelial cells (T-HCEC) was induced by exposure to low (50 mJ/cm2) and high (450 mJ/cm2) doses of UVB. Cell death morphology was examined by fluorescence microscopy using the cell death marker propidium iodide (PI). Apoptosis of T-HCEC was analyzed by DNA fragmentation assays, and enzyme activity was measured for caspase 3 and 9 by fluorophotometry. Changes in mitochondrial inner membrane potential were measured by flow cytometry using the fluorescent marker, rhodamine 123. Redistribution of cytochrome c, the upstream trigger of caspase 9, was measured in the cytosol fraction of T-HCEC following irradiation.

RESULTS

PI staining revealed a fragmented staining pattern of the nucleus consistent with apoptosis in detached cells irradiated with low-dose UVB, while cells receiving high dose UVB demonstrated round, well bordered staining of the nucleus. Flow cytometry revealed irreversible mitochondrial damage in the high dose group shown by decreased levels of rhodamine 123 fluorescence. Cells in the low-dose group had intact mitochondrial inner membrane potential, increased cytosolic cytochrome c, and showed a significantly higher rate of DNA fragmentation and caspase activation than the high dose group.

CONCLUSION

Low dose UVB caused cytochrome c redistribution, caspase activation and apoptosis of corneal epithelial cells, which was not observed at high irradiation levels of UVB.

Lymphocytic reaction to ultraviolet radiation on rabbit conjunctiva

We examined the clinical and histological effects of controlled UV radiation on the conjunctiva and cornea of rabbit eyes by duration of exposure (0.5-4 hours daily for 5 consecutive days). Longer UV exposure (day 1-day 5) was associated with increased conjunctival redness, corneal erosion, edema and opacity. This study shows that UV irradiation leads to clinical and histological changes which may reflect an immune reaction to damaged epithelial cells.

The corneal epithelial surface in the eyes of vertebrates: Environmental and evolutionary influences on structure and function

The smooth optical surface of the cornea is maintained by a tear film, which adheres to a variety of microprojections. These microprojections increase the cell surface area and are thought to improve the movement of oxygen, nutrients, and metabolic products across the outer cell membranes. However, little is known of these structural adaptations in vertebrates inhabiting different environments. This field emission scanning electron microscopic study examined the cell density and surface structure of corneal epithelial cells across 51 representative species of all vertebrate classes from a large range of habitats (aquatic, amphibious, terrestrial, and aerial). In particular, we wished to extend the range of vertebrates to include agnathans and some uniquely Australian species, such as the Australian lungfish (Neoceratodus forsteri), the Australian galah (Eolophus roseicapillus), the Australian koala (Phascolarctos cinereus), and the rat-tailed dunnart (Sminthopsis crassicaudata). Epithelial cell densities ranged from 28,860 +/- 9,214 cells mm(-2) in the flathead sole Hippoglossoides elassodon (a marine teleost) to 2,126 +/- 713 cells mm(-2) in the Australian koala (a terrestrial mammal), which may indicate a reduction in osmotic stress across the corneal surface. A similar reduction in cell density occurred from marine to estuarine to freshwater species. The structure and occurrence of microholes, microplicae, microridges, and microvilli are also described with respect to the demands placed on the cornea in different environments. All species that spend significant periods out of an aquatic environment possess microvilli and/or microplicae. These include all of our species of Mammalia, Aves, Reptilia, Amphibia, and even one species of Teleostei (Australian lungfish). Well-developed microridges occur only in teleosts in high osmolarity environments such as marine or estuarine habitats. Clear interspecific differences in corneal surface structure suggest a degree of adaptive plasticity, in addition to some phylogenetic trends.

Surfactant and UV-B-induced damage of the cultured bovine lens

PURPOSE

To evaluate in vitro methods for testing the toxicity of the surfactants, sodium dodecyl sulfate (SDS) and benzalkonium chloride (BAK), and Ultraviolet (UV)-B radiation to the bovine lens.

METHODS

Lenses were dissected from bovine eyes--obtained from a local abattoir--and incubated in M199 culture medium at 37 degrees C, with 4% CO(2) and 96% air atmosphere. For the SDS and BAK experiments, the lenses (n = 153) were exposed directly to 0.001%, 0.01%, 0.1%, and 1.0% solutions for 15 min. These lenses were then rinsed five times each with saline and medium. Another group of lenses (n = 36) was irradiated with broadband UV-B at energy levels of 1.0 and 2.0 J/cm(2) (0.445 and 0.89 J/cm(2) in the biologically effective energy levels). For all of the above experiments, lens optical quality and cellular viability of lens epithelial cells were evaluated.

RESULTS

The analysis of optical quality, using a scanning laser in vitro assay system, of exposed lenses treated with SDS and BAK at concentrations of 0.01%, 0.1%, and 1.0%, and with UV-B at energy levels of 0.445 and 0.89 J/cm(2) showed a dose- and time-dependent increase in back vertex distance (BVD) variability, indicating loss of sharp focus in comparison with control lenses. Both 0.001% SDS and 0.001% BAK-treated lenses did not show any optical damage until 8-days after exposure. Lenses treated with 0.01% SDS showed recovery from optical damage 6-days later after exposure. Optical damage was not shown immediately for UV-B-exposed lenses. The Alamar Blue assay data for SDS, BAK and UV-B-exposed lenses, except the 0.001% SDS treated lens group, showed also dose- and time-dependent decreases in cellular viability in comparison with the control lenses, and there was no cellular recovery during the entire culture period. Lenses treated with 0.001% SDS did not show biological damage until 8-days after exposure. It appears that cellular changes appeared earlier than optical changes.

CONCLUSIONS

The findings suggest that cultured bovine lenses can be evaluated by assays that probe optical properties and cellular function after exposure to surfactants and UV-B irradiation, and that the optical and biological assay methods are valuable for in vitro mild ocular toxicity research.

Ultraviolet radiation absorption of intraocular lenses

OBJECTIVES

To record and compare the spectral transmittance curves of intraocular lenses (IOLs) made out of polymethyl methacrylate (PMMA), acrylic, hydrogel, and silicone from different manufacturers; to evaluate their ultraviolet radiation absorption capacities; and to contrast the recorded transmittance curves with that of the natural lens.

DESIGN

Experimental study.

METHODS

We studied 17 different 21-diopter IOLs. A high-performance spectrophotometer with a diffuse transmittance accessory was employed to measure the transmittance of wavelengths from 200 nm to 800 nm through a 1.5-mm aperture.

MAIN OUTCOME MEASURES

Transmittance percentage and 10% transmittance cutoff wavelength.

RESULTS

All studied IOLs offered good ultraviolet radiation protection in the ultraviolet C (200-280 nm) and ultraviolet B (280-315 nm) ranges. A number of silicone, PMMA, and acrylic lenses showed different and, at times, only low degrees of absorption in the ultraviolet A (315-400 nm) range.

CONCLUSIONS

Intraocular lenses of different compositions have ultraviolet radiation absorption characteristics different from that of the crystalline lens.

Lactoferrin protects against UV-B irradiation-induced corneal epithelial damage in rats

PURPOSE

Lactoferrin supplementation suppresses ultraviolet light B (UV-B)-induced oxidation of cultures of human corneal epithelial cells. To investigate the protective effect of lactoferrin containing eyedrops against UV-B-induced corneal damage in vivo, we examined lactoferrin efficacy in a rat UV-B keratitis model.

METHODS

Sprague-Dawley rats were irradiated with >10 kJ/m2 after anesthetization, and then corneal epithelial defect was observed at 24 h postirradiation. The pre- or postapplication of vehicle or lactoferrin-containing eyedrops was performed, and then corneal epithelial damage was scored based on fluorescein staining.

RESULTS

Posttreatment with lactoferrin did not inhibit the extent of corneal damage and did not affect wound healing. However, pretreatment by topical application of lactoferrin suppressed development of a corneal epithelial defect induced by UV-B irradiation in rats.

CONCLUSION

These results suggest that the presence of lactoferrin in human tear fluid may inhibit UV-induced corneal epithelial damage.

Apoptosis in UV-exposed rabbit corneas

PURPOSE

Apoptosis was studied in rabbit corneas as a possible mechanism of cell death after photokeratitis induced by different UV wavelengths.

METHOD

Fourteen albino rabbit corneas were exposed to 280- and 310-nm UV radiation (UVR) in 10-nm full wavebands at doses that cause biomicroscopically significant keratitis (0.12 J/cm2 for 280 nm and 0.47 J/cm2 for 310 nm). Animals were killed 24 and 76 h after exposure. Corneas were processed for light and transmission electron microscopy and in situ end labeling of fragmented DNA by using a modification of the TUNEL technique.

RESULTS

Corneas exposed to 280-nm UVR showed TUNEL-positive staining only in epithelial cells and superficial keratocytes at 24 and 76 h after irradiation. Twenty-four hours after 310-nm UVR exposure, TUNEL-positive staining was present in the epithelial cells, keratocytes throughout the entire thickness of the central stroma, and in endothelial cells. Seventy-six hours after exposure to 310-nm UVR, keratocytes disappeared throughout the whole thickness of the damaged stroma. Only a few epithelial cells were TUNEL positive at that time. Transmission electron microscopy (TEM) verified the occurrence of apoptotic nuclei and cells.

CONCLUSION

Apoptosis appears to be a mechanism of corneal cell death after UVR. The 310-nm UVR caused more extensive damage to the corneal stroma and endothelium than did the 280-nm UVR.

Scanning electron microscopy study of the tarsal and orbital conjunctival surfaces compared to peripheral corneal epithelium in pigmented rabbits

The mammalian palpebral conjunctiva has not been systematically evaluated by scanning electron microscopy (SEM). The upper eyelid of female grey rabbits (2 kg) was fixed in its extended conformation at 15.00 h; some corneas were prepared with the same fixative protocol. The corneal epithelium, within 1 mm of the limbus, is a mosaic of small-to-large (average cell area of 693 m2) squamous cells with light, medium or dark appearance due to different densities of cell surface microplicae. The tarsal conjunctiva was a 1.5 to 3 mm wide mosaic of small (average cell area of 86 microm2) non-desquamating polygonal cells having distinctive light and dark appearances due surface microplicae. The orbital portion of the palpebral conjunctiva is also composed of small (average cell area of 87 microm2) non-desquamating polygonal cells but with a uniform medium-grey appearance due to a relatively consistent density of surface microvilli. Several types of intercellular pore-like openings were also present across the palpebral surface but not the corneal epithelial surface. Very small type 1 pores (1.5 to 5 microm diameter) were present at a density of 480 to 760 / mm2 for the tarsal and 80-160 / mm2 for orbital conjunctiva. Slightly larger (2.5 to 18 microm diameter) type 2 pores with distinct borders were present at 120-200 / mm2 across the orbital conjunctiva. Very large (10-109 microm diameter) type 3 (Henle) pores were present at 40 to 280/mm2 especially at the tarsal/orbital transition zone. Type 4 pores (goblet cell orifices) were oval with a peripheral ring of microvilli and were present at 40 to 160/mm2 for tarsal and 800 to 1600/mm2 for orbital conjunctiva. The rabbit palpebral conjunctival surface is thus distinctly different from the peripheral corneal epithelium across which it slides following eyelid closure.

Modulation of HLA-DR and CD1a expression on human cornea with low-dose UVB irradiation

PURPOSE

To evaluate the effects of low-dose UVB irradiation of HLA and CD1a expression and the toxic effects of UVB on human corneas.

METHODS

24 pairs of human corneas from 24 donors were studied. One cornea from each pair was randomly irradiated with UVB (100 mJ/cm2) after enucleation. All corneas were then organ-cultured for 2, 7, 14 or 21 days. Endothelium was studied after enucleation and organ culture. Following preservation, corneas were evaluated by means of light microscopy, morphometry and TEM. HLA and CD1a staining was performed using an immuno-alkaline-phosphatase technique.

RESULTS

Endothelial cell loss during organ culture averaged 9.1% in the UVB group and 9.2% in the control group (NS). The number of rosette and reformation figures (p = 0.004) and the coefficient of variation (p = 0.014) were higher in the control group. Epithelial sloughing was more accentuated in the UVB group. We observed the same moderate ultrastructural injuries in both groups. In the epithelium, the average number of HLA-DR+ cells per field was 0.12 in the UVB group and 0.42 in the control group (p = 0.035). In the stroma, these figures were respectively 1.04 and 1.34 (p = 0.026). In the epithelium, the average number of CD1a + cells was respectively 0. 025 and 0.078 (p = 0.019). In the preservation mediums, the average percentage of CD1a + cells was 0.07% in the UVB group and 0.27% in the control group (p = 0.014).

CONCLUSIONS

Low-dose UVB (100 mJ/cm2) decreases HLA-DR and CD1a expression of organ-cultured human corneas and induces moderate corneal injuries. Low-dose UVB might be useful for preventing allograft rejection.

In vitro UVB irradiation of bovine crystalline lens causes cell damage and reduction in leucine aminopeptidase activity in lens epithelium

Past studies in our laboratory have shown that low levels of UVB can cause changes in the optical properties of organ cultured ocular lenses, while other research has shown that in vitro UV radiation causes decreases in leucine aminopeptidase activity in homogenates of crystalline lens material. Therefore we have investigated whether there is a relationship between such decreases in enzyme activity and changes in lens optics and structure. Organ cultured bovine lenses were irradiated with low doses of UVB, and lens optics, histology and leucine aminopeptidase activity (leucine beta-naphthylamide hydrolysis at pH 7.5) were assessed daily. Lenses irradiated with 0.1 J cm-2 UVB showed a decrease of about 30% in leucine aminopeptidase activity 1 h after irradiation, while changes in lens optics were not observed until at least 24 h after irradiation. Histological examination of the lens anterior epithelium revealed changes in epithelial cells ranging from pyknotic nuclei to large areas of cell fragmentation. The results of this study suggest that a decrease in soluble aminopeptidase activity in lens epithelial cells may be a direct result of the epithelial cell damage rather than an effect of UVB on the enzyme per se.

Evidence for heterogeneity in a small squamous cell type ('light' cells) in the rabbit corneal epithelium--a scanning electron microscope study. Corneal epithelial squamous cells

The rabbit corneal epithelial surface, as viewed by scanning electron microscopy (SEM), is composed of a mosaic of polygonal cells with different appearances (light, medium and dark) with the lighter cells having a characteristically high density of microplicae. From the central zone of the corneal epithelial surface of 16 female New Zealand White rabbits (2 kg), the lighter-appearing cells had an average area of 108 +/- 47 microns2 (n = 567, +/-SD). A subgroup of atypical lighter cells had an average area of 294 +/- 67 microns2 (n = 53) compared to typical light cells of 88 +/- 12 microns (n = 514). These atypical lighter cells had fused microplicae at their periphery (instead of a uniform arrangement of densely packed microplicae), tended to be rounder in shape (as opposed to being angular), could show signs of desquamation and were not decorated with the epithelial craters found on almost all (92%) other light cells. All of these features are suggestive of these atypical lighter cells being the terminal phenotype of the light cells just prior to desquamation from the ocular surface. The observation of the desquamation of lighter cells supports a hypothesis that they constitute a distinct sub-population of cells at the corneal epithelial surface.

Identification of topographical variations in the sizes of cells in a monolayer--application to corneal endothelium

The cells in the corneal endothelium, do not have a constant geometric arrangement but rather can be organized into widely different patterns or arrays. Conventional statistical analyses of variance in cell size can be used to report that the endothelial mosaic is homogeneous (homomegethous) or heterogeneous (polymegethous) but do not identify the source of the homogeneity or its loss. We present methods that allow for both identification and graphical presentation of regional homogeneity or heterogeneity in the endothelial cell monolayer. Single electron micrographs (containing 180 cells) were taken at the central region of the rabbit corneal endothelium and cell areas measured by planimetry. Special computer programs allow progressive evaluation of variance in all cell areas across the set of cells. Several examples are presented in detail to illustrate different degrees and types of variance for sets of endothelial cells that have small to extremely large ranges of areas (i.e. coefficient of variation values ranging from 0.12 to over 1.0). There also appears to be a mathematically predictable relationship between cell surface area and the number of cell sides. The methods developed should be applicable to quantitative comparisons of cells in monolayers or tissue sections.

The effect of ultraviolet-B irradiation on the cell shedding rate of the corneal epithelium

In this study cell shedding rates of the corneal epithelium were determined in vitro following a single suprathreshold dose of ultraviolet-B irradiation. Rabbit corneas were excised and superfused in pairs. The epithelial and endothelial surfaces were bathed with solutions containing essential ions and adjusted to appropriate pH and osmolality. One cornea in each pair was irradiated, while the other cornea served as a control. Shed cells were periodically collected from the corneal surface and the shedding rate determined by counting the number of cells in a 50 min time period. Following a latent period of about 3 h, the epithelial shedding rate accelerated, and remained elevated for at least 8 h after irradiation. This result suggests that suprathreshold doses of ultraviolet-B irradiation disrupt the normal orderly cell shedding process and homeostatic equilibrium of the corneal epithelium. The elevated cell shedding rate exposes subsurface nerve endings and causes the characteristic pain of photokeratitis.

Topographical differences in cell area at the surface of the corneal epithelium of the pigmented rabbit

Corneas from female pigmented rabbits were prepared for scanning electron microscopy at 15.00 h. The superior-temporal and inferior-nasal quadrants were evaluated at 500X at-stage magnification, normal to the corneal surface, at central, paracentral and peripheral sites. Non-parametric statistical analyses of the histograms of cell surface areas at each site from seven corneas revealed significant differences between the three sites but not between superior and inferior quadrants.