Exposure to subthreshold dose of UVR-B induces apoptosis in the lens epithelial cells and does not in the lens cortical fibre cells.

PURPOSE: The aim of this study was to investigate in which part of the lens in vivo exposure to subthreshold dose of UVR-B radiation induces apoptosis. METHODS: Twenty 6-week-old female albino Sprague-Dawley rats were exposed to subthreshold dose (1 kJ/m2 ) of UVR-B unilaterally and killed at 120 hr after exposure. Lenses were enucleated and dissected on three regions: the lens epithelium, the cortex and the nucleus. The lens nucleus then was removed. Apoptosis markers p53 and caspase 3 were used to study apoptosis in the lens regions. qRT-PCR and Western blot were utilized to analyse the lenses. RESULTS: TP53 and CASP3 mRNA expressions are increased in exposed lenses, both in the lens epithelium and in the cortex regions, in relation to non-exposed lenses. Expression of p53 protein is increased in exposed lens epithelium in relation to non-exposed lens epithelium. Caspase 3 protein is expressed in exposed lens epithelial cells, while it is not expressed in non-exposed lens epithelial cells. p53 and caspase 3 proteins are not expressed in either exposed nor non-exposed lens fibre cells. CONCLUSION: Exposure to UVR-B increases mRNA transcription of apoptosis marker p53 in vivo in both regions of the lens and of apoptosis marker caspase 3 in the lens cortex. Exposure to UVR-B increases p53 and caspase 3 proteins expression just in the lens epithelium. In vivo exposure to subthreshold dose of UVR-B induces apoptosis in the lens epithelial cells and does not in the lens fibre cells.

Evolution of damage in the lens after in vivo close to threshold exposure to UV-B radiation: cytomorphological study of apoptosis.

The purpose of the present study was to investigate cataractogenesis and recovery of lens damage after in vivo close to threshold ultraviolet (UV)-B radiation around 300 nm. Eighty six-week-old albino Sprague-Dawley rats were familiarized to a rat restrainer five days prior to exposure. Groups of non-anesthetized rats were exposed unilaterally to 8 kJ/m(2) UVR-300 nm. The animals were sacrificed at 1, 7, 48 and 336h following exposure. The lenses were extracted for imaging of dark-field lens macro anatomy and measurement of intensity of forward lens light scattering to quantify lens opacities. Three exposed lenses and one non-exposed lens from each time interval were examined with light and transmission electron microscopy (TEM). Macro anatomy and lens light scattering revealed that all contralateral non-exposed lenses were clear. The degree of lens opacity (difference in lens light scattering between exposed and non-exposed lenses) increased during the 336h, reaching a plateau towards the end of the observation period. Light microscopy and TEM demonstrated that apoptotic features appeared in the epithelium already 1h after UVR exposure, and small vacuoles were seen in the outer cortex. Epithelial damage occurs during the first 48h after exposure and is followed by regenerative repair at 336h post-exposure. Apoptotic epithelial cells were phagocytized by adjacent epithelial cells. Cortical fiber cells exhibited increasing damage throughout the observation period without any clear repair after 336h. In conclusion, acute UVR-induced cataract is partly a reversible. Lens epithelium is a primary target for UVR exposure. Damage to cortical fiber cells remained irreversible.

NASA study of cataract in astronauts (NASCA). Report 1: Cross-sectional study of the relationship of exposure to space radiation and risk of lens opacity.

The NASA Study of Cataract in Astronauts (NASCA) is a 5-year longitudinal study of the effect of space radiation exposure on the severity/progression of nuclear, cortical and posterior subcapsular (PSC) lens opacities. Here we report on baseline data that will be used over the course of the longitudinal study. Participants include 171 consenting astronauts who flew at least one mission in space and a comparison group made up of three components: (a) 53 astronauts who had not flown in space, (b) 95 military aircrew personnel, and (c) 99 non-aircrew ground-based comparison subjects. Continuous measures of nuclear, cortical and PSC lens opacities were derived from Nidek EAS 1000 digitized images. Age, demographics, general health, nutritional intake and solar ocular exposure were measured at baseline. Astronauts who flew at least one mission were matched to comparison subjects using propensity scores based on demographic characteristics and medical history stratified by gender and smoking (ever/never). The cross-sectional data for matched subjects were analyzed by fitting customized non-normal regression models to examine the effect of space radiation on each measure of opacity. The variability and median of cortical cataracts were significantly higher for exposed astronauts than for nonexposed astronauts and comparison subjects with similar ages (P=0.015). Galactic cosmic space radiation (GCR) may be linked to increased PSC area (P=0.056) and the number of PSC centers (P=0.095). Within the astronaut group, PSC size was greater in subjects with higher space radiation doses (P=0.016). No association was found between space radiation and nuclear cataracts. Cross-sectional data analysis revealed a small deleterious effect of space radiation for cortical cataracts and possibly for PSC cataracts. These results suggest increased cataract risks at smaller radiation doses than have been reported previously.

Spontaneous resolution of a traumatic cataract caused by an intralenticular foreign body.

A 49-year-old man presented with an intralenticular metal foreign body incurred while he was sawing wood. The metal chard had violated the lens capsule and was lodged in the cortex of the lens. It was removed using a lens-preservation technique during open-globe repair. Subsequently, a dense posterior cortical cataract developed, which spontaneously resolved over the ensuing months. The cataract had a cruciate configuration with wave-like disruption of the stromal lamellae. To our knowledge, this is the first case of spontaneous resolution of a cataract after capsule violation by an intralenticular foreign body. The unique appearance of the cataract and its unusual resolution led to a new theory of lens injury by shockwave.

Radiation cataracts: mechanisms involved in their long delayed occurrence but then rapid progression.

PURPOSE: This study was directed to assess the DNA damage and DNA repair response to X-ray inflicted lens oxidative damage and to investigate the subsequent changes in lens epithelial cell (LEC) behavior in vivo that led to long delayed but then rapidly developing cataracts. METHODS: Two-month-old C57Bl/6 female mice received 11 Grays (Gy) of soft x-irradiation to the head only. The animals' eyes were examined for cataract status in 30 day intervals by slit lamp over an 11 month period post-irradiation. LEC migration, DNA fragment, free DNA retention, and reactive oxygen species (ROS) presence were established in the living lenses with fluorescent dyes using laser scanning confocal microscopy (LSCM). The extent and removal of initial LEC DNA damage were determined by comet assay. Immunohistochemistry was used to determine the presence of oxidized DNA and the response of a DNA repair protein in the lenses. RESULTS: This treatment resulted in advanced cortical cataracts that developed 5-11 months post-irradiation but then appeared suddenly within a 30 day period. The initially incurred DNA strand breaks were repaired within 30 min, but DNA damage remained as shown 72 h post-irradiation by the presence of the DNA adduct, 8-hydroxyguanosine (8-OHG), and a DNA repair protein, XRCC1. This was followed months later by abnormal behavior by LEC descendant cells with abnormal differentiation and migration patterns as seen with LSCM and fluorescent dyes. CONCLUSIONS: The sudden development of cortical cataracts several months post-irradiation coupled with the above findings suggests an accumulation of damaged descendants from the initially x-irradiated LECs. As these cells migrate abnormally and leave acellular lens surface sites, eventually a crisis point may arrive for lens entry of environmental O(2) with resultant ROS formation that overwhelms protection by resident antioxidant enzymes and results in the coagulation of lens proteins. The events seen in this study indicate the retention and transmission of progenitor cell DNA damage in descendant LEC. The cellular and molecular events parallel those previously reported for LSCM observations in age-related cataracts.

Cataracts among Chernobyl clean-up workers: implications regarding permissible eye exposures.

The eyes of a prospective cohort of 8,607 Chernobyl clean-up workers (liquidators) were assessed for cataract at 12 and 14 years after exposure. The prevalence of strictly age-related cataracts was low, as expected (only 3.9% had nuclear cataracts at either examination), since 90% of the cohort was younger than 55 years of age at first examination. However, posterior subcapsular or cortical cataracts characteristic of radiation exposure were present in 25% of the subjects. The data for Stage 1 cataracts, and specifically for posterior subcapsular cataracts, revealed a significant dose response. When various cataract end points were analyzed for dose thresholds, the confidence intervals all excluded values greater than 700 mGy. Linear-quadratic dose-response models yielded mostly linear associations, with weak evidence of upward curvature. The findings do not support the ICRP 60 risk guideline assumption of a 5-Gy threshold for "detectable opacities" from protracted exposures but rather point to a dose-effect threshold of under 1 Gy. Thus, given that cataract is the dose-limiting ocular pathology in current eye risk guidelines, revision of the allowable exposure of the human visual system to ionizing radiation should be considered.

Localization of cortical cataract in subjects of diverse races and latitude.

PURPOSE: To compare the characteristics of early cortical cataract localization in three groups in cataract epidemiologic surveys performed in Reykjavík, Melbourne, and Singapore. METHODS: Individuals who had right eyes with an area of cortical opacity less than 20% of the pupil when dilated 7 mm or more were selected as subjects. This included 197 subjects from the Reykjavík Eye Study, 231 from the Vitamin E, Cataract, and Age-Related Maculopathy (VECAT) study in Melbourne, and 92 from the Singapore-Japan Cooperative Cataract Study, all showing early-stage cataract in pupils dilated to 7 mm or more. Scheimpflug and retroilluminated photographs were used to locate opacities. Localization of cortical cataract was determined by dividing the retroillumination image into seven concentric circles with diameters of 1 through 7 mm, and eight sections of 45 degrees radial octants. The positive rate of opacification was then calculated for each quadrant. RESULTS: The highest positive rate of opacification was observed in the lower nasal quadrant in all groups. The relative risk of the prevalence of cortical opacity in the lower nasal oblique hemisphere to the upper temporal oblique hemisphere was the highest in the Singaporean subjects followed by those of Melbourne and then of Reykjavík. CONCLUSIONS: The prevalence of cortical cataract was higher in the lower nasal quadrant than in the other quadrants for all subjects of diverse race in three climatically different locations. This higher prevalence was most pronounced in subjects living at low latitude. These results support the view that solar UV exposure is a possible risk factor for development of human cortical cataract.

Light exposure and the risk of cortical, nuclear, and posterior subcapsular cataracts: the Pathologies Oculaires Liées à l'Age (POLA) study.

BACKGROUND: Exposure to light may be an important risk factor for the development of cataracts. OBJECTIVE: To present the relation of ambient solar radiation and professional and leisure exposures to light with the different types of cataracts. METHODS: Pathologies Oculaires Liées a l'Age (POLA) is a population-based study on cataract and age-related macular degeneration and their risk factors in 2584 residents of Sète (southern France). Cataract classification was based on lens examination at slitlamp according to Lens Opacities Classification System III. A questionnaire about light exposure was administered. RESULTS: After multivariate adjustment, participants who had higher ambient solar radiation had a 2.5-fold (95% confidence interval [CI], 1.2-5.0), 4.0-fold (95% CI, 2.0-8.0), and 2.9-fold (95% CI, 1.5-5.3) increased risk of cortical and mixed cataract and cataract surgery, respectively. Solar ambient radiation was not significantly associated with posterior subcapsular and nuclear cataracts. By contrast, posterior subcapsular cataracts were significantly associated with professional exposure to sunlight (odds ratio [OR], 1.63; 95% CI, 1.01-2.63) and frequent use of sunglasses (OR, 0.62; 95% CI, 0.43-0.90). Mixed cataract was also associated with professional exposure to artificial light (OR, 3.02; 95% CI, 1.03-8.82). CONCLUSION: Our study further confirms the role of sunlight exposure in the pathogenesis of cataract, in particular in its cortical localization.

Effects of UV-B radiation on a hereditary suture cataract in mice.

UV-B (290-320 um, lambda max = 305 nm) radiation and the Cat2ns (suture cataract) mutation in mice affect both the anterior lens epithelium and the formation of the suture. A low dose of UV-B radiation (2.2 Jcm-2) induces similar anterior subcapsular and cortical lens opacities in wild type as in heterozygous mutant mice. The UV-B treatment of the mutant lenses, however, leads to an increase in the number of epithelial cell layers in the anterior central part as compared to the wild type indicating a more severe form of the cataract formation in mutants. In addition, mutants demonstrate a predisposition for a rupture of the posterior lens capsule, because from 2.9 Jcm-2 and higher, this phenomenon could always be observed in the UV-B treated mutants, but never in the treated wild type mice. The protein biochemical analyses were performed by gel electrophoresis and isoelectric focusing of extracts of total lenses or from defined areas of the lens (lens slice technique). These covered the patterns of those proteins already synthesized before irradiation, which in irradiated lenses in no case evidenced a difference to the untreated control, neither in the wild type nor in the mutants. In contrast, by analysing specifically those proteins, which are synthesised after irradiation, in both treated groups a protein with a molecular mass of about 31 kDa becomes discernable in both treated groups. In addition, the cataractous lenses demonstrate a significantly enhanced overall synthesis of water-soluble proteins after irradiation, which might promote the rupture of the posterior capsule at the posterior pole. The present study offers for the first time the possibility to discriminate between endogeneous (genetic) effects and exogeneous (environmental) effects in cataractogenesis and to study their interactive effects. The first set of experiments demonstrated a clear intensification of the hereditary cataract by the UV-B treatment. The study supports the hypothesis that environmental stress (like UV-B radiation) enhanced the severity of genetically triggered eye disease.

The role of prostaglandins E2 and F2 alpha in ultraviolet radiation-induced cortical cataracts in vivo.

PURPOSE: Previous work has shown that exposure of lens epithelial cells or rabbit eyes in vivo to ultraviolet B (UVB) radiation enhanced prostaglandin (PG)E2 synthesis. Such enhanced PGE2 synthesis was related to the increased DNA synthesis that followed UVB exposure. The current study examined the relationship between enhanced prostaglandin synthesis and UVB-induced cataract formation. METHODS: Seventy albino (New Zealand white) rabbit eyes were exposed to UVB radiation in vivo. Fluence of radiation at the cornea was 2.8 J/cm2, 5.6 J/cm2, or 11.2 J/cm2. Eyes were examined 24 hours after UVB exposure and for as long as 10 days by slit lamp biomicroscopy. Mass spectrometry was used to measure PGE2, PGF2 alpha, and 6-keto-PGF1 alpha content of the lens and iris-ciliary body using authentic standards. To determine the effect of inhibition of prostaglandin synthesis on UVB-induced cataract formation, animals were given indomethacin intraperitoneally. Other pharmacologic agents, such as PGE2, PGF2 alpha, and misoprostol, were applied topically to the eye. The effect of UVB on K+ pump was determined by incubating isolated lenses with [86Rb+]. RESULTS: Twenty-four hours after UVB exposure, PGE2 and PGF2 alpha concentrations in aqueous humor were increased by 100- and 30-fold, respectively. Lens PGE2 and PGF2 alpha increased by 6- and 4-fold, respectively, after UVB radiation exposure. Pretreatment of animals with indomethacin prevented the rise in lens and aqueous humor PGE2 and PGF2 alpha levels. Furthermore, indomethacin was partially protective against UVB cataract formation and lowered cataract severity from stage 3 to stage 1, but it did not prevent UVB-induced lens changes completely. Topical application of PGE2 before UVB exposure completely prevented cataract formation in the UVB-exposed eye. In contrast, topical administration of PGF2 alpha increased cataract severity. UVB-induced cataract formation preceded changes in [86Rb]+ uptake in lenses subsequently incubated in K(+)-free Tyrode's. CONCLUSIONS: Enhanced synthesis of cyclooxygenase products of arachidonic acid metabolism in the lens is associated with UVB-induced cataract formation in albino rabbit eyes, and inhibition of cyclooxygenase by indomethacin decreased the severity of cataracts. PGE2, the principal arachidonic acid metabolite, appears to have a protective role because pretreatment of the eye with topical PGE2 completely prevented UVB-induced cataract formation, whereas PGF2 alpha increased the severity of the cataract. The evidence presented for a role of PGF2 alpha in the development of cataract suggests that caution be exercised in the use of PGF2 alpha derivatives in the therapy of glaucoma.

Experimental model of light focusing of the peripheral cornea.

PURPOSE: Epidemiologic studies have shown that the onset of cortical cataract occurs primarily in the inferonasal human lens and that the incidence of cortical cataract is correlated with ultraviolet light. Ray tracing analysis has suggested that the peripheral cornea concentrates light on the opposite peripheral lens and that the nose and orbit block peripheral light, except temporally, resulting in a relative concentration of light on the inferonasal lens. Studies were performed to test these theories. METHODS: A model cornea and anterior chamber, set on a disc of light-sensitive paper, was placed in the orbit of a human skull coated with wax to simulate soft tissue. The "eye" was exposed to summer sunlight at various times of day, with and without sunglasses. Discs from the different experimental groups were scanned, and the digitized images were analyzed densitometrically using image analysis software. RESULTS: With the head upright, the inferonasal section of the disc exhibited the most intense exposure under all lighting conditions. Sunglasses decreased the intensity of overall light exposure but did not eliminate the inferonasal bias. Only blocking the temple eliminated this effect. CONCLUSIONS: This model supports the idea that the peripheral cornea focuses light on the inferonasal portion of the human lens. These results may explain the correlation between light and the location of cortical cataract.

Cortical lenticular opacification: distribution and location in a longitudinal study.

PURPOSE: To examine the distribution of cortical opacification of the lens by lens quadrant in a longitudinal study. METHODS: In 1990, a follow-up assessment of a cohort of Chesapeake Bay watermen, initially studied in 1985, was performed. Four hundred thirty-seven subjects (834 eyes) had gradable cortical photographs for at least one eye in both 1985 and 1990. Cortical photographs were graded by both estimating total area and determining the quadrant with the greatest degree of cortical opacification. RESULTS: The prevalence and severity of cortical opacification increased with age with a high degree of concordance (84%) between eyes. For the 47 eyes with cortical opacification > or = 1/8 at baseline, the principal locations of opacification were: inferonasal 63.8%, inferotemporal 17.0%, superonasal 6.4%, and superotemporal 12.8% (P < 0.001, compared with equal distribution by quadrant). Five-year development of new cortical opacification and five-year progression of existing cortical opacification showed even greater preferential occurrence in the inferonasal quadrant of the lens. CONCLUSIONS: In this population, the inferonasal quadrant of the lens is the principal site of cortical opacification in both cross-sectional and longitudinal assessment. This finding is consistent with the hypothesis that sunlight exposure is a significant risk factor for cortical opacification.

UV-B and early cortical and nuclear changes in the human lens.

Experimental studies in mice and rats have shown that UV (B) irradiation leads to specific lens changes, viz. yellowing of the nucleus and a multilayered epithelium in the anterior pole with disrupted cortical fibres underneath. Biomicroscopic and ultrastructural studies on ageing human lenses revealed yellowing of the lens nucleus and locally ruptured membranes and small opacities in the equatorial cortex. No changes in the anterior pole were ever observed. This discrepancy between the human and animal lens, contraindicating UV as an important risk factor for human cataract, is discussed and may be due to several factors: (1) a difference between the high level acute and low level chronic irradiation; (2) species differences: nocturnal animals may be unable to cope with bright light exposure; (3) differences in scavenger and other defense mechanisms between humans and animals.

Election spin resonance studies of free radical formation and oxygen consumption of lens epithelium during ultraviolet exposure.

A long life election spin resonance (ESR) signal at g = 2.0006 was observed in the normal lens epithelium and cortical fibers. During ultraviolet (UV) exposure, a new ESR signal at g = 2.0060 was found in the lens epithelium. But this specific signal was not detected in the lens cortical fibers. This suggested that lens epithelial cells were more susceptible to the free radical formation which was induced by UV light. By means of ESR spin probe oximetry, the oxygen uptake of lens epithelial cells was measured. The more the oxygen uptake, the higher the K value was. The K value of the oxygen consumption of epithelial cell linearly correlated with time of consumption (20-60 min) and increased as a function of UV exposure time (1-5 min). The oxygen consumption rate of lens epithelial cell was approximately 1.38 x 10(6) and increased to 7.1 x 10(6) O2 molecules per cell per sec. The oxygen consumption rate increased more than 5 times. These results indicates that UV light can accelerate the respiratory function of lens epithelial cells. The necessity of excess oxygen of lens epithelial cells may play a role in the cataract formation induced by UV light.

The potential ocular phototoxicity of antidepressant drugs.

Light Therapy is a new treatment for patients with Seasonal Affective Disorder (SAD), a depressive state occurring during the winter as a result of decreased sunlight. The treatment involves placing the patient in front of a light box (2-10,000 lux) for approximately 30 min to 1 hour per day during the winter months. Although there have been no reports of damage to the eye from this treatment with light alone there is increased risk in light damage to the lens and retina if these depressed patients are being treated with antidepressant/neuroleptic drugs concurrently with their light therapy. As we have been previously reported certain drugs, having absorptions longer than 295 nm can act as photosensitizers resulting in enhanced light damage to the eye. Using a screening method developed by Roberts, we examined the potential phototoxicity of a variety of antidepressant and neuroleptic drugs.

Effect of chronic near-ultraviolet radiation on the gray squirrel lens in vivo.

The effects of ambient exposure to near-ultraviolet (near-UV) radiation (300-400 nm) on the ocular lens of the diurnal squirrel (Sciurus carolinensis) are reported. Gray squirrels lived in cages illuminated for 12 hr a day with near-UV light (6 mW/cm2, 365 nm) for 1 yr. The non-UV-exposed controls were housed separately. In the lenses of UV-exposed animals, anterior pole changes occurred. Central epithelial cells swelled, disappeared, or underwent proliferation. A band of disoriented degenerating fiber cells was seen in the midcortex, with a degree of liquefaction. When lens protein compartments were separated by centrifugation, water-insoluble but urea-soluble fractions were enhanced in the outer and inner cortex and the nucleus. Both high-performance liquid chromatography and polyacrylamide gel electrophoresis revealed that proteins mainly in the midcortex and nucleus were altered considerably. Evidence of a loss of sulfhydryl compounds (by chemical and Raman spectroscopic analyses) and an increase of protein-thiol mixed disulfides (chemically) was also observed. These data prove that repetitive ambient exposure of diurnal animals to near-UV radiation at subsolar levels damages the lens by interfering with the maintenance of epithelial cells and altering the structural proteins; some of this may be due to the conversion of sulfhydryls to mixed disulfides.

The effect of neodymium:YAG laser shocks on the blood-aqueous barrier.

An animal model demonstrates that the acute inflammation seen after neodymium: YAG (Nd:YAG) capsulotomy is related to the presence of disrupted tissue suspended in the aqueous, rather than to the mechanical insults by the repeated shock waves. Seven rabbits were treated in the lens cortex of one eye with 20 bursts of 4 pulses, 24 mJ each, and followed fluorophotometrically using albumin labelled with fluorescein. This allowed transmission of shock waves to the anterior segment without releasing debris in five eyes that showed no inflammation. Two eyes with inadvertent capsular rupture showed marked blood-aqueous barrier breakdown. This suggests the use of a capsulotomy technique that relies on discission rather than pulverization of the membrane and avoids the thicker portions of the membrane when possible.

Morphological and cell volume changes in the rat lens during the formation of radiation cataracts.

Earlier studies in our laboratory showed that 24 hr after X-irradiation, epithelial cells of early postnatal rat lenses increased in volume. Three days after X-irradiation, the underlying lens fibers increased in volume. This finding suggested a correlation between damage to epithelial cell volume regulation and subsequent fiber cell swelling. To test this hypothesis 4-week-old rat lenses were three-dimensionally reconstructed to determine average cell volumes of specific lens regions and wet weights of whole lenses were measured during radiation cataract formation. In addition, the differentiation of epithelial cells into lens fibers was monitored by autoradiography. Four-week-old Sprague-Dawley rats were injected with [3H]-thymidine and, 24 hr later, their eyes were irradiated with either 400 or 1200 rad. Lenses were examined with a slit lamp and cataracts were graded on a scale of 1+ to 4+. Animals were killed 24 hr and 3, 5, 15 and 30 weeks after exposure. Lenses were serially sectioned at 0.75 micron and epithelial, equatorial and cortical fiber cell volumes were determined. Rats exposed to 400 or 1200 rad developed 0.5-1.5+ or 2.5-3.0+ cataracts, respectively, 10-16 weeks after X-irradiation. Epithelial and equatorial cells of both groups did not significantly increase in volume during this period. Three weeks after irradiation with 1200 rad cortical fibers were disorganized and had increased volume. By 5 and 15 weeks, cortical fibers had more normal cell volumes, although their morphology remained grossly altered. Cortical fiber volume of lenses irradiated with 400 rad were not significantly different from control lenses throughout the experimental period. By 15 weeks lenses irradiated with 400 rad showed subtle changes in morphology. Wet weight determinations indicated that the localized increase in cortical fiber volume did not result in an increase in the wet weight of the entire lens. Autoradiography showed that affected fibers had been epithelial cells at the time of X-irradiation. These results provide additional evidence that disturbances in fiber differentiation are involved with cataract formation, but do not support the initial hypothesis that a disturbance in epithelial cell volume regulation leads to fiber cell swelling. Earlier results suggesting defects in lens epithelial volume regulation in radiation cataract formation may have been complicated by ocular inflammation.

Comparison of the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures.

We evaluated the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures. We produced corneal incisions, optical iridotomy, capsulotomy, and retinotomy with these lasers. Incisions produced with ArF showed sharply defined borders with minimal coagulative effects to the adjacent structures. Cuts created with KrF showed coagulative necrosis of the wound edges ranging from two to five um in width. From our study it appears that ArF has photoablative action and KrF has a predominantly photoablative action with minimal photocoagulative effect on the tissue.