Ultra-violet radiation as a possible cause of corneal degenerative changes under certain physiographic conditions

Climatic Droplet Keratopathy Is a Misnomer for This Corneal Degeneration

PURPOSE

To describe a new insight into the Climate Droplet Keratopathy (CDK) pathophysiology and its major predisposing factors.

METHOD

A literature search was undertaken on PubMed to compile papers published on CDK. The following is a focused opinion tempered by synthesis of current evidence, and research of the authors.

RESULTS

CDK is a multifactorial rural disease common in regions with high incidence of pterygium, but not related to the type of climate or ozone concentrations. Although it has been thought that climate is the cause of this disease, recent investigations deny that and reveal that other environmental factors such as dietary intake, eye protection, oxidative stress, and ocular inflammatory pathways play an important role in the pathogenesis of CDK.

CONCLUSION

Considering the negligible effect of climate, the present name " CDK" for this illness can be confusing for young ophthalmologists. Based on these remarks, it is imperative to start using an accurate name like "Environmental Corneal Degeneration (ECD)" that fits the most recent evidence related to its etiology.

Climatic Droplet Keratopathy in Argentina: Involvement of Environmental Agents in Its Genesis Which Would Open the Prospect for New Therapeutic Interventions

Climatic droplet keratopathy (CDK) is a degenerative corneal disease of unknown etiology. We described CDK for the first time in Latin America in the Argentinean Patagonia (El Cuy). A deeper knowledge of CDK pathogenic mechanisms will provide new therapeutic strategies. For that reason we investigated the prevalence of CDK in El Cuy and its existence in other 3 provinces with similar climate. Patients eyes were examined, habits throughout lives were inquired about, and serum ascorbate (sAA) was determined. All individuals work outdoors for most of the day. All regions had normal O₃ levels. Individuals from regions 1, 2, and 3 had very low consumption of vegetables/fruits and low sAA levels. Conversely, region 4 individuals had balanced diet and higher sAA concentrations. CDK was only found in region 3 where individuals had partial deficiency of sAA and did not use eye protection. No CDK was found in regions 1 and 2 where individuals had similar work activities and dietary habits to those in region 3 but wear eye protection. No disease was found in region 4 where individuals work outdoors, have balanced diet, and use eye protection. To summarize, the CDK existence was related not only to climate but also to the dietary habits and lack of protection from sunlight.

Genetic background and climatic droplet keratopathy incidence in a Mapuche population from Argentina

Purpose

To determine whether the incidence of and susceptibility to climatic droplet keratopathy (CDK), an acquired, often bilateral degenerative corneal disease, is influenced by the genetic background of the individuals who exhibit the disorder.

Methods

To determine whether the disease expression was influenced by the genetic ancestry of CDK cases in native Mapuche of the northwest area of Patagonia in Argentina, we examined mitochondrial DNA and Y-chromosome variation in 53 unrelated individuals. Twenty-nine of them were part of the CDK (patient) population, while 24 were part of the control group. The analysis revealed the maternal and paternal lineages that were present in the two study groups.

Results

This analysis demonstrated that nearly all persons had a Native American mtDNA background, whereas 50% of the CDK group and 37% of the control group had Native American paternal ancestry, respectively. There was no significant difference in the frequencies of mtDNA haplogroups between the CDK patient and control groups. Although the Y-chromosome data revealed differences in specific haplogroup frequencies between these two groups, there was no statistically significant relationship between individual paternal genetic backgrounds and the incidence or stage of disease.

Conclusions

These results indicate a lack of correlation between genetic ancestry as represented by haploid genetic systems and the incidence of CDK in Mapuche populations. In addition, the mtDNA appears to play less of a role in CDK expression than for other complex diseases linked to bioenergetic processes. However, further analysis of the mtDNA genome sequence and other genes involved in corneal function may reveal the more precise role that mitochondria play in the expression of CDK.

Altered expression of matrix metalloproteinases and their tissue inhibitors as possible contributors to corneal droplet formation in climatic droplet keratopathy

PURPOSE

Climatic droplet keratopathy (CDK) is an acquired corneal disease characterized by progressive scarring of the cornea. In several corneal diseases, matrix metalloproteinases (MMPs) are upregulated during the degradation of epithelial and stromal tissues. We investigated the levels, degree of activation and molecular forms of MMP-2, MMP-9, MMP-8 and MMP-13 and their tissue inhibitors TIMP-1 and TIMP-2 in tear fluid of patients with CDK.

METHODS

Seventeen CDK patients and 10 controls living in Argentine Patagonia received a complete eye examination, and MMPs and TIMP-1/2 were determined by immunofluorometric assay (IFMA), gelatin zymography and quantitative Western immunoblot analysis in tear samples.

RESULTS

The MMPs were detected mostly in their latent forms. The levels of MMP-9 and MMP-2 were found to be significantly elevated in CDK patients, whereas latent and active MMP-8 levels were significantly enhanced in controls. There was no significant difference in the level of MMP-13. TIMPs were found as part of complexes, and the TIMP-1 levels were significantly lower in patients than controls.

CONCLUSION

Elevated MMP-2 and MMP-9 levels have been implicated in the failure of corneal re-epithelialization, and enhanced MMP-2 and MMP-9 levels in CDK patients suggest that these MMPs may play a role in corneal scarring in CDK. Elevated levels of MMP-8 suggest a defensive role for this MMP in inflammatory reactions associated with recurring corneal traumas. Decreased expression of TIMP-1 in CDK patients suggest deficient antiproteolytic shield likely to render the corneas of CDK patients vulnerable to enhanced MMPs. Overall, these data suggest a mechanistic link between MMPs and TIMP-1 level in cornea and tears with corneal scarring in CDK.

Surface Alterations, Corneal Hypoesthesia, and Iris Atrophy in Patients With Climatic Droplet Keratopathy

PURPOSE

To present external eye findings and the observation of iris atrophy in patients with climatic droplet keratopathy (CDK).

METHODS

Twenty-three patients with CDK and 13 controls living in a semideserted plain of the Argentine Patagonia were studied. Besides a comprehensive eye examination, Cochet-Bonnet aesthesiometry, Schirmer II test, breakup time (BUT), and surface staining were performed. According to corneal findings, eyes were grouped as grade 1 (confluent translucent microdroplets localized in the limbic region of the horizontal quadrants); grade 2 (band-shaped subepithelial haziness compromising the central cornea); and grade 3 (previously described lesions with yellow subepithelial droplets). Results were analyzed with the Fisher, Mann-Whitney, and Spearman tests, which were considered significant at P < 0.05.

RESULTS

Nineteen of 23 patients with CDK had bilateral disease, which was asymmetric in 2 of them. Sixteen eyes had grade 1, 21 eyes had grade 2, and 5 eyes had grade 3 disease. Aesthesiometry showed that the more advanced the disease, the more profound the corneal hypoesthesia (P = 0.0008). BUT and ocular surface staining significantly differed between eyes with grade 3 and grade 1, grade 3 and grade 2, and grade 3 and controls. In 38.09% of eyes with CDK and in none of the controls, sectorial depigmentation and atrophy of the inferior iris were observed.

CONCLUSIONS

A severe decrease of corneal sensitivity was observed in advanced stages of CDK. Some degree of dry eye was present in most patients, but severe disease was infrequent at any stage of CDK. Inferior iris depigmentation and atrophy was frequently observed among patients with CDK.

Climatic droplet keratopathy in the Argentine Patagonia

PURPOSE

To present the findings of climatic droplet keratopathy (CDK) that affects people of a rural area of the Argentine Patagonia.

DESIGN

Observational case series.

METHODS

Five hundred seventy-seven individuals who live in settlements and villages in an inland area of the northwest Patagonia region in Argentina received a complete eye examination.

RESULTS

The mean age was 36.02 years (r = 1.5 months to 89 years); 55.63% of the patients were female. The mean age of the 7.62% of the patients who had typical CDK was 65.31 years (r = 42 to 89 years); 86.36% of the patients were male. Of 66 eyes in 35 patients with CDK, 35 eyes had peripheral haziness (grade 1); 23 eyes had a band-shaped haziness (grade 2), and 8 eyes had the aggregate of yellow subepithelial droplets (grade 3). Pinguecula, pterygium, cataract, and pseudoexfoliation were frequent findings among patients with CDK.

CONCLUSION

CDK is not infrequent among male adults in this area of the Argentine Patagonia and may be severely handicapping.

Spheroidal Degeneration of the Cornea

PURPOSE

To describe a case with clinicopathologic findings of spheroidal degeneration of the cornea in a 78-year-old man.

METHODS

Description of the clinical features of 1 bilateral case with histopathologic findings from the penetrating keratoplasty specimen.

RESULTS

Spheroidal degeneration of the cornea with histopathologic confirmation of extensive elastotic degeneration in anterior corneal stroma.

CONCLUSIONS

The spheroidal degeneration in this patient was of visual significance. The history of repeated, extreme ultraviolet exposure during arc welding is believed to be the proximal cause of these corneal changes.

Serious occurrences in the natural history of advanced climatic keratopathy

BACKGROUND

Climatic or chronic actinic keratopathy is an important corneal degeneration occurring after prolonged climatic exposure. The advanced stages of disease are confined generally to tropical or arid localities (including the Arctic) with high levels of sunlight. After many years of disease evolution, the advent of stage 3 keratopathy often presages a rapid downhill course. The instability of advanced climatic keratopathy has received little attention.

METHODS

Eighteen patients with advanced climatic keratopathy are described from the Transvaal region in South Africa and from Saudi Arabia. Patients with rapid disease progression, spontaneous sterile ulceration, and secondary microbial keratitis are described.

RESULTS

The rapid progression characteristic of stage 3 climatic keratopathy is illustrated. Severe, focal, sterile ulceration of the devitalized corneal degeneration may be common. Secondary infection may occur, leading to rapid dissolution of the climatic keratopathy material. Corneal perforation may ensue. The occurrence of yellow or brown fragments of the climatic keratopathy within or adjacent to the corneal inflammatory infiltrate indicates the predisposing cause of the infection, as usually also with examination of the opposite eye.

CONCLUSIONS

These observations emphasize the inherent instability of advanced climatic keratopathy, which frequently takes a relentless downhill course. In rural populations of the developing world, climatic keratopathy is an important cause of blindness. Disease pathogenesis, treatment, and prevention deserve greater study.

Early cell kinetic effects of a single dose of narrow-banded ultraviolet B irradiation on the rat corneal epithelium

The right eyes of 40 rats were exposed to a single erythemogenic dose of ultraviolet B irradiation (UVB) at 297 nm. The irradiation was directed perpendicular to the center of the cornea. The left eyes served as controls. The animals were randomly assigned into 10 groups. The labeling index (LI) after pulse labeling with tritiated thymidine and the mitotic rate (MR) after Colcemid administration were registered in the corneal epithelium at predetermined intervals up to 96 h after the irradiation. A mathematical method was used to correlate corresponding corneal areas from the different animals. In the central cornea the LI was considerably reduced up to 36 h after the irradiation. The LI increased toward the peripheral cornea and reached normal values at the limbal area. The MR was also reduced up to 36 h. However, this reduction was over the entire epithelium. The block in cell proliferation was followed by increased proliferation.

The release of a neutrophil chemotactic factor from UV-B irradiated rabbit corneas in vitro

Rabbit corneas were isolated, mounted on plastic rings to form a cup and the endothelium was covered with RPMI tissue culture medium. The preparation was then irradiated with 1 J. cm-2 of 300 nm light over 1 hour and then incubated for a further two hours in the dark. The supernatant fluid was assayed for chemotactic activity toward rabbit neutrophils in an in vitro Boyden chamber assay. The results indicated that medium from irradiated corneas had a chemotactic activity that was 42% of that produced by the standard chemoattractant f-met-leu-phe, (10(-9) M) while medium from unexposed corneas and exposed medium alone had less than 3% activity. An in vivo assay using sub-epidermal injection into the back of a rabbit gave qualitatively similar results, only f-met-leu-phe and the medium from irradiated corneas causing neutrophil infiltration of the tissue. A checkerboard analysis confirmed that the activity was chemotactic rather than chemokinetic. Release of a chemotactic factor following UV-B irradiation provides a mechanism for the recruitment of neutrophils, at specific localized areas of the endothelium, that is seen after discrete in vivo irradiation. The results also confirm the importance of corneal inflammatory mediators in the development of tissue damage subsequent to exposure to toxic agents.

Alterations of the anterior lens capsule associated with climatic keratopathy

We describe changes in the anterior lens capsules of older people in Somalia, a country which is close to the equator and with large areas of sand, often highly reflective of sunlight. The capsule changes are confined to the central pupillary area. In order of apparently increasing severity they consist of a white opalescence ('frosting'), an elevation in front of the contour of the rest of the lens to form a plateau, and a 'bag' or herniation of the lens capsule through the pupil. Plateau and bagging taken together are strongly associated with climatic keratopathy (and by inference with reflected ultraviolet exposure), weakly associated with exfoliation syndrome, inversely related to the degree of cataract, and interfere severely with vision.

Long-term effects of a single dose of ultraviolet-B on albino rabbit cornea--I. in vivo analyses

Both eyes of female albino rabbits (1.9 kg) were exposed to a single dose of UV-B (300 +/- 9 nm; 0.125 J/cm2 total dose) between 13.30 and 15.00 h. The average irradiance was 209 +/- 4 microW/cm2 delivered over 612 +/- 13 s. At various time periods thereafter (every 12 h for 3 days, 6, 7, 14, 28, 42, 56, 112, 224 and 336 days post-irradiation), the animals were subjected to a full slit lamp examination to evaluate the status of the cornea and the anterior segment along with optical or ultrasonic pachometry of central corneal thickness. The results were compared with studies on age-matched rabbits over the same time period. In response to the UV-B irradiation, the corneas showed a modest edema (20% increase in central corneal thickness) that peaked at 48 h. Nearly normal central corneal thickness returned in 6 days and followed by a secondary very slight swelling (less than 5%) that resolved by 14 days. The edema was accompanied by keratitis over the same period. Thereafter, both control and UV-B irradiated corneas progressively increased in thickness with age. Biomicroscopy also revealed the appearance of granular opacities in the corneal epithelium that peaked at 72-96 h and resolved over 28 days. In addition, very small microdot opacities of the corneal epithelium were present in the UV-B irradiated corneas that reached maximum at 72 h but persisted to some degree throughout the evaluation period. Biomicroscopy also revealed a progressive disruption of the homogeneous nature of the corneal stroma by the appearance of large 'bread crumb'-like opacities that started at 72 h and was still present at the end of the evaluation period. These results suggest that long-term evaluation of the cornea is important after acute UV-B exposure and indicate that acute exposure to UV-R can produce corneal changes resembling those reported following chronic exposure to UV-R-rich environments.

The effects of UV-B irradiation on the corneal endothelium

Rabbit eyes, in vivo and in vitro, were exposed to UV-B irradiation at 300 nm, from a mercury arc lamp with an 11 nm bandpass filter. Radiant exposure ranged from 0.1 J/cm2 to 0.5 J/cm2. In vivo, swelling of the cornea resulted over a 12 to 40 hr period, the extent and duration being directly related to exposure. Recovery of normal thickness was complete within four days. Corneas removed at 18 hr after exposure recovered normal thickness during a five hour perfusion period, except for those most heavily exposed. When removed at 42 hr post exposure all corneas thinned to almost normal thickness. SEM showed the endothelial cells of exposed eyes to have either exaggerated villi on the surface and a disorganized mosaic or, after higher exposures, to be devoid of villi and have loose, flap like cell borders and large "blebs." After exposure of isolated corneas mounted for perfusion, swelling again ensued and similar changes were observed in the appearance of the cells, except that "blebs" were not found. No significant changes were observed in the metabolic components ATP, ascorbate and glutathione, nor was there any indication of lipid peroxidation. At higher in vivo exposures, the aqueous humor did show a decrease in ascorbate concentration and an increase in protein content, which probably result from a breakdown of the blood-aqueous barrier. UV-B irradiation may cause or promote changes in the endothelium associated with aging, but the one time radiant exposures of the magnitude used in this study, appear to have no severe or permanently toxic effects.

Climatic droplet keratopathy and pterygium

The association of various personal, occupational and environmental factors with climatic droplet keratopathy and pterygium was examined in a group of Australian Aborigines. Climatic droplet keratopathy was seen especially in aboriginal males who had worked as stockmen for more than 20 years. Although no definite association with a single causal factor could be made, there is circumstantial evidence for the importance of ultraviolet radiation. Pterygium was more commonly seen in those who worked outside, and it was positively correlated with lower latitudes and high ultraviolet levels.

Aetiology of spheroidal degeneration of the cornea in Labrador

To determine the aetiology of spheroidal degeneration of the cornea (Labrador keratopathy), total population surveys were conducted in 5 communities in coastal Labrador and northern Newfoundland. For 4 years records were also kept on all clinic patients aged 40 or more throughout the region. Both methods gave a peak prevalence at latitudes 55 degrees--56 degrees north. The greatest severity and earliest age of onset occurred around the same latitudes. Of the proposed environmental causative agents only ultraviolet radiation, reflected from ice and snow, explains the distribution of the disease. The high cumulative UV dosage is due to the unique geographical and climatic features of the region.

Aetiology of climatic droplet keratopathy and pterygium

The association of various personal, occupational, and environmental factors with climatic droplet keratopathy and pterygium was examined in a group of Australian Aborigines. Climatic droplet keratopathy was seen especially in aboriginal males who had worked as stockmen for more than 20 years. Although no definite association with a single causal factor could be made, there is circumstantial evidence for the importance of ultraviolet radiation. Pterygium was more commonly seen in those who worked outside, and it was positively correlated with lower latitudes and high ultraviolet levels.