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.

Effect of ultraviolet radiation on the energy metabolism of the corneal epithelium of the rabbit

The present research was directed at quantifying possible alterations in corneal epithelial metabolic activity secondary to in vivo exposure to ultraviolet radiation (UVR). Microfluorometric energy metabolite assays on microgram (microgram) sized, freeze-dried tissue samples were used as an in vitro means of assessing overall metabolic activity in the epithelium of control rabbit corneas and in the epithelium of UVR-exposed rabbit corneas 2 min after discontinuation of exposure. The specific assays were for glucose, glycogen, adenosine triphosphate (ATP), and phosphocreatine (PCr). The radiant exposures were kept constant at 0.05 J cm-2 for all UVR wavelengths utilized (290, 300, 310 and 360 nm). Experimental UVR exposure conditions served to increase epithelial glucose and glycogen concentrations. Although the epithelial ATP concentrations were unchanged, the epithelial PCr concentrations (a high energy phosphate bond reservoir) decreased as a result of UVR exposure. Overall, the data demonstrate a decrease in corneal epithelial metabolic activity, which may be wavelength-dependent, as a result of UVR exposure. It is suggested that immediate metabolic stress can be responsible for the pattern of epithelial cell loss seen in photokeratitis.

Changes in the rabbit corneal stroma caused by UV-radiation

Three days after UV-irradiation of the rabbit cornea, there was epithelial loss and stromal oedema, which was most prominent in the anterior 1/4. Many of the keratocytes in this region were killed. The inner 3/4 of the stroma showed a large number of round or oval cells with nuclear fragmentation and abnormal inclusions. These cells were taken to be seriously, though reversibly harmed keratocytes. The tissue structure was normalized within one week, and the UV-induced changes seem to refer to the 290-350 nm interval.

Alterations to eye structures in hairless mice by long-term ultraviolet irradiation. A histopathological study

The eyes of 75 Hr/Hr hairless mice were irradiated with one minimal erythema dose/day of UV light for a period of 12 months, and then observed for a further 6 months. The mice were divide into 3 subgroups, - one without protectans, - one protected by the sun protection lotion Sea and Ski, factor 5, - and one by Piz Buin, Factor 6. The eyes of 75 non-irradiated mice of the same type, subdivided into 3 comparable groups, served as controls. Animals which died during the test period were examined immediately. After the 18 months period, eyes and adnexa of the surviving animals were examined macroscopically and by light microscopy. The lifespan of unprotected, irradiated mice was significantly shorter than the protected groups. The eyelids of irradiated mice presented hyperplasia, actinic keratosis and invasive carcinoma, the latter in 20%. No melanotic tumours were recorded. Since the sun lotion protected animals had a significantly longer lifespan they showed a higher number of palpebral tumours. No irradiation lesions could be demonstrated in the lens, the vitreous or the retina.