Per G. Söderberg

An objective and rapid method for the determination of light dissemination in the lens

Abstract. A method for the objective measurement of light dissemination in the lens was developed. There is an exponential relationship between the concentration of standard solutions and the intensity of light disseminated forwards. The light disseminated in non‐pathological lenses from Sprague Dawley rats was registered as the equivalent standard concentration, C, and then transformed to log10 (C + 1) and was found not to deviate from the normal distribution. The tolerance limit for light dissemination was derived by setting the probability to classify a non‐pathological lens as pathological. An analysis of variance demonstrated that the inter‐animal variation was the dominating source of imprecision. It is anticipated that the developed system will be useful in experimental toxicological risk assessment.

Dose-response function for lens forward light scattering after in vivo exposure to ultraviolet radiation.

Abstractu2002· Background: It is known that different types of radiation, as well as aging and metabolic disorders, can cause cataract. Several epidemiological investigations show a correlation between cataract development and the dose of ultraviolet radiation (UVR) received. It is well established experimentally that exposure of animal eyes to UVR induces cataract. The purpose of the present study was to determine the dose-response function for UVR-induced opacities in the rat lens after in vivo exposure.u2002· Methods: Sprague-Dawley rats received 0.1, 0.4, 1.3, 3, 5, 8 or 14u2005kJ/m2 UVR (λMAX=300u2005nm, λ0.5=10u2005nm) unilaterally for 15u2005min. At 1 week after exposure both lenses were removed, photographs were taken and the intensity of forward-scattered light was measured.u2002· Results: One week after UVR exposure, opacities occurred on the lens surface, as observed with a microscope. With increased UVR dose the opacities became more intense and occurred also in the equatorial area of the lens, but not in the nucleus. The intensity of forward light scattering increased with increased UVR dose between 3 and 14 kJ/m2. No significant change in intensity of forward light scattering was observed for lower UVR doses. · Conclusion: The intensity of forward light scattering in the rat lens increases exponentially with increased UVR dose between 0.1 and 14u2005kJ/m2.

Long-Term Development of Lens Opacities after Exposure to Ultraviolet Radiation at 300 nm

The long-term development of lens opacities after short-term exposure to ultraviolet radiation (UVR) was determined. Altogether, 200 Sprague-Dawley rats received unilaterally 5 or 20 kJ/m2 UVR (lambda MAX = 300 nm, lambda 0.5 = 10 nm) in vivo, during 15 min. At 1, 4, 8, 16 and 32 weeks after exposure subgroups of 20 rats from each dose group were sacrificed. Both lenses were removed for measurement of intensity of forward scattered light. It was found that exposed lenses scatter light more than their contralaterals and that a higher dose induces more light scattering. After exposure to 5 kJ/m2, the mean difference in scattering remained unchanged between 1 and 32 weeks latency, but the distribution of the individual differences in scattering became skew. For several animals, lens opacities induced by 5 kJ/m2 seemed to decrease during the observation period. Earlier observations in complement to current findings implicate that it is optimal to detect close-to-threshold UVR-induced cataract at 1 week after exposure.

Vitamin E Can Protect against Ultraviolet Radiation-Induced Cataract in Albino Rats

Purpose: To investigate if vitamin E protects against ultraviolet B radiation (UVB)-induced cataract. Methods: Albino Sprague-Dawley rats were divided into two groups: one group was fed vitamin E, while the other group was used as a control. Both groups were exposed to UVB. The rats were sacrificed, lenses extracted, forward light scattering was measured, and vitamin E and glutathione (GSH) contents were determined. Results: Lenses in the vitamin E group developed slight opacities, while lenses in the control group developed nuclear cataracts. Forward light scattering in lenses of the control group was higher than in lenses in the vitamin-E-supplemented group. Vitamin E and GSH concentrations were higher in lenses treated with vitamin E than in the untreated group. Conclusions: Vitamin E protects the lens against UVB-induced cataract. Vitamin E protects directly as an antioxidant and/or indirectly through increased levels of GSH.

Cytochrome oxidase activity in rat retina after exposure to 404 nm blue light.

Cytochrome oxidase (CYO), a key enzyme in the respiratory chain, was observed as an indicator of retinal metabolism after an in vivo blue light exposure. Thirty Sprague-Dawley rats were exposed to optic radiation of 404 nm with a retinal dose of 110kJ/m2. Immediately after exposure, the CYO activity in the pigment epithelium, in the outer and inner segments of photoreceptors, and in the outer plexiform layer of the exposed retina, was reduced to one-third-to-half of the control level. However, there was an increase in CYO activity in the exposed retina one day after exposure. One week after exposure, the CYO activity in the inner segment and the outer plexiform layer was higher, while the activity in the other two layers was lower, than that at one day, although still higher than in the control. Two weeks after exposure, the CYO activity in the four retinal layers returned to the level of the control retina, as did the activity four weeks after. After exposure, no ophthalmoscopically visible retinal change and no light-microscopically evident morphological alterations were found. There was no retinal edema or loss of photoreceptor cells. The observed alteration in CYO activity after blue light exposure may represent an inhibition of retinal metabolism. The inhibition was reversible. If this compensation mechanism is overwhelmed, retinal damage may occur.

Development of light dissemination in the rat lens after in vivo exposure to radiation in the 300-nm wavelength region.

The course of development of light dissemination was investigated for rat lenses exposed in vivo to 30 kJ/m2 ultraviolet radiation (UVR) in the 300-nm wavelength region. After an initial latency phase the light dissemination increases rapidly. At 72 h after the exposure to UVR, light dissemination almost reaches a maximum. An exponential model is proposed for the analysis of this pattern. Light dissemination also increases in lenses contralateral to exposed. This indicates that there may be a systemic response after exposure to UVR which can lead to cataract formation.

Unscheduled DNA synthesis in lens epithelium after in vivo exposure to UV radiation in the 300 nm wavelength region

Abstract A quantitative autoradiographic method was developed to study the pattern of DNA synthesis in the rat lens epithelium after in vivo exposure to UV radiation in the 300 nm wavelength region. It was found that UV radiation (peak transmission = 298 nm, half‐width = ± 10 nm) induces unscheduled DNA synthesis and that the proportion of nuclei in S‐phase concurrently is reduced indicating an inhibition of the scheduled DNA synthesis. The registered unscheduled DNA synthesis is believed to be excision repair of DNA damage induced by the UV radiation. Excision repair in lens epithelial cells could be one mechanism involved in the correlation between exposure to sunlight and cataracts.

Universal Opacity Standard for Scheimpflug Photography

Purpose: To develop a universal standard for comparison of the results from different studies using Scheimpflug photography. Material and Method: A suspension including polystyrene spheres was selected as the universal standard. The polystyrene suspension was diluted into 10 concentrations by adding spectroscopic quality water. An artificial eye chamber was designed to hold the diluted suspension for photography. Each concentration was photographed by both a Topcon SL-45 slit-lamp camera and a Nidek EAS-1000 system. The intensity of back-scattered light was analyzed statistically. Results: The relationship between the concentration of the polystyrene suspension and the internal gray scale step within the Topcon SL-45 camera can be described by a second-order polynomial. The relationship between the concentration of the polystyrene suspension and the measurement of the Nidek EAS-1000 system can also be expressed by a second-order polynomial. The relationship between the Topcon SL-45 camera and the Nidek EAS-1000 system is linear. Conclusions: The results of lens nuclear opacity measured with different Scheimpflug cameras can be compared using the method established in the study. The linear relationship between the Topcon SL-45 and Nidek EAS-1000 systems can be used to convert measurements from one system to the other.

Failure of ascorbate to protect against broadband blue light-induced retinal damage in rat.

Abstractu2002· Background: Excessive generation of free radicals due to light absorption is proposed as the most likely mechanism for photochemical retinal damage. The observed reduction of green light-induced retinal injury after ascorbate treatment is believed to be an antioxidative effect. The aim of the present study was to evaluate the possible protection of ascorbate against blue light-induced photoreceptor damage. · Methods: Cyclic light-reared albino rats were injected intraperitoneally with either ascorbate (1 mg/g body weight) or, as placebo, physiological saline 24 h before and just prior to exposure to blue light. After 20–22 h of dark adaptation, two groups of the rats were exposed in pairs to the blue light (400–480 nm) for 6 h at an average irradiance of 0.7 W/m2 in the cage. Six days after light exposure, all rats were killed and retinal samples were analyzed. · Results: Diffuse blue light irradiation resulted in an uneven distribution of damage in the retina. As judged from the pathological changes in the retina irradiated, no microscopic difference was observed between the two groups. The preserved thickness of the outer nuclear layer was on average 61.3% in the ascorbate-treated and 66.4% in the placebo-treated group. The photoreceptor loss was not significantly different between the two groups. · Conclusion: The ascorbate did not protect the retina from blue-light induced damage. This favors the assumption that the mechanisms for blue light-induced retinal damage might differ from that for green light.

Inactivation of lactate dehydrogenase by UV radiation in the 300 nm wavelength region.

SummaryThe effect of UV radiation on lactate dehydrogenase (LDH) was investigated. LDH from bovine heart was exposed to 3.6–18 kJ/m2 of ultraviolet (UV) radiation in the 300 nm wavelength region. The activity of LDH was observed to decrease as a function of the dosage of UV radiation. The inactivation of LDH was independent of exposure rate at constant dosage of UV radiation. The decrease of LDH activity caused by UV 300 nm radiation was coupled to a decrease of the maximal velocity (Vmax) while the Michaelis constant (Km) remained unchanged. The absorption spectrum of the LDH changed during exposure to UV radiation suggesting an alteration of tryptophan in the LDH molecule.