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P.S. Lee, C. Bunce, J.L. Y. Yip, P.J. Foster, B.L. Diffey, G.J. Johnson; Relative Ocular Solar Ultraviolet Light Exposure in Mongolian Outdoor Workers . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4487.
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© ARVO (1962-2015); The Authors (2016-present)
To measure the relative ocular ultraviolet (UV) exposure as determined by the Ocular Ambient Exposure Ratio (OAER) of solar UV light in Mongolian outdoor workers.
A novel electronic UV measuring device mounted on a headband was used to estimate the amount of UV–B reaching the human eye. The device consists of 2 UV sensors which were connected to a voltage amplifier that was connected to a data logger. Two sensors were positioned close to the left lower eyelid (sensor1) and adjacent to the temporal aspect of the right eye (sensor2). This allowed both incident and reflected solar UV to be recorded. Ambient UV was measured using a Robertson–Berger Biometer. Ambient UV levels and ocular surface UV were recorded simultaneously, together with time of readings, to allow the calculation of the ratio of ambient UV reaching the eyes relative to ambient UV (OAER). 20 different Mongolian outdoor workers wore the headband–mounted device for one day each while performing their normal activities. They kept a diary of their activities and of the weather conditions for each hour .
Ambient UV levels increased from the lowest mean minimal erythema dose (mMED) of 0.76 (95%CI: 0.63–0.88) at 0830 to a maximum mMED of 2.83 (95%CI: 2.15–3.50) at 1330. Conversely, lowest mean ocular surface UV levels occured at 0830 with a mMED of 0.24 (95%CI: 0.08–0.40) to a maximum of 0.61 (95%CI: 0.22–1.43) at 1330. However, mean OAER was highest in the morning (0.49, 95%CI: 0.38–0.60 at 0930) and decreased throughout the day, with an OAER of 0.29 (95%CI: 0.19–0.39) at 1330 to a minimum of 0.04 (95%CI: <0–0.10) at 1900. 17 out of 20 subjects were shaded during lunch hours where the sun was at its highest.
The highest OAER occured in the morning, although ambient UV levels were low. This may be due to behavioural factors; individuals may turn towards the sun during cold mornings for warmth. Prolonged exposure at lower levels of ambient UV, but with a higher OAER may be more damaging to the eye, especially as most participants were shaded during hours of peak ambient UV levels. Climatic conditions and behavioral factors played an important role in determining ocular UV exposure, the main causative agent in climatic droplet keratopathy, which is a major source of ocular morbidity in Mongolia.
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