Garźon-Chavez, Daniel R., Quentin, Emmanuelle, Harrison, Simone L., Parisi, Alfio V., Butler, Harry J., and Downs, Nathan J. (2018) The geospatial relationship of pterygium and senile cataract to ambient solar ultraviolet in tropical Ecuador. Photochemical & Photobiological Sciences, 17 (8). pp. 175-1083.

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Abstract

Tropical Ecuador presents a unique climate in which to study the relationship between ambient levels of solar ultraviolet radiation and eye disease in the absence of a latitudinal gradient. The national distribution of surface ultraviolet, taking into account MODIS and OMI satellite observation of aerosol, ozone, surface albedo, local elevation and cloud fraction measured during 2011 were compared to national pterygium (WHO ICD H11) and senile cataract (WHO ICD H25) incidence projected from the 2010 National Institute of Statistics and Census (Ecuador). Public Health Ministry projections for age categories 0 to 39, 40 to 59 and 60+ years were compared to surface ultraviolet irradiance data in 1040 parishes. Correlations drawn between modelled surface ultraviolet and eye disease incidence show a significant increase in both pterygium and senile cataract for the highest ambient exposure regions of the Pacific coast and western lowlands with incidence rates of 34.39 and 16.17 per 100 000 residents respectively. Lowest rates of incidence for pterygium (6.89 per 100 000) and senile cataract (2.90 per 100 000) were determined in high altitude sites and are attributed here to increased daily cloud fraction for parishes located in the Andean mountain range. The South American Andes experience the highest solar UV exposures on earth and report frequent high incidence of keratinocyte cancer. Our results show the high Andes to be the location of lowest eye disease incidence suggesting that both pterygium and senile cataract are the result of cumulative exposure to solar ultraviolet. These findings have clear implications for the agricultural workers and fishermen of the lowland districts of Ecuador, contrary to conventional understanding that greater risks are faced in locations of high altitude.

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