Climate Change and the Eye

Climate change may directly alter global ocular disease patterns, but the societal effects of extreme weather and rising sea levels will have the most devastating impact on ocular health, according to Professor Robert J Casson MB.

“The direct effects of climate change on ocular health will be relatively minor and remain largely speculative,” he said. “Nevertheless, the indirect effects are likely to be catastrophic.”

The scientific community has been aware of global warming since 1859 when John Tyndall began the discussion of climate change resulting from greenhouse gases in the atmosphere, and later Svante Arrhenius, who described the effect of carbon dioxide on the earth’s surface temperature in 1896. Its anthropogenic nature likewise became clear during the 20th century.

The world has been getting warmer since accurate measures began—and increasingly so in recent decades. In the early years of the current century, Frank Luntz, an American Republican party political propagandist, popularised the term “climate change” because he said “global warming” sounded too scary.

“Luntz was right about one thing,” Prof Casson said. “That global warming is scary. In fact, the World Health Organization has described global warming as the single biggest health threat facing humanity.”

An evaluation of climate change’s threat to ocular health requires consideration of both the direct and indirect effects of global warming, he noted. Direct effects might include some temperature-dependent or seasonal pathogenic component, such as seasonal allergic conjunctivitis or posterior vitreous detachment and associated retinal detachment, where dehydration is a risk factor.

A rise in world temperature will lead to people spending more time outdoors, Prof Casson posited, resulting in increased exposure to ultraviolet light that could raise the incidence of cortical cataract. More outdoor activity might also lead to a reduction in myopia.

Changes in vector-borne diseases are amongst the direct effects of climate change. There is already considerable evidence that climate change is altering the seasonal distribution of disease vectors, such as flies carrying trachoma and mosquitoes carrying malaria and dengue. However, malaria’s spread will probably have negligible impact on global eye health because its ocular complications are rare.

The indirect effects of global warming on ocular health will most likely result from extreme weather events and rising sea levels that will create a catastrophic and worsening cycle of water shortages, food shortages, natural diseases, and poverty. Research has shown a strong association between poverty and visual impairment. Below an income threshold of 10,000 USD per capita, Prof Casson said, the prevalence of blindness increases.

“Two-hundred years ago, 90% of the world’s population was in abject poverty. Now that figure is around 10%. Alleviating that last 10% will be a challenge,” he concluded. “But of all things, it is likely to have the most profound effect on reducing the prevalence of visual impairment. However, in the presence of climate change, we may see an unravelling of all that good work and a reversal of the trend of poverty reduction and age-related visual impairment.”

Prof Casson spoke at the virtual 2022 World Ophthalmology Congress.

Robert J Casson MB.BS (Hons), MBiostats, DPhil, FRANZCO is Professor of Ophthalmology at the University of Adelaide and Vice Chair of Sight for All, North Adelaide, South Australia, Australia. robert.casson@adelaide.edu.au

Tags: sustainability