Glaucoma more common in people with lower income

People in the United Kingdom who have less income are more likely to suffer from glaucoma, researchers say.

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Since the national healthcare system provides most care at little or no charge, socioeconomic status must interact with patients’ health in some other way, say the researchers from the United Kingdom, Singapore and Australia.

The article appeared August 28 in the journal Eye (http://www.nature.com/eye/journal/vaop/ncurrent/full/eye2015157a.html).

Although previous studies have shown a correlation between a high glaucoma prevalence and low socioeconomic status, this is the first study to show that glaucoma prevalence decreases across the spectrum as income rises, the researchers write.

The researchers analyzed data from UK Biobank which tracks 502,656 participants between 40 and 69 years of age. Adequate information on visual acuity, autorefraction, keratometry, interaocular pressure, and corneal biomechanics were available on a subset of 112,690.

Of these, 1916 (1.7%) reported a diagnosis of glaucoma. The frequency of self-reported glaucoma was significantly higher amongst Asians (2.1%) and Blacks (3.3%). However, there was no significant difference in the rate between Chinese and White participants, or between mixed and other ethnicities and White participants.

The researchers also found a correlation between annual household income and glaucoma. Rates of glaucoma were highest among those with the lowest income and decreased as income increased.

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Among those making less than £18 000 the rate was 2.4%, whilst among those with an income of greater than £100 000, the rate was 0.9%. The difference was statistically significant, (P < 0.001).

The researchers delved deeper into the question of socioeconomics by comparing glaucoma rates to the Townsend deprivation index, which takes into account such factors as unemployment, non-car ownership, non-home ownership, and household overcrowding. The average United Kingdom score is 0, and a more positive score equals more deprivation.

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By this measure, both those with glaucoma and those without were less deprived than the average person in the United Kingdom.

But greater deprivation correlated with more glaucoma. Those with glaucoma had a mean Townsend score of -.72 whilst those without glaucoma had a mean Townsend score of -.95.

The findings fit into patterns found in previous research. Other studies have revealed a higher rate of glaucoma in the lowest end of the socioeconomic spectrum, for example among the homeless and the poor in Los Angeles.

Previous research has also shown that people of lower socioeconomic status in the United Kingdom are more likely to seek treatment when the condition is advanced. This is true of people who come from underprivileged areas, are of ‘lower occupational class,’ don’t have access to a car, have left full time education at age 14 years or younger, and are tenants rather than owners of their homes, the researchers write.

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In Canada, too, researchers found an association between living in poorer neighborhoods and presenting for treatment with more advanced glaucoma.

And previous research also supports the theory that later presentation is related to deprivation. A geographical mapping study showed that areas of the most deprivation were farthest from optometric services.

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Likewise, a study in Pakistan showed that cataract surgical coverage, intraocular lens implantation and spectacle coverage was higher in more affluent areas than in poorer areas.

The present study adds to these findings by showing that glaucoma prevalence decreases across the spectrum of income levels as income rises, the researchers say. They did not find a threshold at which deprivation takes effect.

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The finding also fits into a similar pattern of decreasing risk with rising income for all cause mortality, coronary heart disease mortality and vascular mortality.

Authors of these previous studies commented that these associations seemed to stem largely, though not entirely, from health-related behaviors such as physical activity, smoking and consumption of fruits, vegetables and alcohol.

Although the National Health Service provides eye care at little cost, people of lower socioeconomic status may run into other barriers, the authors of the present study write. These could include poor knowledge of eye health, concerns about the cost of spectacles, mistrust of optometrists, and limited geographical access in socioeconomically deprived areas.

These impediments could explain why poor people get a glaucoma diagnosis at a more advanced stage of the disease, the authors say.

Following this line of argument, some policy analysts have called for noncommerical ophthalmic or optometric community services to socioeconomically deprived areas, and relocation of eye care services to primary care locations. The funding would come from sources other than fees for service.

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But the authors of the present study argue that poor access to health care would not explain the pattern they observed. ‘On the contrary, if people from more deprived background have greater barriers to health seeking behavior and care, one would expect that they would be less likely to be aware of their diagnosis and not report it,’ the write, ‘and probably less likely to attend health research activities such as UK Biobank.’

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For this reason, if a more accurate study could be done, it would probably show that people of lower economic status were even more likely to suffer from glaucoma than those in this study, the authors speculate.

The authors now plan to carry their research further by exploring structural biomarkers for glaucoma in the UK Biobank, look for an association between end organ damage and socioeconomic status, and use newly available data to explore the biological mechanisms underlying their finding in this study.