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City, University of London’s Professor David Crabb talks to OT  about using big data to map socioeconomic disparities in how late patients present with glaucoma

24 Aug 2018 by Selina Powell

A project that has shone a spotlight on socioeconomic disparities in glaucoma presentation started off with a hunch. Trawling through visual field records as part of an audit of glaucoma management in secondary care, Professor David Crabb began wondering what other uses the large quantities of electronically recorded information could be put to. “It struck me at the time that we have these huge repositories of data that are sitting in the hospital and they might tell us a story,” he shared.

Professor Crabb’s research lab retrospectively gathered information on more than 50,000 patients attending NHS glaucoma clinics in four regions in England.

Anonymised patient data was analysed according to a range of factors, including age, a measure of visual field loss (mean deviation) in the worst eye at first visit to the glaucoma clinic and partial postcode data.

Mapping late presentations

After correcting for age, researchers found that patients in areas with lower socioeconomic status according to the index of multiple deprivation generally had more extensive visual field loss at first presentation than those from higher socioeconomic areas.

“There was a relationship between where a patient lived and how advanced their disease was the first time they presented in the hospital eye service,” Professor Crabb highlighted.

Maps displaying visual field loss revealed ‘hot spots’ for late presentation with glaucoma.

Professor Crabb emphasised that the association between partial postcode data and visual field loss is one factor among many that influences people receiving a late glaucoma diagnosis.

Interactive mapping tools were used by the research team to illustrate and illuminate their results.

"It struck me at the time that we have these huge repositories of data that are sitting in the hospital and they might tell us a story"

Towards a solution

Professor Crabb is quick to point out that the connection between late presentation of eye disease and their socioeconomic status in terms of where they live is well-established. However, he shared his view that, to date, there has been an absence of a deliberate strategy to tackle the issue.

“What we are trying to do with the data is put a spotlight on this that might make people think more about how we incentivise people in certain areas to go to the optometrist,” Professor Crabb said.

“We know from a research perspective that for eye diseases, such as age-related macular degeneration and glaucoma, one of the big factors that influences whether someone is going to be visually impaired is often to do with the way in which people access treatment,” he added.

There are various reasons why people do not visit an optometrist regularly, he shared.

“It might be purely because people are fearful of an eye examination or their vision has been fine throughout their lifetime,” Professor Crabb observed. Some people would be hesitant about going to the optometrist because of the cost of spectacles.

“There are other things like social isolation and language barriers. A lot of older people assume that your vision deteriorates with age, so there is an acceptance of deteriorating vision,” he shared.

Work to make existing technology more accessible could help to ensure that people are diagnosed with eye conditions at the earliest opportunity. Professor Crabb emphasised that lack of technology is seldom the reason for a late diagnosis. “We have the technology – it’s all out there. We just don’t think carefully enough about those people who do not use it,” he said.

“It is often the most marginalised people who are going to be the ones who don’t access those resources,” he added. 

Professor Crabb’s research team have conducted work aimed at making measurements of visual function in glaucoma more convenient for the patient.

He highlighted that most glaucoma patients who are being monitored will only have a perimetry or visual field test twice a year.

“There are 5000 waking hours throughout the year where the patient is not being monitored. We are trying to work out whether it possible to at least monitor patients with glaucoma at home or with a test that is easier to do,” Professor Crabb explained.

The research group is developing a low-cost test that requires a patient to look at a small dot on a monitor or tablet while their eye movements are tracked. Clinical trials using the device are underway in Tanzania and the UK. 

The test relies on research exploring how eye movements are disrupted by glaucoma.

Professor Crabb highlighted that the standard equipment used to measure visual function in glaucoma costs around £30,000.

“It’s an expensive instrument and it’s also an instrument that some people find hard to use. What we are trying to do is develop a low-cost version of the instrument that might be by default something that is more accessible,” he elaborated.

Professor Crabb

A single factor

Professor Crabb emphasised that where a patient lives is only one factor among a large number that influence a patient’s presentation with disease.

He highlighted the asymptomatic nature of glaucoma as a key determinant. “The main reason why people present with the condition in its moderate or severe form is that they just don’t know that they have it. When symptoms do appear, that is typically in the advanced stages of the disease,” Professor Crabb said.

One of the patterns that Professor Crabb noticed during the research related to the placement of optometry practices. The mapping work revealed that optometrists were less evenly dispersed than GP practices.

“There are different drivers associated with where an optometrist will be placed within communities. When you look at the maps, you wonder, ‘Why are there six optometrists here but over here there are none?’”

For example, there is a high concentration of optometry practices in East London close to the City of London, but the practices peter out towards Tower Hamlets.

“Some of that part of London includes the most deprived areas. It seems quite striking,” he highlighted.

A key shift that Professor Crabb would like to see is enhanced links between primary and secondary care.

He noted that good work is being done in this area, with ophthalmology and optometry “much more connected” now than they were a decade ago.

“I think things are turning in the right direction. We need to stress the fact that when you go to your optometrist it is not about correcting your vision with glasses, it is about looking at the back of the eye and working out if someone is at risk of developing an eye condition.”

Image credit: Matthew Horwood

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