False positives explained

Optometrist and AOP clinical director, Peter Hampson, discusses the Association’s newly released false positive referral factsheet

Sight test equipment

Why did the AOP decide to produce this infographic and information about false positive referrals?

It was mainly in response to the fact that one of the most common criticisms that we hear from secondary care is that optometrists over refer, and we don’t think that is fair. It is about trying to explain that what is currently deemed and seen as over referral by secondary care, does not actually reflect what is currently going on in primary care.

Referring to the infographic, what is key for members to understand?

The main thing to highlight on the infographic is that for most low prevalence eye diseases, a 50% false positive rate is good. We have tried to explain this visually on the infographic using the purple and grey dots.

What our disease prevalence example for glaucoma demonstrates is that optometrists are seeing a lot of people, most of who are completely normal. The people they are trying to identify with the disease are represented by the purple dots on the infographic, which is a very small proportion in comparison to those they see. Therefore, for optometrists, it’s like having a large bag of ping pong balls with only a handful of coloured ones. Optometrists are very efficient at finding the coloured balls, but unfortunately sometimes they collect a few white ones in the process.

The message that we would like people to take away from this is that optometrists are doing a good job

 

The example on the infographic shows that for every 10,000 people, 9800 people will not have glaucoma, but 200 will. Of the 10,000 people, 392 will be referred. What this shows is that optometrists are really good at finding the right people who need referring, but unfortunately, we do pick up some people incorrectly too, and there is nothing we can do about that.

However, if you are in secondary care and you observe that 50% of referrals are false positives, it is easy to see this negatively. Yet what they don’t see is that great big number of people who are seen and correctly not referred – it’s about contrasting the two statistics so that those in secondary care see and understand the different between what walks into practice and what walks into secondary care.

The message that we would like people to take away from this is that optometrists are doing a good job.

What we would like members to do is use the infographic to highlight to those working in secondary care that optometrists are doing a good job at identifying those with disease

 

How do you encourage members to use the infographic?

What we would like members to do is use the infographic to highlight to those working in secondary care that optometrists are doing a good job at identifying those with disease.

The only way to get rid of the 50% of false positives who are referred into secondary care for low prevalence diseases such as glaucoma would be to repeat test and have additional tests that were able to refine the process. However, this needs additional funding.

It is important to highlight that although performing additional tests could improve false positives, it doesn’t mean that we are not already doing a good job.

To read more about false positive referrals and to download the information, visit the AOP’s website.  

Image credit: Getty/BiZaMox

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Comments (2)

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  • Peter Hampson, AOP Clinical Director02 December 2019

    Thanks for the feedback, we do show in the infographic that this sensitivity and specificity are far better than the real world. We also point out that even at these levels some people are missed. The aim is to show that even if the test was this good, unfortunately optometrists would refer some 'false positives', but that isn't because they aren't doing a good job.

    Greater feedback on referrals is something that we push for every time we discuss connectivity, or referral schemes. We agree this would be beneficial not only for secondary care, but also for skill development for optometrists.

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  • davidfarmilo28 November 2019

    Working in a new referrals clinic shows a different slant on referrals. What would be useful would be to campaign for greater feedback on the appropriate findings on referral into secondary care and how appropriate the referral was. The AOP example also assumes 100% of glaucoma cases are picked up which is not true. Having a more realistic approach on sensitivity and specificity might lead to a better debate on how to consider setting up referral refinement schemes either in the community or in secondary care.

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