DIABETIC RETINOPATHY

Individualised screening as opposed to routine annual screening of diabetic patients for sightthreatening diabetic retinopathy delivers medical attention more efficiently to where it is needed, thereby achieving optimum results at minimum cost, said Einar Stefansson MD, PhD, University of Iceland, Reykjavik, Iceland.

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Speaking at the 13th EURETINA Congress in Hamburg, Dr Stefansson noted that the prevalence of diabetes is rising throughout the world. In fact, if present trends continue there will be half a billion diabetic patients worldwide by the year 2030. The prevention of vision loss and blindness from diabetic retinopathy will therefore require highly efficient screening in order to contain costs without reducing the detection rate of cases at risk of sight-threatening disease.

“We all know that screening this is very effective and in the countries that have done this, the UK and Nordic countries, the prevalence of blindness among diabetics goes from somewhere like three per cent to five per cent to something like half a per cent,” he added.

Annual screening not best for all

The earliest systematic diabetic retinopathy screening programme began in Iceland in the early 1980s, Dr Stefansson said. The choice of one year as the interval for screening was actually very arbitrary, but it proved to be effective in reducing blindness and has since been endorsed by WHO, the American Academy of Ophthalmology and all the European ophthalmological societies.

However, the Iceland investigators who initiated the screening programmes saw that in any given year only a small percentage of patients needed to be referred for further consultation and treatment. Moreover, they were able to demonstrate that patients with no retinopathy were extremely unlikely to progress to sight-threatening retinopathy where they needed treatment within a period shorter than two years.

They accordingly adopted a new protocol of screening diabetic patients without retinopathy only every two years. After 10 years they published a study that appeared to prove the safety of the approach (Ólafsdóttir, Br J Ophthalmol 2007;91:12 1599-1601). Dr Stefansson and his associates have since taken things one step further and have devised software that enables the calculation of each individual patient’s diabetic retinopathy risk profile as a guide for their screening interval.

“When we do annual screening as is the norm we take the whole group of diabetics, they may have high risk or they may have low risk, but we screen them all at the same interval once yearly. That means that those who are at high risk may not be getting enough screening, but those who are at low risk are screened again and again even though they are always fine,” he said.

Risk factor algorithm

The software’s calculations are based on risk factors for diabetic retinopathy that have been identified in numerous large epidemiological studies. They include such factors as duration of diabetes, type of diabetes, glycaemic control, hypertension, retinopathy status and to a smaller degree, gender.

“We found out that if we combine these six risk factors in an algorithm we can account for 80 per cent of the risk of progression. The remaining 20 per cent can be accounted for by genetics and other factors which have lesser weight in the risk. We developed an algorithm using these known risk factors to calculate each individual’s risk for disease progression and we use that risk profile to determine the appropriate screening interval for each individual patient.

A validation study carried out in Denmark and involving 5,200 diabetics showed that using the algorithm to manage the screening of diabetic patients for retinopathy reduced the average screening interval from 12 months to 29 months (Aspelund et al, Diabetologia 2011 54:2525–2532). “This is a 58 per cent reduction in the frequency of screening, cutting the cost in half, but maintaining the same level of safety. Simply because we are bringing those who are at high risk back sooner but those who are at low risk don't need to come back every year. They can come back every other year or every third year and so forth,” Dr Stefansson said.

Further validation studies, as yet unpublished, have now been concluded in the Netherlands and in England and their results showed even greater reduction in the average interval, also without evidence of safety having been compromised.

Dr Stefansson said that he and his associates plan to make the algorithm available to patients, practitioners and health authorities. One version will mainly be used in conjunction with the databases at screening centres, and the other is a mobile app which patients can use themselves to check their own risk status and advise them as to how they might reduce their risk. “It is clear, and I think it is now proven after the validation studies in Denmark, The Netherlands and England in that individualised diabetic screening of retinopathy risk assessment makes diabetic screening even better,” Dr Stefansson said. Further details are available at: www.risk.is.

Einar Stefansson: einarste@landspitali.is