Too Little Evidence to Extend Screening Interval for Diabetic Retinopathy

By Lorraine L. Janeczko

February 09, 2015

NEW YORK (Reuters Health) - Patients with diabetes should continue to be screened for diabetic retinopathy at least once a year, according to a new systematic review by UK researchers.

"There is insufficient evidence to recommend a move to extend the screening interval beyond one year," Dr. Sian Taylor-Phillips of the Warwick Medical School at the University of Warwick in Coventry and colleagues write in the British Journal of Ophthalmology, online January 13.

The team searched for clinical and cost-effectiveness studies in nine major medical databases, including all qualified studies, regardless of study date, or patient age or sex.

There were no randomized controlled trials among the 26 studies they ended up including in their analysis. Observational and economic modelling studies in low-risk patients showed little difference in clinical outcomes between one-year and two-year screening intervals, and the cost-effectiveness studies showed mixed results.

The authors caution, however, that the reliability and validity of these results are limited due to variations in screening and grading protocols and their definitions of low-risk patients.

Also, between 13% and 31% of the patients in the studies were lost to follow up, they note.

"Many of the studies we looked at followed low-risk patients through several years of screening and found that diabetic retinopathy was slow to develop in these groups, but we don't know what happened to those patients who dropped out of the studies. They may have developed retinopathy more quickly," Dr. Taylor-Phillips told Reuters Health by email.

"Also, the studies all used different ways of defining low risk, including lower HbA1c, shorter duration of diabetes, lower systolic blood pressure, not requiring the use of insulin or hypertension treatment, and previous screening results," she added.

"One of the best predictors of rate of progression was whether the patient had any background retinopathy at their previous screen, but to use this in practice to define low-risk patients for longer screening intervals would require consistent methods of screening and grading across different centers," she advised.

Dr. Michael D. Abramoff, who was not involved in the work, said annual screening for diabetic retinopathy through a dilated eye exam is effective but expensive, and that many people with diabetes don't get the screening they need because they don't comply.

"One approach, the subject of this systematic review, is to be smarter about how often patients get screened, and to screen some of them every two or three years instead of every year," said Dr. Abramoff, of the Department of Ophthalmology and Visual Sciences at the University of Iowa Carver College of Medicine in Iowa City.

"Potentially this saves cost, but also, patients who do need treatment may get missed because they are not screened," he told Reuters Health by email. "The fear the authors and I share is that telling our patients to come back for screening in two years instead of one year will lead some of them to lose motivation and drop out entirely -- when we already have so many problems trying to get everyone screened."

Dr. Abramoff added that the patients who dropped out of their studies were those at highest risk, so the studies may have underestimated the risk to patients.

He felt it might be safe to extend the screening interval in some cases, though. "The patients most suited to have an increased interval are the ones who have the best metabolic control and are most likely to follow instructions," he recommended.

Dr. Abramoff suggested that automation may increase efficiency and help lower the cost of screening. He stated that he has patents and patent applications for the automated detection of diabetic retinopathy from retinal images and is a shareholder in a company, IDx, that is trying to commercialize these patents.


Br J Ophthalmol 2015.


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