16.4.2Phase 3: Implementation of the Screening Model

The results corresponded to the period from January 2008 to December 2010, during which time, 4,729 patients with diabetes were referred for screening. In 3,514 (74%) cases, the images were considered normal, and an e-mail report was sent to the referring GPs with a recommendation for a new appointment in 1 year. In the other 1,215 (26%) cases, the images were sent for assessment by ophthalmologists. The ophthalmologists determined that 690 (15%) patients did not have DR (false positives), 429 (9%) had DR, and 96 (2%) patients had unreadable images (Table 16.1). Based on those data, the speciÞcity of the GPs participating in our study for detecting DR by nonmydriatic retinography was 83%.

Among the 429 patients with some degree of DR, 325 (7%) had mild nonproliferative DR (NPDR), 84 (2%) had moderate NPDR, 15 (0.3%) had severe NPDR, and Þve (0.1%) had PDR (Table 16.2).

Of the 690 patients without DR, 297 (6%) had a normal fundus and 393 (8%) had other retinal alterations. Of them, 189 (4%) had drusen, 94 (2%) had nevi, and 47 (1%) had lesions related to myopia. Less frequent causes of false positives were AMD, epiretinal membranes, and retinal vein occlusions.

To assess the percentage of false negatives, the retinal images of 360 patients (30 from each GP each year) whose fundi were considered normal were chosen randomly to be reread by ophthalmologists. Of them, 19 patients (5%) had some degree of DR; 15 patients were classiÞed with mild NPDR, one patient with moderate NPDR, and three patients (1%) had treatable DR with hard exudates in the macular area. Considering these data, the sensitivity of GPs for detecting DR was 95% and the sensitivity of GPs for detecting treatable lesions was 99%.

When the results of the 3 years were considered globally to evaluate tendencies, a signiÞcant (p < 0.00) decrease in the percentage of unreadable images was detected. We also found a signiÞcant (p = 0.03) decrease over 3 years in the percentage of false negatives. The other data were not signiÞcant.

16.5Discussion

16.5.1Evaluation of the Screening Model

The use of telemedicine based on nonmydriatic retinography is a reliable screening tool for DR. Trained nurses or technicians obtain digital retinal images that ophthalmologists later assessed

to determine which patients require a more exhaustive evaluation. In the current study, we described a different approach in which GPs were the initial readers of the retinographies. The results indicated that trained GPs can perform DR screening with high reliability. The British Diabetic Association recommends a sensitivity of at least 80% and a speciÞcity of at least 95% with respect to the gold standard for that screening technique to be considered adequate [19]. The four GPs in the current study obtained a speciÞcity of 83% and a sensitivity of 95%. The sensitivity for detecting treatable lesions was 99%. The GPs detected most treatable lesions but inappropriately referred 14% of patients. A sensitivity of 95% means that 5% of affected patients are diagnosed as normal. It is important to point out that most false negatives were patients with mild NPDR who had only one or a few posterior pole microaneurysms. Even experienced ophthalmologists can have difÞculty differentiating these cases from those with a normal fundus. Moreover, these false negatives are not clinically relevant because this condition does not require treatment and the fundus will be assessed again in 1 year. In any event, a signiÞcant progressive decrease in the percentage of false negatives was detected over the course of the study. This decrease can be due to the fact that the GPs improved their ability to detect DR.

Most inappropriate referrals in the study were for patients with normal fundi, but a high proportion was due to drusen, nevi, or high myopia. In this group of patients, only a low percentage corresponded to retinal alterations that were treatable, such as epiretinal membranes, retinal vein occlusions, or AMD. There was no decrease in the percentage of inappropriate referrals when the data from the 3 years were compared, indicating that, at least during this period, the GPs did not improve their ability to differentiate DR from the related entities. During the training phase, the four GPs were instructed to differentiate DR from drusen, pigmented retinal lesions, or myopia. However, considering the distribution of the inappropriate referrals obtained in the current study, it seems reasonable that further training in these conditions may reduce the percentage of false

positives and improve the sensitivity of the screening technique.

In 2004, Gill et al. [20] evaluated the accuracy of GPs in screening for DR with a PanOptic ophthalmoscope (Welch Allyn, Skaneateles Falls, NY, USA) and obtained a sensitivity of 87% and a speciÞcity of 57%. They concluded that the technique could not replace routine referral to an ophthalmologist because of the low speciÞcity. In more recent reports, Farley et al. [11], Askew et al. [12], and Romero et al. [14] have suggested an approach similar to the one described in this chapter with the introduction of GPs into the screening process for DR using nonmydriatic retinography. Farley et al. [11] reported a sensitivity of 89.8% for the eight primary care physicians who participated in their study. Askew et al. [12] reported a sensitivity of 87% and a speciÞcity of 95% for the two GPs in that study. In both studies, all retinal images were reread by ophthalmologists, and both studies concluded that GPs can screen DR effectively using nonmydriatic retinography. The difference from the current study was that we did not attempt to evaluate the agreement between GPs and ophthalmologists in the interpretation of the retinographies of patients with diabetes. We reported previously that after adequate training, the agreement was high between ophthalmologists and GPs in evaluating retinographies [13]. We are now evaluating the model of DR screening performed by GPs 3 years after implementation. We found only one recent similar study in the literature by Romero et al. [14], who reported a sensitivity of 95% and a speciÞcity of 98% for the GPs.

16.5.2 Prevalence of DR

The prevalence of DR among the patients of the current study was 9%. Considering that the percentage of false negatives in a sample of 360 patients was 5%, an overall prevalence of DR of about 14% could be considered. The prevalence of DR found in the current study was lower than the prevalence expected among the general population of patients with diabetes. Kempen