Differential distribution of manifest lesions in diabetic retinopathy by fundus fluorescein angiography and fundus photography

The present study was a hospital-based, retrospective study. All 55-degree FFA (Spectralis HRA, Heidelberg Engineering, Germany) and 45-degree color FP (TRC-NW8, TOPCON, Japan) images from patients with type 1 or type 2 diabetes mellitus who were diagnosed with DR by comprehensive ophthalmic examination from January 2014 to December 2016, were included in this study. Exclusion criteria included poor image quality due to refractive opacity or misalignment, any fundus disease except for DR, and history of ophthalmological intervention procedure (e.g., laser photocoagulation, vitrectomy, anti-VEGF injection in one or both eyes). This study complied with the Declaration of Helsinki for research involving human subjects and was approved by the research ethics committee of Guangdong Provincial People’s Hospital.

Although ETDRS severity scale is recognized as the “gold standard” for grading the severity of DR in clinical trials, its use in everyday clinical practice has not proven to be easy or practical [17]. In recent more than 10 years, the International Clinical Diabetic Retinopathy Disease Severity Scale provides an important basis for standardizing DR and it is widely used in worldwide. Therefore, based on the Diabetic Retinopathy Disease Severity Scale in this study, DR was classified as follows: no diabetic retinopathy (NDR, no abnormalities), mild NPDR (only subjects with MA), moderate NPDR (subjects with more than just MA but less than severe NPDR), severe NPDR (subjects with any of the following: more than 20 intraretinal hemorrhages in each of 4 quadrants; definite venous beading [VB] in 2+ quadrants; prominent IRMA in 1+ quadrant; and no signs of PDR), and PDR (subjects with one or more of the following: NVE, neovascularization of the disc (NVD), vitreous/preretinal hemorrhage) [17]. In order to show the retinal lesions from the posterior pole to the peripheral retina as clearly as possible, the mydriatic images of FFA and FP were divided into nine fields and were centered on the following areas: the macula (posterior pole), superior mid-peripheral retina, superior temporal mid-peripheral retina, temporal mid-peripheral retina, inferior temporal mid-peripheral retina, inferior mid-peripheral retina, inferior nasal mid-peripheral retina, nasal mid-peripheral retina, and superior nasal mid-peripheral retina (Fig. 1) [18, 19]. The posterior pole was defined as 1 disc diameter (DD) away from the superior, nasal, inferior side to the disc and 1 to 4 DD away from the temporal side of the disc, which consisted of the optic disc, macula, and temporal vessel arches. The mid-peripheral retina was defined as 1 to 4 DD away from the nasal side of the disc and 4 to 6 DD away from the temporal side of the disc. The disease severity level and distribution of typical clinical signs of DR, including MA, intraretinal hemorrhages, exudates (hard exudates and cotton-wool spots), VB, IRMA, NPA, NVE, and NVD, were graded and evaluated based on FFA and FP images by two ophthalmologists (J. W. and X. L.). In cases of disagreement, consensus was reached by discussion with a third ophthalmologist (Q.M.). It is worth noting that the angle of some images might be shown a small deviation due to patient’s poor cooperation during FFA. However, the whole mid-peripheral retina could be clearly displayed because of the overlap of images in each field, according to which the clinical signs of DR could still be accurately identified.

A total of 566 eyes of 324 patients with DR were enrolled in the study, and their demographic and clinical characteristics are shown in Table 1. The mean age was 57.2 ± 10.9 years (24–84 years), and 57.4% of patients were male (186 persons, 316 eyes). Sixty-five eyes had mild NPDR (11.5%), 99 eyes had moderate NPDR (17.5%), 194 eyes had severe NPDR (34.3%), and 208 eyes had PDR (36.8%).

As the earliest clinically recognizable lesion in DR, the distribution of MA in the nine fields exhibited a statistically significant difference (F = 6.39, P < 0.001). The highest frequency of MA were observed in the posterior pole (67.7%), followed by the inferior nasal (59.4%) and the nasal fields (55.4%), without statistically significant differences among the three fields (Table 2).

Because intraretinal hemorrhages and exudates are the other important fundus lesions for moderate NPDR, they were recorded as one clinical sign in this DR stage. There were statistically significant differences for the frequencies of MA (F = 14.5, P < 0.01) and He/Ex (F = 19.54, P < 0.001) in the nine fields. MA were more prevalent in the posterior pole (98.0%), nasal (97.0%), superior (96.0%), inferior nasal (94.9%), and inferior (92.9%) retina, whereas He/Ex were most frequently found in the posterior pole (69.7%) but were significantly lower in other fields (Table 3).

In severe NPDR, besides intraretinal hemorrhages, IRMA, VB, and NPA were the other important clinical signs that were clearly shown in FFA images. Intraretinal hemorrhages were usually widespread throughout the retina, while VB was rarely observed in Chinese patients (frequency of VB was 5.9% [31/526 eyes] in Chen’s report [19] and 6.2% [12/194 eyes] in our study) and thus it was not analyzed in this study. Therefore, the distributions of IRMA and NPA were analyzed as typical lesions in this DR stage. As shown in Table 4, the frequencies of IRMA (F = 34.68, P < 0.001) and NPA (F = 18.77, P < 0.001) were significantly different among the nine fields. The highest frequency of IRMA (60.3%) was found in the inferior nasal mid-peripheral retina with a statistically significant difference compared with the posterior pole, followed by the nasal (53.6%), superior nasal (52.1%), inferior (49.0%), posterior pole (49.0%), and superior retina (41.8%). NPA were most frequently found in 38.7% of the inferior nasal retina, 29.9% of the superior nasal, and 29.4% of the nasal retina, which were significantly higher compared with that in the posterior pole (17.0%).

In view of NVE and NVD as the representative clinical manifestations of PDR, NV of the optic disc or in the retina was analyzed. There was a statistically significant difference in the frequency of NV among the nine fields (F = 42.81, P < 0.001). The frequency of NV in the inferior nasal field was the highest (76.0%), with a statistically significant difference compared to the posterior pole (including NVD, 63.5%). In the superior, inferior, nasal, and superior nasal retina, it was similar to that in the posterior pole (Table 5).

A combined examination of two or more fields usually improves the rate of DR detection. Based on the preceding results, we found that these clinical signs of DR were more prevalent in the posterior pole, nasal, and inferior nasal retina (Table 6, Fig. 2). Therefore, we further compared their frequencies in the posterior pole, posterior pole combined with the nasal field, posterior pole combined with the inferior nasal field, and posterior pole combined with the nasal and inferior nasal field, respectively. As shown in Fig. 3, the frequency of MA in mild NPDR in the three fields (posterior pole + nasal + inferior nasal) was 84.6%, significantly higher than that in the posterior pole (67.7%; P = 0.002), but similar to those in the two fields (posterior pole + nasal: 76.9%, posterior pole + inferior nasal: 78.5%), respectively. In moderate NPDR, there was no statistically significant difference in frequencies of MA (F = 0.31, P = 0.816) and He/Ex (F = 0.50, P = 0.680) among the posterior pole, combined two fields, and three fields. In severe NPDR and PDR, a similar distribution trend was observed for IRMA, NPA, and NV, that their frequencies in the combined three fields were significantly higher than those in the posterior pole and the combined two fields (posterior pole + nasal, or posterior pole + inferior nasal), respectively.