The formation of NVI is a risk factor for the occurrence of NVG [3–5]. With the progression of DR, retinal ischemia is gradually aggravated, which leads to NVI and even NVG [6, 7]. Early detection of NVI can predict the occurrence of NVG. There is a significant correlation between DI and severity of DR. The severity of DI can be evaluated by IA examination, especially when a clear fundus image can not be obtained due to dioptric media opacities. The IA imaging can provide a crucial basis for determining of the stage of DR , identify high-risk DR patients and offer personalized treatment for the patients with DR. Since the iris vessels in the early stage of DR patients are mostly in the deep layer of iris stoma, and with more iris pigments in Chinese population, it is difficult to detect the lesion at the early stage with slit lamp microscope. Whereas IA can detect early abnormal neovascularization , providing a method of evaluating whether DR patients have NVI.
Numerous researches [10, 11] have found that IFA is easier to find early NVI than IICGA. Through the different characteristics of fluorescein leakage in IFA, we can distinguish iris capillary leakage from NVI. Iris capillary leakage on IFA presented as mild fluorescein leakage with short duration, while NVI presented as moderate or severe leakage with longer duration. Animal experiments found that there was no leakage of iris vessels in IICGA, which could better display the details of iris vessels. IICGA has better diagnostic and application value in iris angiography than IFA . The results of this investigation also suggested that IFA showed NVI filled and leaked rapidly, but in the middle and late stages, with the increase of leakage, IFA could not present the morphology of NVI well. Also, it was difficult to distinguish NVI from pathological iris capillary leakage. On the contrary, IICGA was showing limited NVI leakage, the morphology of abnormal NVI progression was better be observed in middle and late stage, which could well distinguish NVI from iris capillaries. Therefore, we think that IFA combined with IICGA can effectively diagnose NVI and help to distinguish it from iris capillaries or pathological iris capillary leakage.
In order to evaluate the severity of DI in an even better fashion, this research creatively used the self-developed measurement software to accurately measure the circumference range of pupil margin fluorescein leakage. The findings documented that the onset time of iris vascular leakage in PDR patients was significantly earlier than that in severe NPDR patients, and the range of iris vascular leakage in PDR patients was also significantly larger than that in severe NPDR patients, indicating that the more serious the condition of DR, the more obvious the leakage of iris. Among them, NVI was found in 8 patients with PDR who received IA imaging, while in none of patients with severe NPDR. The results demonstrated that with the development of DR, the severity of the retinal ischemia and hypoxia gradually increased and a large amount of neovascular growth factor was released, especially VEGF. The VEGF released into the vitreous cavity gradually spread to the anterior chamber, which eventually led to the formation of NVI. Thereby, the creative quantitative measurement method of IA provides a reference for the application of quantitative evaluation of DI in ischemic ophthalmopathy.
Investigations have found that VEGF is a key factor in the occurrence and development of NVG. Anti-VEGF drugs are an important auxiliary means for the prevention and treatment of NVG, and vitreous injection of anti-VEGF drugs in the short term is a significant strategy for the treatment of NVG [13–16]. In this study, there were 8 PDR patients with NVI. We timely explained the risk of NVG and treatment recommendations to the patients. For the patients with clear dioptric medium, we first injected anti-VEGF drugs into the vitreous cavity, and then completed panretinal photocoagulation (PRP) 2 weeks later. The spot effect was grade 3, and the spot interval was half a spot diameter. For the patients with vitreous hemorrhage, we completed the vitrectomy as soon as possible. PRP was performed during the operation and the spot should be dense enough. Anti-VEGF drugs were given at the end of the operation. Through the above treatment, the NVI of all patients disappeared, the condition was effectively controlled, and did not progress to NVG.
At the same time, this study also found that iris leakage in PDR patients with NVI was significantly more severe than that without NVI. Because the number of PDR patients with NVI was relatively small, we did not statistically analyze the data of the two subgroups and could not draw a more reliable conclusion. In the follow-up study, we will continue to accumulate cases and compare the iris leakage between PDR patients with NVI and without NVI, hoping to obtain reliable indicators for early warning of the occurrence of NVG.
To sum up, quantitative measurement of IA can better evaluate the severity of ischemia in patients with DR and early identify high-risk DR patients prone to NVG, so as to provide a reference basis for personalized treatment of DR.