All patients in this study were diagnosed with type 2 diabetes by the department of endocrinology. The average diabetes duration was 12.7 years, and all the lesion eyes met the inclusion criteria to ensure reliable case diagnosis and credible observation results.
PDR mostly manifests as fresh vitreous and retinal hemorrhage, fibroproliferative membrane with active neovascularization and/or TRD clinically.
We found that a small number of PDR patients had relatively "quiet" fundus performance.
In order to distinguish it from traditional PDR, we definited this type of PDR with “quiet” fundus as IPDR. Combined with the preoperative examination and intraoperative observation, we found it has the following characteristics:(1)All occurred after PRP treatment;༈2༉No fresh vitreous and retinal hemorrhage;༈3༉The fibroproliferative membrane was yellowish-white in appearance without active neovascularization, mainly located on the surface of the optic disc and/or around the vascular arcade;༈4༉TRD was limited, and mostly located around the optic disc and/or vascular arcade;༈5༉The optic disc was pale. The mid-peripheral retina was thin, and mostly accompanied by small branch artery and vein occlusion;༈6༉The incidence of PVD was low. The vitreous and retina adhered closely. It was relatively difficult to completely remove the fibroproliferative membrane during the operation, and iatrogenic retinal break was extremely prone to occur.
Non-proliferative diabetic retinopathy (NPDR) often develops slowly. However, PDR develops rapidly due to the formation of neovascularization. The fundus performance of PDR is active. But, the fundus performance of IPDR is relatively quiet. We consider the reasons as follows: (1) HbA1C is proposed as a medium and long-term measure of average glycemia, and it is a serious risk factor for DR. Strict control of glycemia can delay the development of DR[10, 11].
Patients in this study had a relatively long history of diabetes and had rich experience in controlling glycemia.
The result of HbA1C measurement showed that the patient's long-term glycemic control is relatively ideal. Therefore, the progress of IPDR was relatively slow; (2) Panretinal laser photocoagulation is an effective method for treating DR. Melanosomes located within the retinal pigment epithelium (RPE) absorb the laser energy that causes a thermal injury and coagulates the adjacent photoreceptors and RPE cells. As photoreceptors are metabolically the most active cells in the retina with high oxygen consumption, photocoagulation lowers the metabolic load and reduces the ischemia and ischemia-driven angiogenic substances[12]. Photocoagulation plays an important role in controlling or delaying the development of DR[13, 14]. In this study, all eyes were treated with PRP for an average of 1.6 years before surgery, which effectively alleviated the hypoxia and ischemia of the retina; (3) The occlusion of small branch arteries can cause ischemia and necrosis of retinal inner cells, and PRP can also make the neurosensory retina thin due to the damaged retinal cells including photoreceptors and ganglion cells [12]; These factors lead to thinning of the retinal tissue and reducing oxygen demand so that the oxygen demand and oxygen supply of the retina reach a relatively balance state. During the operation, we found that the retinal tissues in the middle and periphery of the IPDR eyes were relatively thin, which further confirmed the hypothesis.
The vitreous adhered tightly to the retina in the eyes of IPDR, and the vitrectomy was relatively difficult, which easily induced iatrogenic retinal break. All patients in this study were performed by surgeons with more than 15 years of experience in vitreoretinal surgery, 14 eyes (35%) still occurred iatrogenic retinal break when the retinal fibroproliferative membrane was removed. Considering that the fundus performance of IPDR is relatively quiet, we suggest that vitrectomy for such patients should be performed in accordance with the principle of minimal quantification. During the operation, we just need to remove the opaque vitreous, cut off the proliferation cord and relieve the local traction, it is not necessary to completely remove the fibroproliferative membrane to minimize retinal damage and avoid iatrogenic retinal break; If iatrogenic retinal break occurs inadvertently during the operation, we should remove fully the fibroproliferative membrane, and select the tamponade (silicone oil or C3F8) according to the condition. Considering that all the eyes in this study had been treated with PRP before surgery, and the retina had no obvious ischemia and hypoxia, if there was no iatrogenic retinal break, retinal photocoagulation was not performed, but if it occurred, photocoagulation was performed only on the edge of the break to block it.
The BCVA at the end of follow-up after vitrectomy was improved compared with that before surgery. However, postoperative visual acuity in one patient worsened from the preoperative status, two patients were lost to follow-up and all others improved or were stable. The main reasons for no improvement of visual acuity after the vitrectomy in some patients are the atrophy and thinning of the retina of the lesion eyes and the long-term macular tractional detachment.
Due to the relative unsatisfactory prognosis of IPDR and the difficulty of surgery, surgeons with rich experience in vitreoretinal surgery can consider vitrectomy for patients after fully communicating with patients and obtaining the patients’ consent.
The limitations of this study include its limited sample size and retrospective nature. Also, it lacks controlled observation results of long-term non-surgical treatment in IPDR. However, because of the limited previously published reports in this field, this study provides important observations and insights on the characteristics of IPDR and the efficacy of vitrectomy.