Objective To observe the effectiveness and safety of subretinal dexamethasone injection in treating refractory diabetic macular edema (DME). MethodsA prospective case study. From January 2024 to March 2024, 9 refractory DME patients with 10 eyes diagnosed in Tianjin Eye Hospital were included. All eyes had a central macular thickness (CMT) of more than 275 μm despite undergoing anti-vascular endothelial growth factor therapy at least 5 times. 25G pars plana vitrectomy was performed for the patients combined with internal limiting membrane peeling and subretinal injection of dexamethasone sodium phosphate. Patients underwent ophthalmic evaluation, including best-corrected visual acuity (BCVA), microperimetry and optical coherence tomography testing before surgery and 1 month and 3 months postoperatively. The international standard visual acuity chart was used for BCVA examination, which was statistically converted into logMAR visual acuity. The BCVA, the mean sensitivity (MS) and the CMT before and after surgery were compared using paired t test. The intraoperative and postoperative complications were recorded. ResultsNine cases had 10 eyes, 4 males had 5 eyes and 5 females had 5 eyes. Age 43-79 (65.3±10.8) years old. logMAR BCVA was 0.84±0.25, 0.72±0.31 and 0.63±0.22 before and 1 and 3 months after surgery, respectively. MS was (16.48±5.03), (16.6±6.31), (18.0±5.33) dB, respectively. CMT was (437.5±90.4), (306.9±87.4), (288.7±87.3) μm, respectively. Compared with before surgery, BCVA: 1 month after surgery had no statistically significant difference (t=2.025, P=0.074), 3 months after surgery had statistically significant difference (t=5.161, P=0.001); MS: 1 and 3 months after surgery, there was no significant difference (t=－0.078, －1.022; P=0.940, 0.334); CMT: the difference was statistically significant 1 and 3 months after surgery (t=2.892, 3.175; P=0.018, 0.011), and the difference was statistically significant 1 and 3 months after surgery (t=2.427, P=0.038). There were no complications such as macular hiatus, vitreous hematoma and retinal detachment during and after surgery in all patients. During the follow-up period, there was no increase in intraocular pressure and cataract. ConclusionThe combined treatment strategy involved pars plana vitrectomy, internal limiting membrane peeling and subretinal injection of dexamethasone can effectively reduce CMT in refractory DME patients, improve visual acuity and have good safety.