Long-Term Follow-Up of Diabetic Retinopathy in Patients with Retinitis Pigmentosa: A Case Series of Nine Patients

Background The coexistence of retinitis pigmentosa and diabetic retinopathy is rare, and the long-term interaction between these two diseases remains poorly understood. Previous studies have suggested that outer retinal degeneration in RP may reduce oxygen consumption and thereby slow DR progression, but longitudinal clinical data are lacking. We present a case series of nine patients with coexisting RP and DM followed for up to 16 years to characterize their long-term clinical course. Case presentation Nine patients with type 2 diabetes and RP were prospectively followed at Beijing Tongren Hospital from 2010 to 2026, including two men and seven women. Age ranged from 27 to 82 years, with follow-up extending up to 16 years. Best-corrected visual acuity at final follow-up was no light perception to counting fingers in nine eyes, 10/100 or worse in two eyes, 20/100 in one eye, and 30/100 or better in six eyes. Three patients developed proliferative diabetic retinopathy; among them, two received vitrectomy and one received panretinal photocoagulation. Diabetic retinopathy was controlled postoperatively, and visual acuity remained stable or slightly improved initially, but gradually declined over long-term follow-up. Five patients showed no diabetic retinopathy changes throughout follow-up. One patient presented with unilateral retinitis pigmentosa and newly diagnosed diabetes mellitus of 2 months' duration; genetic testing revealed heterozygous variants in three retinitis pigmentosa-associated genes. Conclusions In patients with coexisting retinitis pigmentosa and diabetes mellitus, visual function may be more severely compromised than in retinitis pigmentosa alone, even in the absence of diabetic retinopathy changes. The effect of retinitis pigmentosa on diabetic retinopathy progression may depend on the stage of retinitis pigmentosa at diabetes mellitus onset: when diabetes mellitus occurs early, diabetic retinopathy may develop with limited severity; when diabetes mellitus occurs in advanced retinitis pigmentosa, diabetic retinopathy may be absent. Surgical intervention can control diabetic retinopathy but does not prevent the progressive neurodegenerative visual decline associated with retinitis pigmentosa. This case series highlights the complex interaction between these two diseases and the importance of long-term monitoring.