A logistic regression analysis model considering age, gender, body mass index, waist circumference, serum creatinine, eGFR, CRP, HbA1c, and fasting blood glucose, along with PNI, showed that PNI was an independent risk factor for diabetic retinopathy in type 2 diabetes mellitus patients, since a unit decrease in PNI increased the odds of diabetic retinopathy by 106% (p = 0.001, OR: 1.068, 95% CI: 1.03–1.10). The gene discussed is CRP; the disease is diabetic retinopathy.