**Background:** Bariatric surgery is an effective intervention for weight loss and glycemic improvement in type 2 diabetes (T2D). However, concerns exist that rapid postoperative decline in HbA1c may transiently worsen diabetic retinopathy (DR). Previous studies have yielded conflicting results, and large-scale, register-based evidence on DR progression and ocular intervention needs after bariatric surgery is lacking. This study aimed to evaluate short- and long-term DR outcomes in a nationwide cohort of T2D patients undergoing bariatric surgery.
**Methods:** This was a register-based matched cohort study using Danish national health registers. The cohort was identified from the Danish Registry of Diabetic Retinopathy (DiaBase), which includes all patients screened for DR in Denmark since 2013. Cases were T2D patients ≥18 years who underwent bariatric surgery (ICD-10 code KJDF*) from 2013 to 2022, with index date set as surgery date. Controls were T2D patients without bariatric surgery, matched 1:4.8 by sex, year of birth, and DR level at index date. Patients with fewer than two screening episodes were excluded for screening-specific outcomes. Data were linked across registers to obtain demographics, comorbidities (Charlson Comorbidity Index [CCI]), DR severity (ICDR scale 0–4), laboratory values (HbA1c, lipids, renal function), and medication use. The primary outcome was DR worsening (incident DR [level 1–4] or progressive DR [≥2-step progression or progression to proliferative DR]) assessed at 6 months (±3 months) and 36 months (±9 months). Secondary outcomes included DR improvement (≥2-step regression) and need for ocular intervention (panretinal/focal photocoagulation, intravitreal anti-VEGF injection, vitrectomy) within 1 year and after 1 year. Logistic regression (semi-adjusted and fully adjusted for age, sex, and significant baseline differences) was used for DR outcomes; Cox regression for ocular intervention. Multiple imputation was applied for missing HbA1c values (9.4% cases, 13.7% controls).
**Key Results:** Among 238,967 T2D patients screened, 553 underwent bariatric surgery (0.2%) and were matched to 2677 controls. Median age was 49 years (IQR 42–55), 62.9% female. Cases had shorter diabetes duration (5.1 vs. 6.2 years, p<0.001), lower HbA1c (6.5% [48 mmol/mol] vs. 7.0% [53 mmol/mol], p<0.001), higher CCI scores (moderate low 16.3% vs. 12.8%, p=0.002), and more frequent use of metformin (82.1% vs. 70.3%), GLP-1 analogues (49.6% vs. 21.1%), SGLT-2 inhibitors (17.7% vs. 14.4%), and antihypertensives (73.4% vs. 56.6%) (all p<0.05). DR worsening at 6 months occurred in 2.9% of cases vs. 8.4% of controls; at 36 months, 5.2% vs. 7.9%. In fully adjusted models, odds of DR worsening were not significantly different: short-term OR 0.41 (95% CI 0.13–1.33, p=0.14); long-term OR 0.71 (95% CI 0.34–1.46, p=0.35). DR improvement also showed no significant difference (short-term OR 1.25 [95% CI 0.07–21.67]; long-term OR 3.25 [95% CI 0.31–34.00]). Fewer than 5 cases of intravitreal injections occurred post-surgery, precluding statistical analysis. Post-hoc stratification by pre-existing DR showed no increased odds of worsening. Biochemical analysis revealed that cases maintained lower HbA1c than controls at all time points (pre-surgery 6.5% vs. 7.0%; short-term 5.8% vs. 6.9%; long-term 5.9% vs. 7.2%, all p<0.001). Triglycerides decreased in cases post-surgery and remained lower than controls (1.29 vs. 1.81 mmol/L short-term; 1.40 vs. 1.76 mmol/L long-term, p<0.001). Renal function remained within normal limits in both groups.
**Clinical Implications:** This nationwide study provides robust evidence that bariatric surgery in T2D patients with good preoperative glycemic control does not increase the risk of short- or long-term DR worsening or the need for ocular interventions. The findings align with recent meta-analyses suggesting a neutral or protective effect, contrasting with earlier concerns about early worsening. The low progression rates may reflect the benefits of preoperative optimization (glycemic stability, weight loss, lifestyle changes) and the effectiveness of DR screening programs. Clinicians can reassure patients that bariatric surgery appears safe from a retinal perspective, particularly when glycemic control is well managed before surgery. Limitations include the lack of BMI data for controls, reliance on screening attendance, and inability to stratify by surgery type. Further research should explore outcomes in patients with poorer baseline glycemic control and longer follow-up.