Surabgene Lomparvovec Administered in the Suprachoroidal Space in Adult Participants With Diabetic Retinopathy Without Center-Involved Diabetic Macular Edema

Inclusion Criteria: Ocular (Study Eye for Phase 2b and Phase 3 Portions; Both Eyes for Bilateral Portion) * Moderately severe or severe nonproliferative diabetic retinopathy (NPDR) (early treatment diabetic retinopathy study-diabetic retinopathy severity scale \[DRSS\] level 47 or 53) for which panretinal photocoagulation (PRP) or anti- vascular endothelial growth factor (VEGF) can be safely deferred for at least 6 months after Screening Visit 1. * Best-corrected visual acuity (BCVA) in the study eye of \>= 69 Early treatment diabetic retinopathy study letters (approximate Snellen equivalent 20/40 or better) at Screening Visit 1. Systemic • Diabetic retinopathy (DR) secondary to diabetes mellitus Type 1 or 2 with a hemoglobin A1c (HbA1c)\< 12% within 60 days prior to Screening Visit 1. Exclusion Criteria: Ocular (Study Eye for Phase 2b and Phase 3 Portions; Both Eyes for Bilateral Portion) * Presence of active center involved-diabetic macular edema (CI-DME) in the study eye as determined by spectral domain optical coherence tomography (SD-OCT) evaluated by the central reading center (CRC), using the following threshold: Central retinal thickness (CRT) \>= 320 μm as measured by Heidelberg Spectralis SD-OCT (conversion to equivalent measurement is required and performed by the CRC if imaging is done with another SD-OCT instrument). * Active ocular inflammation including scleral inflammation (including episcleritis) or ocular/ periocular infection present in either eye at Screening Visit 1 or Screening Visit 2 * Neovascularization from a cause other than DR, per investigator * Evidence or documented history of panretinal photocoagulation (PRP) or retinal laser therapy * History of intravitreal therapy, including anti-VEGF and long- or short-acting steroid therapy, within the prior 6 months and documentation of more than 10 prior anti-VEGF or short acting steroid intravitreal injections within 36 months of Screening Visit 1 * Pregnant and breastfeeding individuals are excluded from this clinical study. Systemic * Initiation of intensive insulin treatment (pump or multiple daily injections) within the past 6 months or plans to do so within 52 weeks after Day 1 * Initiation of any treatment containing a GLP-1 receptor agonist within the 3 months prior to Screening Visit 1 or plans to do so within 52 weeks after Day 1 * Pregnant and breastfeeding individuals are excluded from this clinical study