Mecobalamin Combined With Anti-VEGF Intravitreal Injection for Retinal Vein Occlusion Treatment

Retinal vein occlusion (RVO) is the second leading cause of vision loss resulting from retinal vascular disease, with a prevalence of approximately 0.6%-1.6%. Macular edema (ME) secondary to RVO is a common cause of vision loss. RVO induces hypoxia and ischemia, leading to neuronal loss and increased vascular permeability. Therefore, anti-vascular endothelial growth factor (anti-VEGF) injections are widely used as first-line treatment for RVO-ME, achieving remarkable therapeutic effects. Pivotal trials (BRAVO and CRUISE) demonstrated that anti-VEGF therapy significantly improves best-corrected visual acuity (BCVA) and reduces retinal swelling, enhancing BCVA by 12-15 ETDRS letters and decreasing central subfield thickness (CST) by about 200 μm.

However, therapies targeting VEGF alone may not sufficiently manage this condition. Although anti-VEGF agents improve edema and short-term visual acuity, long-term efficacy is limited by frequent injections and inadequate nerve repair. Additionally, anti-VEGF fails to reverse neurodegenerative changes such as photoreceptor apoptosis and Müller cell activation. Consequently, combined strategies synchronizing vascular leakage repair and neuroprotection have become an international research priority.

As a typical neurotrophic drug, mecobalamin repairs nerve tissue and accelerates axonal regeneration and myelination. Mecobalamin, a vitamin B12 derivative, is more readily absorbed by nerve cells than vitamin B12 itself. As a methyl donor, it facilitates homocysteine-to-methionine conversion, supporting nucleic acid, protein, and phospholipid synthesis critical for myelin formation. This process is essential for nerve myelin formation and repair. Mecobalamin accelerates lipid, protein, and nucleic acid metabolism in neurons, enhancing nerve function recovery and alleviating neurological symptoms. Previous studies found that oral vitamin B1 and mecobalamin improve corneal nerve fiber density. The neuroprotective drug was shown to attenuate oxidative stress in animal models, but clinical translation evidence remains insufficient.

Notably, VEGF exhibits dual roles as both a permeability factor and neuroprotectant. Excessive VEGF inhibition may exacerbate retinal ganglion cell apoptosis. Although mecobalamin promotes neural repair, its spatiotemporal synergy with anti-VEGF in neurovascular unit (NVU) recovery remains uncharacterized. This prospective, double-blind, randomized controlled trial evaluates the synergistic effects of mecobalamin combined with anti-VEGF therapy on NVU repair in RVO-ME, utilizing dual-targeted "vascular intervention + neuroprotection" to overcome current limitations.

Current ME efficacy assessment relies primarily on optical coherence tomography (OCT)-derived CST, with few tertiary centers employing OCT angiography (OCTA), multifocal electroretinography (mfERG), or adaptive optics (AO). Existing metrics inadequately characterize NVU function or anti-VEGF effects on non-vascular components (glia, photoreceptors). The absence of standardized NVU repair quantification impedes cross-study comparisons. To address this, the investigators propose a multimodal "OCT structural tomography + OCTA flow stratification + AO cellular morphology + microperimetry functional mapping + mfERG functional localization" assessment to establish a new therapeutic standard.

Primary objectives:

1. Evaluate mecobalamin combined with anti-VEGF therapy on CST and BCVA improvement in RVO-ME patients 2. Validate mecobalamin's synergistic contribution to NVU repair using multimodal imaging

This prospective, double-blind, randomized controlled intervention study will enroll RVO patients at the First Affiliated Hospital of Chongqing Medical University from 1 August 2025 to 31 July 2027. The study aims to evaluate mecobalamin combined with conbercept on retinal NVU repair in RVO-ME patients. The Institutional Review Board approved the protocol (No. 2025-387-01) on 26 May 2025. The study adheres to the Declaration of Helsinki and Ethical Guidelines for Medical and Biological Research Involving Human Subjects. All participants will provide written informed consent; an opt-out approach will be implemented where applicable.

Primary outcomes will be assessed at 12 months post-initial treatment. Eligible patients will be identified during initial ophthalmology visits. Recruitment will be performed by ophthalmologists. After eligibility confirmation and informed consent, standard treatment commences immediately. Reasons for non-participation will be documented. Enrolled eyes will receive alphanumeric ID codes and be randomly assigned to treatment groups two days before intervention using block randomization (Statistical Package R, v3.6).

Treatment groups (1:1 randomization):

Experimental: Intravitreal conbercept (0.5 mg monthly × 3 months, then pro re nata) + oral mecobalamin (0.5 mg TID × 6 months) Control: Identical anti-VEGF regimen + placebo capsules (TID × 6 months)

Recurrence criteria:

* CST increase ≥50 μm from minimum recorded value * BCVA decrease ≥5 ETDRS letters * New/increased intraretinal/subretinal fluid

Assessments occur at baseline, initial treatment day, and 1, 3, 6, 9, and 12 months post-treatment. Follow-up requirements are detailed in supplementary materials. Study exit occurs at 1-year completion or if:

1. Three consecutive missed visits 2. Poor compliance/withdrawal request 3. New systemic disease affecting outcomes

Protocol violators or cases with essential missing data will be excluded from per-protocol analysis. Clinical trial staff will collect data under investigator supervision. Researchers will ensure data accuracy, completeness, and timeliness. The schedule for enrollment, interventions, and assessments is outlined in supplementary materials. Clinical/ophthalmic data will be entered into an electronic data capture system. All data will remain confidential per regulatory requirements.

• Change in best-corrected visual acuity (BCVA) [Time frame: From enrollment to the end of treatment at 1 year]
• capillary density [Time frame: From enrollment to the end of treatment at 1 year]
• Cone photoreceptor distribution characteristics [Time frame: From enrollment to the end of treatment at 1 year]
• Mean light sensitivity and fixation stability [Time frame: From enrollment to the end of treatment at 1 year]
• Serum vitamin B12 levels [Time frame: From enrollment to the end of treatment at 1 year]
• the number of treatments [Time frame: From enrollment to the end of treatment at 1 year]
• Frequency of injection (times per year), interval time [Time frame: From enrollment to the end of treatment at 1 year]
• incidence and severity of AEs and serious adverse events (SAEs) [Time frame: From enrollment to the end of treatment at 1 year]