Transient Mechanical Compression Drives Ultra-Early OCT Changes After Intravitreal Injection

Purpose: To characterize ultra-early optical coherence tomography (OCT) changes following intravitreal injection and to determine whether these changes reflect transient mechanical compression rather than early pharmacologic therapeutic effects. Methods: In this prospective observational study, 40 eyes of 40 patients with macular edema secondary to neovascular age-related macular degeneration, diabetic macular edema, or chronic central serous retinopathy underwent intravitreal injection with bevacizumab (1.25 mg/0.05 mL) or triamcinolone acetonide (4 mg/0.1 mL). Spectral-domain OCT and intraocular pressure (IOP) measurements were obtained at baseline, immediately after injection (15 ± 5 minutes), and at 24 and 48 hours. Central subfield thickness (CST) was recorded at each time point. Associations between CST change, baseline macular thickness, and IOP dynamics were analyzed. Results: A marked reduction in CST was observed at the ultra-early post-injection time point, with a mean decrease of approximately 25% compared with baseline (p < 0.001). This thinning was transient, with substantial rebound by 24 hours and near-complete return to baseline by 48 hours (p = 0.40). Intraocular pressure was uniformly elevated immediately after injection and declined toward baseline by the time of early OCT acquisition. The magnitude of ultra-early CST reduction correlated with baseline CST, with greater thinning observed in eyes with more severe baseline edema. No sustained anatomic differences were observed between treatment groups at 48 hours. Conclusions: Ultra-early OCT improvement following intravitreal injection is dominated by transient mechanical compression rather than pharmacologic drug effect. Retinal thickness measurements obtained within the first 48 hours after injection should therefore be interpreted with caution, as early thinning does not reflect durable therapeutic response.