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Changes in retinal and choroidal thickness and blood flow after anti-VEGF therapy for diabetic macular edema: a retrospective study

This retrospective study demonstrates that three monthly intravitreal conbercept injections significantly improve visual acuity, reduce retinal and choroidal thickness, and enhance superficial and deep capillary plexus perfusion in patients with diabetic macular edema.

Original authors: Yongqi Mao, Fuwen Zhang, Xuan Han, Chuning Wang, Yunhua Tang, Hejiang Ye

Published 2026-07-15

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CC BY 4.0

Original authors: Yongqi Mao, Fuwen Zhang, Xuan Han, Chuning Wang, Yunhua Tang, Hejiang Ye

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your eye's retina as a bustling city map, and the blood vessels are the busy highways delivering oxygen and nutrients to keep the city running. In people with diabetic macular edema (DME), this city gets flooded. High sugar levels in the blood act like a broken dam, causing fluid to leak out of the highways and soak the streets. This swelling (edema) makes the city map thicker than it should be, blurring the view for anyone looking out from the center.

To fix this flood, doctors used a "traffic controller" called conbercept. This is a special medicine injected directly into the eye that acts like a master switch, turning off the signal that tells the blood vessels to leak. The researchers at Chengdu University of TCM wanted to see exactly what happens to the city's map and its traffic flow after flipping this switch. They looked at 45 patients (45 eyes) over a period of 3 months, taking "snapshots" of the eye at the start, 1 month later, and 3 months later.

The Great Drainage
The most obvious change was the water level. Before the treatment, the center of the city (the macula) was puffy, with an average thickness of 392.02 ± 139.90 µm. After the first month of injections, the swelling went down to 338.91 ± 140.32 µm, and by the third month, it settled at 322.26 ± 85.60 µm. The researchers found this drop to be statistically significant, meaning the medicine effectively drained the excess fluid.

But the city didn't just get thinner; the ground underneath it changed too. The layer beneath the retina, called the choroid, also shrank slightly, going from 260.51 ± 106.16 µm down to 243.80 ± 91.15 µm after three months. This suggests the whole "ground" of the eye was less swollen.

The Traffic Flow
Here is where it gets interesting. The researchers used a special camera called OCTA (Optical Coherence Tomography Angiography) to watch the traffic on the highways. They found that the traffic density in the very center of the city (the fovea) actually got better. The "Superficial Capillary Plexus" (the top layer of roads) went from 26.88 ± 6.71 to 29.94 ± 7.32, and the "Deep Capillary Plexus" (the lower roads) improved from 30.02 ± 6.46 to 33.54 ± 6.74. These improvements were real and measurable.

However, not every part of the city saw a traffic boom. The researchers looked at the ring of roads surrounding the center (the inner ring) and the empty zone in the very middle (the Foveal Avascular Zone, or FAZ). They found no significant change in these areas. The FAZ area stayed roughly the same at 0.346 ± 0.152 mm², and the traffic density in the surrounding ring didn't shift much either. This tells us that while the medicine cleared the flood and helped the main roads, it didn't instantly rebuild the empty zones or fix the traffic in the surrounding neighborhoods.

The View Gets Clearer
Because the city drained and the main roads cleared up, the people living there could see better. The patients' vision, measured as LogMAR, improved from a blurry 0.65 ± 0.45 at the start to a much sharper 0.33 ± 0.27 by the end. This wasn't just a guess; the math showed a very strong difference (P < 0.001).

The Safety Check
The researchers also checked for accidents. No one lost their eye, and no serious infections happened. A few patients had a temporary bump in eye pressure or a small bruise on the white of the eye, but these fixed themselves quickly.

What the Study Says (and Doesn't Say)
The study concludes that this "traffic controller" medicine is a great tool for draining the flood and improving vision in the short term. However, the authors are careful to note that this was a retrospective study (looking back at past records) with a small group of people and a short follow-up of only 3 months. They explicitly state that while the central vision improved, the empty zones (FAZ) didn't fill in, and the surrounding traffic didn't change much. They suggest that while the flood is gone, the deep, long-term rebuilding of the blood vessels might take much longer than three months, and we need bigger, longer studies to be sure about the future.

In short: The medicine works like a powerful pump to dry out the wet city and clear the main roads, making the view sharper, but it doesn't instantly rebuild the empty lots or fix the outer neighborhoods.

Technical Summary: Changes in Retinal and Choroidal Thickness and Blood Flow After Anti-VEGF Therapy for Diabetic Macular Edema

Problem Statement
Diabetic macular edema (DME) is a primary cause of central vision loss in patients with diabetic retinopathy, driven by blood-retinal barrier disruption, increased vascular permeability, and inflammation. While intravitreal anti-vascular endothelial growth factor (anti-VEGF) agents are established as the first-line treatment for reducing macular edema and improving visual acuity, the long-term effects of this therapy on retinal and choroidal microcirculation remain incompletely characterized. Specifically, there is a need to clarify the concurrent dynamic responses of retinal and choroidal thickness alongside blood perfusion metrics following anti-VEGF intervention.

Methodology
This retrospective clinical study enrolled 45 patients (45 eyes) with DME treated at the Affiliated Eye Hospital of Chengdu University of Traditional Chinese Medicine between January 2023 and January 2026. All participants received three consecutive monthly intravitreal injections of conbercept (0.5 mg/0.05 mL).

The study utilized Optical Coherence Tomography Angiography (OCTA) via a BM-400K BMizar device (TowardPi Medical Technology) to quantitatively assess structural and perfusion changes at three time points: baseline, 1 month, and 3 months post-first injection. Key parameters measured included:

Structural Metrics: Central macular thickness (CMT) and subfoveal choroidal thickness (SFCT).
Perfusion Metrics: Vessel density of the superficial capillary plexus (SCP) and deep capillary plexus (DCP), foveal avascular zone (FAZ) area, and parafoveal vessel density at 300 µm (FD-300).
Functional Metrics: Best-corrected visual acuity (BCVA) converted to LogMAR.

Statistical analysis employed repeated measures analysis of variance (RMANOVA) with Bonferroni post-hoc tests to evaluate changes over time, with a significance threshold of $P < 0.05$ .

Key Results
The study demonstrated significant improvements in both structural and functional parameters following anti-VEGF therapy:

Visual Acuity: BCVA significantly improved from a baseline of $0.65 \pm 0.45$ LogMAR to $0.33 \pm 0.27$ LogMAR at 3 months ( $P < 0.001$ ).
Retinal Thickness: CMT significantly decreased from $392.02 \pm 139.90$ µm at baseline to $322.26 \pm 85.60$ µm at 3 months ( $P < 0.05$ ), indicating the resolution of macular edema.
Choroidal Thickness: SFCT showed a significant reduction from $260.51 \pm 106.16$ µm to $243.80 \pm 91.15$ µm ( $P < 0.05$ ).
Microcirculation: Vessel density in the foveal SCP and DCP significantly improved at both 1 and 3 months compared to baseline ( $P < 0.05$ ).
Non-Significant Findings: No statistically significant changes were observed in the FAZ area, parafoveal vessel density (FD-300), or vessel density in the inner ring quadrants (superior, inferior, nasal, temporal) of the SCP and DCP ( $P > 0.05$ ).
Safety: No severe complications occurred. Transient intraocular pressure elevation and subconjunctival hemorrhage were observed in a minority of patients but resolved spontaneously.

Key Contributions
This study provides a quantitative evaluation of the therapeutic effects of conbercept on DME using wide-field OCTA. Its primary contribution lies in the concurrent analysis of retinal thickness, choroidal thickness, and layer-specific perfusion metrics. The findings confirm that anti-VEGF therapy not only reduces retinal and choroidal thickness but also enhances microcirculation specifically within the foveal capillary plexuses (both superficial and deep). The study also highlights that while foveal perfusion improves, the FAZ area and parafoveal density may not show significant short-term changes, offering nuance to the understanding of vascular remodeling post-treatment.

Significance and Claims
The authors conclude that anti-VEGF therapy effectively reduces retinal thickness, alleviates macular edema, inhibits neovascularization, and improves visual acuity, thereby enhancing the quality of life for DME patients. The study posits that the observed reduction in CMT correlates with the recovery of blood-retinal barrier function and the absorption of interstitial fluid. Furthermore, the improvement in foveal vessel density suggests a restoration of microcirculation in ischemic areas, although the authors note that recovery in pre-existing non-perfusion areas (such as the FAZ) may require longer durations than the 3-month follow-up provided.

The paper acknowledges limitations, including its retrospective design, relatively small sample size, and short follow-up period. Consequently, the authors state that their findings warrant validation through future prospective, large-sample, multicenter studies with longer follow-up durations to fully explore the time window of microcirculatory recovery and its relationship with long-term prognosis.

Technical Summary: Changes in Retinal and Choroidal Thickness and Blood Flow After Anti-VEGF Therapy for Diabetic Macular Edema

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