Most people with diabetes know that high blood sugar can damage their eyes over time. But scientists are discovering that the opposite problem blood sugar dropping too low may also contribute to changes in the retina that threaten vision.
A study published in Science Translational Medicine on April 30, 2025, investigated how hypoglycemia (low blood sugar) affects the blood-retinal barrier, the protective structure that helps regulate movement between retinal tissue and the bloodstream.
Researchers from the Wilmer Eye Institute at Johns Hopkins Medicine found that temporary episodes of low blood sugar triggered changes in proteins known as hypoxia-inducible factors (HIFs). In diabetic mice, these changes increased leakage from retinal blood vessels, potentially contributing to the processes involved in diabetic retinopathy.
The researchers also tested an experimental compound called 32-134D, which blocked these damaging changes in diabetic mice.
Although the findings offer new insights into diabetic eye disease, they do not establish that every episode of low blood sugar causes permanent vision damage in people.
Instead, the research highlights the importance of maintaining stable glucose levels while avoiding both prolonged hyperglycemia and dangerous hypoglycemia.
What Is Diabetic Retinopathy?
Diabetic retinopathy is a complication of diabetes that affects the blood vessels and supporting nerve tissue in the retina.
The retina is the light-sensitive tissue at the back of the eye. It converts incoming light into electrical signals that travel through the optic nerve to the brain, allowing us to see.
Over time, diabetes can damage the retina’s delicate blood vessels, causing them to leak fluid, become blocked, or stimulate the formation of abnormal new blood vessels.
These changes may interfere with normal retinal function and eventually lead to permanent vision loss.
According to the National Eye Institute (NEI), diabetic retinopathy can affect people with either type 1 or type 2 diabetes.
Common Symptoms of Diabetic Retinopathy
Early diabetic retinopathy often develops without noticeable symptoms.
As the condition progresses, possible symptoms include:
- Blurred or fluctuating vision.
- Dark spots or floating shapes in the visual field.
- Difficulty seeing clearly at night.
- Areas of missing vision.
- Progressive loss of visual sharpness.
- Severe vision loss in advanced disease.
However, the absence of symptoms does not mean the retina is healthy.
Regular diabetic eye examinations remain essential because specialists can detect changes before patients notice vision problems.
Why Does Diabetic Retinopathy Develop?
Chronic high blood sugar is one of the most established contributors to diabetic retinopathy.
Elevated glucose can damage retinal blood vessels through several interacting biological processes, including oxidative stress, inflammation, and changes in vascular function.
Other important risk factors include longer diabetes duration, high blood pressure, kidney disease, and abnormal blood lipid levels.
The new research does not challenge the established importance of controlling high blood sugar. Instead, it identifies another possible mechanism through which unstable glucose levels may affect retinal health.
Understanding the Blood-Retinal Barrier
To understand why low blood sugar may matter, it helps to examine an important protective structure inside the eye: the blood-retinal barrier (BRB).
The blood-retinal barrier controls the movement of water, ions, nutrients, and other substances between the bloodstream and retinal tissue.
It helps maintain a stable environment needed for the retina’s highly specialized nerve cells to function properly.
The barrier has two main components:
The inner blood-retinal barrier (iBRB) is formed mainly by specialized endothelial cells lining retinal blood vessels. Supporting cells, including pericytes, glial cells, and other components of the retinal neurovascular unit, help maintain its function.
The outer blood-retinal barrier is formed by the retinal pigment epithelium, a specialized cell layer that supports the retina’s light-sensitive photoreceptors.
When the inner barrier becomes damaged, blood vessels may leak fluid and proteins into surrounding retinal tissue.
This leakage can contribute to swelling, inflammation, and disruption of normal visual function.
When fluid accumulates in the macula—the central retinal region responsible for detailed vision—the condition is known as diabetic macular edema.
The 2025 Johns Hopkins research focused on how hypoglycemia could contribute to breakdown of the inner blood-retinal barrier.
The 2025 Study: How Low Blood Sugar May Damage Retinal Blood Vessels
The study, titled Hypoglycemia Promotes Inner Blood-Retinal Barrier Breakdown and Retinal Vascular Leakage in Diabetic Mice, was published on April 30, 2025.
Led by Chuanyu Guo and colleagues, with Akrit Sodhi as corresponding author, the research explored why some patients experience worsening diabetic retinopathy when blood glucose levels change rapidly during treatment.
The researchers investigated whether periods of low blood sugar activate molecular pathways that increase blood vessel permeability in the retina.
Their experiments involved diabetic and non-diabetic mice, retinal tissue analysis, and tests of a compound designed to inhibit HIF activity.
Original peer-reviewed research: Science Translational Medicine, DOI: 10.1126/scitranslmed.adq5355
Finding 1: Low Blood Sugar Increased HIF Proteins
Researchers observed that hypoglycemia caused an accumulation of two transcription factors in retinal cells:
- Hypoxia-inducible factor-1 alpha (HIF-1α).
- Hypoxia-inducible factor-2 alpha (HIF-2α).
HIF proteins help cells regulate gene activity in response to conditions such as reduced oxygen availability.
The experiments showed that hypoglycemia could also activate these pathways in the retina.
HIF activation increased the expression of several molecules associated with blood vessel permeability.
These molecules can make retinal blood vessels more likely to leak.
Finding 2: Diabetic Retinas Were More Vulnerable
One of the study’s most important observations was the difference between diabetic and non-diabetic mice.
Low blood sugar activated HIF-related responses in the retina, but the resulting vascular leakage was particularly significant in diabetic mice.
In the diabetic animals, these molecular changes were sufficient to disrupt the inner blood-retinal barrier.
The researchers identified increased movement of substances through endothelial cells, a process known as vesicular transcytosis.
This helped explain how the retinal barrier could become more permeable.
The results suggest that a retina already affected by diabetes may be more vulnerable to additional stress caused by glucose fluctuations.
However, animal findings cannot automatically be generalized to people with diabetes, and the experiments did not establish how often hypoglycemia causes lasting retinal damage in humans.
Finding 3: An Experimental Drug Prevented Leakage in Diabetic Mice
The researchers evaluated a compound called 32-134D, designed to inhibit both HIF-1 and HIF-2 signaling.
When administered through an injection into the eyes of diabetic mice, the compound prevented the hypoglycemia-associated increase in HIF-regulated vascular permeability factors.
It also blocked the breakdown of the inner blood-retinal barrier observed during the experiments.
Additional laboratory work showed that the compound could inhibit relevant HIF-associated responses in human retinal tissue.
These findings suggest that HIF inhibition could become a promising research direction for diabetic retinopathy.
However, 32-134D remains experimental for this application. The study did not demonstrate that it is safe or effective as a treatment for diabetic retinopathy in human patients.
Clinical testing would be required before its use could be recommended.
Why Would Low Blood Sugar Affect the Retina?
Glucose is an important energy source for the retina, which has substantial metabolic demands.
When blood glucose falls, retinal cells must adapt to changes in available energy.
The Johns Hopkins study identified a pathway connecting these changes to vascular permeability.
The proposed process can be summarized as follows:
- Blood glucose falls during an episode of hypoglycemia.
- Retinal cells accumulate HIF-1α and HIF-2α.
- HIF signaling increases the expression of molecules that affect blood vessels.
- In diabetic mice, these molecules increase endothelial permeability.
- The inner blood-retinal barrier becomes disrupted, allowing greater vascular leakage.
Importantly, this sequence represents an experimentally supported mechanism observed principally in mouse models.
It is not proof that a single mild episode of low blood sugar will cause retinopathy in an individual patient.
What Does Human Research Show?
Although the 2025 study largely examined diabetic mice, earlier clinical research has investigated how low blood sugar affects the retinal circulation in people.
A 2023 study, Retinal Microvascular Density and Perfusion During an Insulin-Induced Hypoglycemia Episode: A Warning Call, evaluated changes in retinal blood vessels during hypoglycemia.
The researchers included 52 participants and analyzed 97 eyes using optical coherence tomography angiography, or OCTA.
OCTA is a non-invasive imaging technique that measures retinal blood flow and vascular characteristics.
The investigators observed significant changes in retinal vascular perfusion and density during hypoglycemia.
These findings provided human evidence that low blood sugar can temporarily alter the retinal circulation.
However, the study did not establish that these short-term changes necessarily produce permanent retinal damage.
Read the research: Retinal Microvascular Density and Perfusion During an Insulin-Induced Hypoglycemia Episode — Full Text
Together, the human and animal findings suggest that hypoglycemia deserves further investigation as a possible contributor to retinal complications.
Why Can Diabetic Retinopathy Sometimes Worsen After Rapid Blood Sugar Improvement?
Managing blood sugar is essential for reducing the long-term risk of diabetic complications.
However, researchers have long recognized a phenomenon called early worsening of diabetic retinopathy, which can occur in some individuals after substantial improvements in glucose control.
This effect is more likely to be a concern in certain patients who already have retinopathy, particularly when glucose levels improve rapidly.
The new research suggests that hypoglycemia-related HIF signaling might be one contributor in some circumstances.
Nevertheless, early worsening is a complex clinical phenomenon and cannot be explained entirely by low blood sugar.
Rapid reductions in average blood glucose can be associated with retinal changes even without documented hypoglycemic episodes.
The overall evidence continues to show that appropriate long-term glycemic management reduces the risk of diabetic retinopathy developing or progressing.
Therefore, people should not intentionally maintain elevated blood sugar or stop prescribed treatment out of fear of eye damage.
Instead, clinicians may monitor eye health more closely when glucose-lowering treatment is intensified, particularly in individuals with pre-existing diabetic retinopathy.
What Do the 2026 Diabetes Guidelines Recommend?
The American Diabetes Association’s Standards of Care in Diabetes—2026 continue to emphasize individualized glucose targets, prevention of hypoglycemia, and regular screening for diabetes-related complications.
These recommendations reinforce several important principles.
Stable Glucose Management Matters
HbA1c is widely used to evaluate average blood glucose over approximately two to three months.
However, HbA1c does not reveal every episode of low blood sugar or the degree of day-to-day glucose variability.
For individuals using continuous glucose monitoring (CGM), metrics such as time in range and time below range can provide additional information.
The 2026 recommendations recognize CGM as particularly useful for people at risk of hypoglycemia.
Retinal Screening Remains Essential
The guidelines recommend:
- Type 1 diabetes: Adults should generally receive an initial comprehensive dilated eye examination within five years after diabetes onset.
- Type 2 diabetes: Adults should receive an initial comprehensive dilated eye examination at diagnosis.
- Ongoing screening: Many patients require annual examinations, although intervals of one to two years may be considered when repeated examinations show no retinopathy and glycemic indicators are within the target range.
- Existing retinopathy: More frequent examinations may be necessary depending on disease severity and progression.
Patients with known diabetic retinopathy may also need reassessment when glucose-lowering treatments are intensified.
Clinical guideline: American Diabetes Association, Retinopathy, Neuropathy, and Foot Care: Standards of Care in Diabetes—2026
Glucose management guideline: ADA, Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises, 2026
Can Low Blood Sugar Cause Temporary Blurred Vision?
Yes. Hypoglycemia can cause temporary visual disturbances, including blurry or disturbed vision.
Low blood glucose affects the nervous system, including visual processing.
These immediate effects should be distinguished from diabetic retinopathy, which involves longer-term damage to retinal tissue and blood vessels.
Temporary blurred vision during a hypoglycemic episode does not automatically mean the blood-retinal barrier has been damaged.
Symptoms associated with hypoglycemia may also include:
- Sweating or trembling.
- Sudden hunger.
- Dizziness or weakness.
- Difficulty concentrating.
- Palpitations.
- Confusion.
- Visual disturbances.
Severe hypoglycemia can cause seizures, loss of consciousness, or an inability to manage the episode independently.
Anyone experiencing sudden or persistent vision loss should receive urgent medical evaluation rather than assuming that low blood sugar is the only explanation.
How Can People With Diabetes Protect Their Vision?
The most practical lesson from this research is not to avoid lowering blood glucose. It is to manage diabetes safely while minimizing dangerous glucose fluctuations.
1. Follow Individualized Blood Sugar Targets
Work with a qualified diabetes healthcare professional to establish appropriate glucose and HbA1c targets.
Targets may vary according to age, medical history, medication use, pregnancy, and risk of severe hypoglycemia.
2. Recognize and Treat Hypoglycemia Promptly
For many people with diabetes, blood glucose below 70 mg/dL (3.9 mmol/L) is considered low and requires attention.
For an alert person who can swallow safely, a commonly recommended approach is to consume approximately 15 grams of fast-acting carbohydrate, wait 15 minutes, and recheck glucose, repeating as necessary according to their diabetes care plan.
Severe hypoglycemia may require emergency assistance and glucagon. Food or drink should never be given by mouth to someone who is unconscious or cannot swallow safely.
3. Consider Continuous Glucose Monitoring When Appropriate
CGM devices can provide glucose trends and alerts for low blood sugar.
For eligible patients, these tools can help identify patterns that are difficult to recognize from occasional finger-prick measurements alone.
CGM does not eliminate the need for clinical judgment or individualized medication management.
4. Attend Regular Dilated Eye Examinations
Diabetic retinopathy may develop without early symptoms.
An eye care professional can identify retinal abnormalities and recommend treatment before substantial vision loss occurs.
5. Manage Blood Pressure and Other Risk Factors
Maintaining appropriate blood pressure and lipid levels, avoiding smoking, following prescribed treatment, and addressing other diabetes-related complications can support long-term eye health.
6. Seek Assessment for New Visual Symptoms
Persistent blurred vision, new floaters, dark areas in vision, or other unexplained visual changes should be assessed by an eye care professional.
Sudden vision loss, a new curtain-like shadow, or rapidly developing visual disturbances require urgent medical attention.
October 2026 Research Update: What Has Changed?
The 2025 discovery has contributed to a broader discussion about how glucose variability and hypoglycemia may influence diabetic eye disease.
A commentary published in JAMA Ophthalmology on October 23, 2025, titled Beyond Hemoglobin A1c Hypoglycemia, Glycemic Patterns, and Risk of Diabetic Retinopathy, highlighted the limitations of relying on HbA1c alone when evaluating glucose-related complications.
HbA1c remains an important measure of diabetes management, but it cannot fully describe glucose fluctuations or the frequency of low blood sugar episodes.
The discussion reinforces the importance of examining patterns of glucose exposure alongside established risk factors.
Read the commentary: JAMA Ophthalmology, Beyond Hemoglobin A1c
The ADA’s 2026 recommendations similarly emphasize glucose monitoring, hypoglycemia prevention, and individualized treatment.
However, these recommendations should not be interpreted as clinical endorsement of experimental HIF inhibitors for diabetic retinopathy.
As of this update, the evidence described here does not establish that 32-134D prevents retinal disease or vision loss in humans.
Could HIF Inhibitors Become Future Treatments for Diabetic Retinopathy?
The experimental findings suggest that HIF signaling may be a potential therapeutic target.
Because HIF proteins regulate numerous cellular responses, blocking their activity may influence multiple molecules involved in retinal blood vessel leakage.
This could offer an alternative research strategy to treatments that target individual downstream pathways.
However, several important challenges remain.
First, the optimal level of HIF inhibition must be established, since these proteins also participate in normal biological functions.
Second, researchers must determine whether treatment can safely prevent clinically meaningful retinal damage.
Third, the benefits and risks must be assessed in human clinical trials.
Until such studies are completed, HIF inhibition with 32-134D should be regarded as an experimental approach rather than an available treatment.
What Treatments Are Currently Available?
Established treatments for diabetic retinopathy and diabetic macular oedema can include:
- Injections of anti-VEGF medications for appropriate indications.
- Other intraocular medications in selected cases.
- Retinal laser treatment.
- Vitrectomy surgery for certain advanced complications.
- Ongoing management of glucose, blood pressure, and other systemic risk factors.
Treatment depends on the stage and type of retinal disease.
An ophthalmologist can determine which interventions are appropriate.
For more information, see the National Eye Institute’s diabetic retinopathy treatment guide.
Study Limitations: What We Still Don’t Know
Although the findings are promising, several limitations should guide their interpretation.
Animal models are not the same as human disease. Most of the direct evidence linking hypoglycemia, HIF signaling, and retinal barrier breakdown in this study came from diabetic mice.
Temporary vascular changes do not necessarily equal permanent vision loss. The experiments measured molecular and vascular responses rather than demonstrating long-term visual outcomes in human patients.
The effects of different hypoglycemia patterns remain uncertain. More research is needed to understand how episode duration, severity, frequency, and pre-existing retinal disease influence risk.
The experimental treatment has not been clinically validated. The findings involving 32-134D do not establish safety, effectiveness, or an appropriate treatment regimen for patients.
Low blood sugar is not the only cause of diabetic eye disease. Chronic hyperglycemia, disease duration, blood pressure, and other factors remain central to diabetic retinopathy risk.
These limitations reinforce the need for appropriately designed human studies before research findings are translated into routine treatment decisions.
Conclusion
The discovery that low blood sugar can activate HIF signaling and weaken the retinal blood-vessel barrier in diabetic mice adds an important piece to our understanding of diabetic eye disease.
For decades, chronic high blood sugar has been recognized as a major cause of diabetic retinopathy. The new research suggests that glucose fluctuations, including hypoglycemia, may also influence retinal vascular health.
The experimental compound 32-134D offers a potential direction for future treatment research, but its effectiveness in humans remains unproven.
The most important message is that protecting vision requires safe, consistent diabetes management, not simply reducing blood sugar as much as possible.
Combining individualized glucose targets, hypoglycemia prevention, regular eye screening, and established treatments remains the most evidence-based approach to reducing diabetes-related vision loss.
References
- Guo, C., et al. (2025). Hypoglycemia Promotes Inner Blood-Retinal Barrier Breakdown and Retinal Vascular Leakage in Diabetic Mice. Science Translational Medicine, 17(796), eadq5355.
https://doi.org/10.1126/scitranslmed.adq5355 - National Eye Institute (May 6, 2025). NEI-Funded Study Shows Low Blood Sugar Contributes to Eye Damage and Vision Loss in Diabetic Retinopathy.
https://www.nei.nih.gov/research-and-training/research-news/nei-funded-study-shows-low-blood-sugar-contributes-eye-damage-and-vision-loss-diabetic-retinopathy - Johns Hopkins Medicine (May 6, 2025). Low Blood Sugar Contributes to Eye Damage and Vision Loss in Diabetic Retinopathy; Experimental Drug May Help Treat Condition.
https://www.hopkinsmedicine.org/news/newsroom/news-releases/2025/05/low-blood-sugar-contributes-to-eye-damage-and-vision-loss-in-diabetic-retinopathy-experimental-drug-may-help-treat-condition - Tysoe, O. (2025). Hypoglycaemia Exacerbates Diabetic Retinopathy via HIF Accumulation. Nature Reviews Endocrinology, 21, 396.
https://doi.org/10.1038/s41574-025-01136-6 - González-Saldivar, G., et al. (2023). Retinal Microvascular Density and Perfusion During an Insulin-Induced Hypoglycemia Episode: A Warning Call.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10593551/ - Giacalone, J. C., & Barkmeier, A. J. (2025). Beyond Hemoglobin A1c—Hypoglycemia, Glycemic Patterns, and Risk of Diabetic Retinopathy. JAMA Ophthalmology.
https://doi.org/10.1001/jamaophthalmol.2025.3933 - American Diabetes Association (2026). Retinopathy, Neuropathy, and Foot Care: Standards of Care in Diabetes—2026. Diabetes Care.
https://doi.org/10.2337/dc26-s012 - American Diabetes Association (2026). Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes—2026.
https://doi.org/10.2337/dc26-s006 - National Eye Institute. Diabetic Retinopathy: Causes, Symptoms, Diagnosis, and Treatment.
https://www.nei.nih.gov/eye-health-information/eye-conditions-and-diseases/diabetic-retinopathy