A 2026 cross-sectional study found that tear vitamin D levels are 43% lower in keratoconus patients compared to healthy people, and vitamin D deficiency worsens as the disease progresses. According to Gram Research analysis, when researchers combined vitamin D measurements with two other tear markers—inflammation and antioxidant protection—they could identify keratoconus with 94% accuracy. While these findings suggest a simple tear test might eventually help detect and monitor keratoconus, the research is exploratory and requires confirmation in larger studies before clinical use.
Researchers discovered that people with keratoconus—a condition where the cornea thins and bulges—have significantly lower levels of vitamin D in their tears. According to Gram Research analysis, this exploratory study found that tear vitamin D was 43% lower in keratoconus patients compared to healthy people, and the deficiency got worse as the disease progressed. Scientists also identified two other markers in tears—reduced antioxidant protection and increased inflammation—that together created a molecular signature matching disease severity with 94% accuracy. While these findings are promising for developing a simple tear-based test to detect and monitor keratoconus, researchers emphasize the results need confirmation in larger studies before clinical use.
Key Statistics
A 2026 cross-sectional study of 63 participants found tear vitamin D was 43% lower in keratoconus patients (18.5 ng/mL) compared to healthy controls (32.4 ng/mL), with a 72% reduction in the most severe disease stage.
According to research reviewed by Gram, a combination of three tear markers—vitamin D, inflammation (IL-6), and antioxidant protection (NRF2)—achieved 94% accuracy in distinguishing keratoconus patients from healthy controls in a 2026 exploratory study.
A 2026 study found that antioxidant protection (NRF2) was detectable in only 35.7% of keratoconus tear samples versus 74.3% in healthy controls, declining to 0% in stage IV disease.
Research from 2026 suggests that approximately 48% of vitamin D’s association with keratoconus severity may work through inflammation pathways, while 52% appears to be a direct effect.
The Quick Take
- What they studied: Whether vitamin D levels in tears could help identify keratoconus and track how severe the condition is
- Who participated: 28 people with keratoconus and 35 healthy controls. The keratoconus group included people who rub their eyes frequently and have allergies, which are risk factors for the disease
- Key finding: Tear vitamin D was 43% lower in keratoconus patients (18.5 vs 32.4 ng/mL), and it dropped dramatically as disease severity increased—by 72% in the most advanced stage. A combination of three tear markers correctly identified keratoconus 94% of the time
- What it means for you: A simple tear test might one day help eye doctors catch keratoconus earlier and monitor how it’s progressing. However, this is early-stage research, and larger studies are needed before doctors can use this test clinically
The Research Details
This was an exploratory cross-sectional study, meaning researchers collected tear samples from keratoconus patients and healthy people at one point in time and compared them. Tears were collected using standardized strips, and researchers measured three key markers: vitamin D levels, inflammation proteins (IL-6), and antioxidant protection (NRF2). They used advanced lab techniques to measure these markers and then analyzed whether they correlated with disease severity using a staging system called ABCD.
The researchers also performed statistical analyses to understand how these markers work together. They tested whether vitamin D’s connection to disease severity was direct or worked through inflammation. They also calculated how accurately a combination of all three markers could distinguish keratoconus patients from healthy controls.
This research approach is important because keratoconus currently lacks reliable tear-based biomarkers that track disease severity. Most diagnosis relies on imaging machines, which are expensive and not always available. A tear test would be simple, inexpensive, and could be repeated easily to monitor disease progression. Understanding the biological mechanisms—like vitamin D deficiency and inflammation—could also lead to new treatments.
This is an exploratory study with a relatively small sample size (63 total participants), so results should be viewed as hypothesis-generating rather than definitive. The researchers were transparent about this limitation. The study was well-designed with standardized collection methods and appropriate statistical techniques. However, because it’s cross-sectional, it shows associations but cannot prove that vitamin D deficiency causes keratoconus or that it causes the inflammation. The researchers acknowledge these limitations and call for larger, longer-term studies to confirm findings.
What the Results Show
Tear vitamin D levels were dramatically lower in keratoconus patients compared to healthy controls: 18.5 ng/mL versus 32.4 ng/mL—a 43% reduction. More importantly, within the keratoconus group, vitamin D levels dropped progressively as disease severity increased, with the strongest correlation to Kmax (a measure of corneal curvature; r=-0.72) and disease stage (r=-0.68). By stage IV (the most severe), vitamin D had dropped 72% from baseline levels.
The researchers also found that antioxidant protection (measured by NRF2 detectability) was significantly reduced in keratoconus patients: only 35.7% of keratoconus samples showed detectable NRF2 compared to 74.3% in healthy controls. This protection declined steadily with disease progression, disappearing entirely in stage IV disease.
When the researchers combined all three markers—vitamin D, inflammation (IL-6), and antioxidant protection (NRF2)—into a single “Molecular Tear Score,” it could distinguish keratoconus patients from healthy controls with 94% accuracy (AUC 0.94). Even after statistical correction for potential bias, accuracy remained strong at 91%.
The analysis suggested that vitamin D’s relationship to disease severity may work partially through inflammation: about 48% of vitamin D’s association with disease severity appeared to be mediated by IL-6 inflammation, while 52% was a direct effect. This suggests vitamin D deficiency might contribute to keratoconus through multiple pathways. The study also confirmed that the cohort had high rates of eye rubbing and allergies, which are known risk factors for keratoconus, making the findings particularly relevant to this high-risk population.
This is one of the first studies to systematically examine vitamin D in keratoconus tears and to create a multi-marker tear signature for disease severity. Previous research has suggested vitamin D plays a role in corneal health and that inflammation is involved in keratoconus, but this study provides the first quantitative tear-based evidence linking vitamin D deficiency, reduced antioxidant protection, and inflammation in a severity-graded manner. The 94% diagnostic accuracy is promising compared to other proposed biomarkers, though direct comparisons aren’t available.
This study has several important limitations. First, it’s small (only 63 participants) and cross-sectional, so it cannot prove cause-and-effect relationships. Second, the keratoconus group was enriched for eye rubbing and allergies, so results may not apply to all keratoconus patients. Third, the study is exploratory and hypothesis-generating—the researchers explicitly state these findings need confirmation in larger, longer-term studies. Fourth, temporal directionality cannot be determined: we don’t know if vitamin D deficiency causes keratoconus or if keratoconus causes vitamin D deficiency. Finally, the study didn’t measure vitamin D intake or sun exposure, which could influence tear vitamin D levels.
The Bottom Line
These findings are too preliminary for clinical recommendations at this time. However, they suggest that maintaining adequate vitamin D status may be worth investigating as a potential preventive or supportive strategy for keratoconus, particularly in people with risk factors like frequent eye rubbing or allergies. Anyone with keratoconus should discuss vitamin D status with their eye doctor, but this research alone doesn’t warrant routine supplementation without medical guidance. Confidence level: Low to Moderate (exploratory findings requiring confirmation).
People with keratoconus or family history of the condition should be aware of these findings. Eye care professionals may find this research relevant for future diagnostic development. People with allergies and frequent eye rubbing—risk factors for keratoconus—might consider discussing vitamin D status with their doctors. This research is NOT yet ready for self-diagnosis or self-treatment decisions.
If these findings are confirmed and developed into a clinical test, it would likely take 3-5 years minimum before such a test becomes available in clinical practice. Any benefits from vitamin D optimization would likely take weeks to months to manifest, though this hasn’t been studied yet.
Frequently Asked Questions
What is keratoconus and why does vitamin D matter for this eye condition?
Keratoconus is a progressive eye disease where the cornea thins and bulges into a cone shape, causing blurred vision. A 2026 study found tear vitamin D is 43% lower in keratoconus patients, suggesting vitamin D deficiency may contribute to disease development or progression through inflammation and reduced antioxidant protection.
Can I use a tear vitamin D test to diagnose keratoconus right now?
Not yet. While a 2026 exploratory study achieved 94% diagnostic accuracy combining three tear markers, researchers emphasize these findings are hypothesis-generating and require confirmation in larger studies before clinical application. Talk to your eye doctor about current diagnostic options.
Should I take vitamin D supplements if I have keratoconus?
This research doesn’t yet support routine supplementation for keratoconus. A 2026 study found lower tear vitamin D in keratoconus patients, but the study was exploratory and cross-sectional. Discuss vitamin D status with your eye doctor and primary care physician before starting supplements.
How does eye rubbing relate to the vitamin D findings in keratoconus?
This 2026 study enrolled keratoconus patients with frequent eye rubbing and allergies—known risk factors. The research doesn’t explain the connection between rubbing and vitamin D, but suggests investigating vitamin D status in high-risk populations with these habits may be worthwhile.
What’s the next step for this keratoconus tear test research?
Researchers call for larger, longer-term studies in diverse keratoconus populations to confirm these 2026 findings. If validated, a tear-based test could eventually provide a simple, inexpensive way to detect and monitor keratoconus progression compared to current imaging methods.
Want to Apply This Research?
- Track daily vitamin D intake (from food and supplements in IU), sun exposure time, and eye rubbing frequency. Users could log these weekly and correlate with any changes in keratoconus symptoms or contact lens prescription changes if applicable.
- Users at risk for keratoconus could set reminders to: (1) limit eye rubbing by using cold compresses instead, (2) track vitamin D-rich foods consumed, and (3) monitor sun exposure. The app could provide alerts when vitamin D intake falls below recommended levels.
- Establish a baseline of current vitamin D intake and eye rubbing habits. Set a 12-week tracking period to monitor whether reducing eye rubbing and optimizing vitamin D intake correlates with subjective improvements in eye comfort or stability of contact lens prescription. Share results with eye care provider for professional interpretation.
This article summarizes exploratory research findings and is not medical advice. Keratoconus is a serious eye condition requiring professional diagnosis and management by an eye care specialist. The tear vitamin D test described in this research is not yet available for clinical use. Do not start, stop, or change any vitamin D supplementation or keratoconus treatment based on this article without consulting your eye doctor or primary care physician. If you have symptoms of keratoconus (blurred or distorted vision, frequent changes in eyeglass prescription, eye irritation or swelling), seek immediate evaluation from an ophthalmologist or optometrist.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.