**Background:** Omega-3 polyunsaturated fatty acids (PUFAs), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have anti-inflammatory and neuroprotective properties. Corneal nerve loss occurs early in diabetic peripheral neuropathy, and corneal nerve parameters are validated surrogate markers of neuropathy. Preclinical and clinical studies suggest omega-3 supplementation can promote corneal nerve regeneration, but the relationship between basal systemic omega-3 levels and corneal nerve health was unclear. This study aimed to evaluate the association between systemic fatty acid levels and corneal nerve structure and function.
**Methods:** This prospective, cross-sectional study enrolled 47 participants (26 with diabetes, 21 without) aged ≥18 years with Norfolk QoL-DN scores <16. Exclusion criteria included rigid contact lens wear, active ocular infection/inflammation (except mild dry eye), corneal abnormalities, neuropathy from non-diabetic causes, and best corrected visual acuity <6/12. Ocular surface assessments included OSDI, tear osmolarity (TearLab), tear break-up time, corneal and conjunctival staining (Oxford scale), and slit lamp grading (Efron scale). Corneal sensation was measured using a non-contact esthesiometer with room-temperature (23–24°C) and cooled (18–19°C) air stimuli at central and peripheral cornea. Corneal sub-basal nerve plexus parameters (CNFL, CNFD, CNBD, CTBD) were quantified from IVCM images using ACCMetrics (central) and NeuronJ (peripheral). Corneal immune cells were classified into three morphological phenotypes. Systemic fatty acid profiles were analyzed from dried blood spots, including EPA, DHA, arachidonic acid (AA), total omega-3 and omega-6 levels, and the Omega-3 Index (% of EPA+DHA in erythrocyte membranes). Multiple linear regression models adjusted for age, sex, Norfolk QoL-DN score, diabetes status, and dry eye disease. Sample size (n=47) was based on an estimated correlation coefficient of 0.40 with 80% power at α=0.05.
**Key Results:** The median Omega-3 Index was 5.21% (IQR: 4.44–5.94%). Mean CNFL was 13.53±3.37 mm/mm². In multiple linear regression, Omega-3 Index (β=0.33; p=0.017), age (β=−0.46; p=0.001), and diabetes (β=−0.30; p=0.030) were independently associated with CNFL (R²=0.36, p<0.0001). DHA level was also positively associated with CNFL (β=0.32; p=0.027) in a separate model (R²=0.37, p=0.003). Neither EPA nor total omega-6 levels were associated with CNFL. Similar associations were found for CNFD: Omega-3 Index (β=0.35; p=0.014), age (β=−0.44; p=0.001), and diabetes (β=−0.27; p=0.054) (R²=0.36, p=0.004); DHA (β=0.37; p=0.013) and age (β=−0.39; p=0.005) were associated with CNFD (R²=0.36, p=0.004). No associations were found between PUFA levels and corneal sensation thresholds or corneal immune cell density. In the diabetes subgroup, CNFL was negatively correlated with cooled stimulus thresholds in central (ρ=−0.50; p=0.009) and peripheral (ρ=−0.50; p=0.01) cornea, but not in controls.
**Clinical Implications:** This study demonstrates a positive, independent association between systemic omega-3 PUFA levels (particularly DHA) and corneal nerve structure, suggesting that dietary omega-3 intake may influence corneal nerve health. The findings support the potential for omega-3 supplementation as a therapeutic strategy to preserve or improve corneal nerve architecture, especially in individuals with diabetes. The altered structure-function relationship to cold stimuli in diabetes may reflect early dysfunction of TRPM8-expressing cold thermoreceptors. The median Omega-3 Index of 5.2% is below the 8–11% target recommended for cardiovascular health, indicating that many individuals may benefit from increased omega-3 intake. Limitations include the cross-sectional design, small sample size, and use of a symptom questionnaire rather than neurophysiological measurements for neuropathy classification. Future longitudinal studies with a wider range of Omega-3 Index scores are needed to determine optimal thresholds for corneal nerve health.