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The eye is a measurement surface.
The claims are not interchangeable.
Retina, external-eye photography, pupil dynamics and iris morphology are different evidence layers. This page keeps the published findings attached to the modality that produced them.
Neural, vascular and visible.
The eye gives non-invasive access to structures tied to the nervous and vascular systems. That makes ocular imaging scientifically interesting—but it does not make every ocular feature a validated biomarker.
Ocular imaging ↔ systemic signals
Strongest published evidence currently comes from retinal fundus imaging, OCT and external-eye photography—not from conventional iris organ mapping.
Cardiovascular risk factors from retinal photographs
Deep learning predicted age, sex, smoking status and systolic blood pressure from retinal fundus images. Major adverse cardiac events were classified at AUC 0.70 in the reported validation analysis.
Open paper ↗EXTERNAL EYE · NATURE BIOMEDICAL ENGINEERING · 2022Poor glucose control from photographs of the front of the eye
The model was validated in 48,644 additional patients. For HbA1c ≥9%, reported AUCs across four validation sets were 0.700, 0.734, 0.693 and 0.676. Elevated lipids were explored separately.
Open paper ↗RETINAL VESSELS · NATURE BIOMEDICAL ENGINEERING · 2020Retinal-vessel calibre and cardiovascular risk
Automated vessel-calibre measurements showed high agreement with expert graders (ICC 0.82–0.95) and were associated with blood pressure, BMI, total cholesterol, HbA1c and incident cardiovascular disease.
Open paper ↗OCULOMICS · NATURE CARDIOVASCULAR RESEARCH · 2026Ophthalmic imaging linked to cardiovascular and neurological traits
A UK Biobank multi-omic analysis found retinal imaging representations associated with ischemic heart disease, cerebrovascular disease, Parkinson’s disease and dementia, including prospective disease associations.
Open paper ↗RETINAL VASCULATURE · TROMSØ EYE STUDY · 2013Retinal vessel calibre tracked established cardiovascular risk factors
Arteriolar calibre was associated with blood pressure, HbA1c and smoking; venular calibre was associated with blood pressure, BMI, HDL/LDL cholesterol and smoking in this population-based study.
Open paper ↗RETINAL VASCULATURE · MESA · 2006Microvascular calibre reflected metabolic and inflammatory context
Retinal arteriolar and venular calibre were associated with hypertension, diabetes, obesity and dyslipidaemia. Venular calibre was also associated with inflammatory markers.
Open paper ↗RETINAL VASCULATURE · EPIC-NORFOLK · 2018Tortuosity and vessel width tracked cardiometabolic traits
Venular tortuosity was associated with BMI, HbA1c and type 2 diabetes; arteriolar tortuosity was associated with age and systolic blood pressure.
Open paper ↗RETINAL AGE · NATURE COMMUNICATIONS · 2026Retinal age gap and systemic aging
A retinal foundation-model age estimate achieved a mean absolute error of 2.85 years. Retinal age gap was associated with cardiometabolic traits, cognition, mortality, dementia and incident cardiovascular disease.
Open paper ↗Pupil response ↔ cognition + autonomic function
Pupillometry measures a dynamic physiological response. Research spans light reflex, autonomic function, attention, cognitive effort and working memory. Clinical use still depends on calibrated acquisition and validated protocols.
Light-reflex dynamics in Parkinson’s disease
Eleven studies entered meta-analysis. Parkinson’s groups showed significantly reduced maximum constriction velocity and amplitude, with longer constriction latency. The authors stress protocol heterogeneity and the need for standardisation.
Open paper ↗MCI · PROSPECTIVE COHORT · 2024Task-evoked pupil response in mild cognitive impairment
The study included 213 participants with MCI and 514 cognitively normal controls. MCI participants showed reduced pupil dilation during cue and target-onset periods in oculomotor cognitive tasks.
Open paper ↗DEMENTIA / MCI · SCOPING REVIEW · 2023Pupil response during cognitive tasks
Across the included literature, task-evoked pupillary responses differed between cognitively impaired and healthy groups. Reduced dilation was reported in Alzheimer’s disease; evidence in MCI remained less consistent.
Open paper ↗WORKING MEMORY · REVIEW · 2024Encoding, maintenance and prioritisation
A review of visual working-memory research describes pupil dynamics across encoding, maintenance and prioritisation, and discusses relationships between pupil size and memory performance.
Open paper ↗ALZHEIMER’S DISEASE · PROOF-OF-CONCEPT · 2024Quantitative light-reflex pupillometry in dementia
A university memory-clinic study reported AUROC values of 0.74–0.81 for models distinguishing Alzheimer’s disease from healthy controls and other dementias. It remains proof-of-concept rather than a stand-alone diagnostic test.
Open paper ↗COGNITIVE PUPILLOMETRY · METHODS REVIEW · 2023Measurement is powerful; methodology still varies
Cognitive pupillometry is used to study attention, mental effort and working memory, but experimental design and preprocessing are not yet standardised across research groups.
Open paper ↗LC–NE / CORTICAL PLASTICITY · REVIEW · 2023Pupil dynamics as a window into arousal and neuromodulation
A review links pupil-size variation with arousal, attention and mental effort, discussing the locus-coeruleus noradrenergic system as a key physiological pathway behind these effects.
Open paper ↗COGNITIVE LOAD · EXPERIMENTAL STUDY · 2026Pupil dilation changed with increasing cognitive load
Under higher-load conditions, older adults showed reduced pupillary reactivity; pupil dilation also correlated with age and Stroop interference in the reported sample.
Open paper ↗Iris structure ↔ measurable morphology
Here the evidence is about anatomy, morphology, genetics and ocular geometry. It is a different evidence class from retinal systemic biomarkers and from cognitive pupillometry.
Crypts, furrows and pigmentation have measurable genetic associations
Replicated associations linked crypt frequency with SEMA3A, contraction furrows with TRAF3IP1 and the peripupillary pigmented ring with SLC24A4. These are morphology/genetics findings—not systemic-disease maps.
Open paper ↗IRIS SURFACE · SSOCT · 2016Surface features correlated with iris volume and curvature
Higher crypt grade was associated with smaller iris volume, while darker irides and higher furrow grade were associated with larger iris volume in Asian eyes.
Open paper ↗IRIS SURFACE · STANDARDISED GRADING · 2014Crypts and furrows can be graded with reproducible agreement
The study reported strong intragrader agreement and intergrader weighted κ values of 0.775 for crypts and 0.836 for furrows, alongside associations with iris thickness.
Open paper ↗IRIS MORPHOLOGY · POPULATION STUDY · 2016Iris surface-feature frequency differs across populations
Fuchs’ crypts, Wolfflin nodules, pigment spots, contraction furrows and conjunctival melanosis showed population-dependent frequency differences across East Asian, European and South Asian groups.
Open paper ↗IRIS / CAD · EXPLORATORY ML · 2023A small iris–coronary-disease study reported high classification accuracy
The proof-of-concept study included 94 participants with CAD and 104 controls and reported 93% SVM accuracy. It is a single small study and does not establish clinical validity or validate iridology.
Open paper ↗Iris morphology stays a research question.
IRISPECTRA can measure visible structure from calibrated iris photographs. Published retinal, external-eye and pupillometry findings do not validate disease, organ or personality inference from iris zones. Any iris-specific systemic association must be tested independently against clinical ground truth.