Fibromyalgia is frequently accompanied by autonomic nervous system dysfunction, often characterized by sympathetic predominance. Alterations in ocular microcirculation have been reported in the presence of autonomic dysfunction, including potential reductions in choroidal vascular parameters. This observational study aims to examine the association between autonomic symptom burden and the choroidal vascularity index (CVI), a quantitative marker of choroidal vascular structure derived from optical coherence tomography (OCT), in individuals with fibromyalgia compared with age- and sex-matched healthy controls.

This is a cross-sectional, observational case-control study planned to investigate the relationship between autonomic nervous system dysfunction and choroidal vascularity index (CVI) in patients diagnosed with fibromyalgia according to the 2016 American College of Rheumatology (ACR) criteria. Participants will include adult females and males aged 18-50 years. Demographic and clinical data will be collected, including age, sex, body mass index (BMI), and disease duration.

Autonomic symptom burden will be assessed using the Composite Autonomic Symptom Score 31 (COMPASS-31). Fibromyalgia severity and its impact on daily functioning will be measured using the Revised Fibromyalgia Impact Questionnaire (FIQR). Central sensitization symptoms will be evaluated with the Central Sensitization Inventory (CSI).

All participants will undergo choroidal imaging using optical coherence tomography (OCT; Heidelberg Engineering, Heidelberg, Germany). CVI will be calculated as the ratio of luminal area to total choroidal area. To reduce operator-dependent variability, CVI quantification will be performed using an open-access artificial intelligence-assisted tool designed for choroidal layer analysis (ChoroidAI / choroidometer.com), with standardized image acquisition conditions.

Primary analyses will compare CVI between the fibromyalgia and control groups and evaluate associations between CVI and autonomic symptom burden, fibromyalgia impact, and central sensitization measures.

Inclusion Criteria:

• Age 18-50 years, female or male
• Fibromyalgia group: diagnosis of fibromyalgia according to 2016 ACR criteria
• Ability and willingness to provide written informed consent
• Adequate ocular media clarity suitable for OCT imaging
• Control group: age- and sex-matched healthy volunteers

Exclusion Criteria:

• Ocular exclusions: cataract or other media opacity; glaucoma or optic nerve disease; ocular surface disorders (e.g., dry eye disease); retinal diseases (e.g., diabetic retinopathy, macular disease); ocular surgery or eye/head trauma within the last 3 months; best-corrected visual acuity < 20/20; refractive error > ±3.00 diopters; intraocular pressure > 21 mmHg; use of topical ophthalmic medications
• Systemic/neurologic exclusions: diabetes mellitus; hypertension; hyperlipidemia; thyroid disorders; inflammatory rheumatic/autoimmune diseases; polyneuropathy or neurodegenerative disease; major depressive disorder or anxiety disorder; heavy smoking (>20 cigarettes/day); alcohol or substance dependence; excessive caffeine intake (>2.5 cups/day)

Adults aged 18-50 years with fibromyalgia and matched healthy controls recruited from Prof. Dr. Cemil Taşcıoğlu City Hospital in Istanbul, Turkey.

De-identified individual participant data (IPD) underlying the results reported in the primary publication (including COMPASS-31, FIQR, CSI scores and OCT-derived CVI measurements) will be shared upon reasonable request. All shared data will be anonymized/de-identified and will not include any direct identifiers.