This is a cross-sectional and comparative study carried out in a tertiary education and research hospital’s Physical Medicine and Rehabilitation and Ophthalmology clinics. All patients in the study were diagnosed at the outpatient clinic for physical medicine and rehabilitation. The date range in which the article was conducted is January 2024 and May 2024. Only individuals who satisfied the 2016 American College of Rheumatology (ACR) criteria were enrolled in the FMS group [14]. The study comprised individuals over 18 who consented to participate and involved healthy controls aligned with the patient group’s baseline characteristics. Newly diagnosed individuals were included in the study, whereas those receiving FMS-related drugs were excluded. Exclusion criteria comprise dementia, glaucoma, retinal disorders, uveitis, iridocyclitis, cardiovascular diseases, hypertension, diabetes mellitus, inflammatory rheumatic diseases, autoimmune diseases, vasculitis, neurological diseases, prior ophthalmic operations, and drug use that can have an impact on outcomes. All participants underwent routine blood tests. Individuals who did not fulfill the specific requirements for the research were excluded from participating in the study. An evaluation was conducted on the hospital registry system to ascertain whether the individuals fulfilled the exclusion criteria. The Ministry of Health system was utilized to authenticate prescription medications.

Data on the participants’ age, sex, body mass index (BMI), duration of symptoms, occupational status, and educational status were obtained. The same physical medicine and rehabilitation specialist and ophthalmologist conducted the clinical screenings, OCT and OCTA measurements, and further examinations. The Fibromyalgia Impact Questionnaire (FIQ) was used to evaluate the severity of the condition.

The FIQ is a thorough instrument specifically developed to evaluate the entire influence of FMS on a patient’s daily life. The FIQ was initially created by Burckhardt et al. [15] in 1991 and has gained widespread acceptance as a standard tool in clinical and research environments for assessing FMS severity. It has been demonstrated that the Turkish version of the FIQ is reliable and valid [16]. There are ten fundamental questions included in the questionnaire. A score of 100 is the highest possible, and higher values indicate a more severe health issue.

An automatic computer algorithm determines RNFL thickness without needing a user or reference plane. The measurements are displayed as a thickness map according to the position of the RNFL around the optic disc: 12 clock quadrants, four quadrants, and the average RNFL thickness. For these measurements to be reliable, the 3.4 mm diameter circle must be placed around the optic disc equidistant from all quadrants. In the newer systems, the device automatically provides the ring placement without user intervention.

In SD-OCT devices, numerical data are given in disc area, mean cup volume, vertical and mean C/D ratios, RNFL quadrant thickness, mean RNFL thickness, and neuroretinal rim area. These data are compared with normative data prepared according to racial variation and age in the device memory, and the deviations from the parameters considered normal are shown with color-coded maps. White and green bands indicate typical values, and yellow borderline and red abnormal values. In the healthy population, 5% are in the white band above the green, 90% in the green band, 4% in the yellow band, and 1% in the red band [17].

After achieving mydriasis, the OCT-RNFL test was evaluated with Zeiss Cirrus HD-OCT Model 4000 using an Optic Disc Cube 200 × 200 module. Care was taken to ensure that the signal strength was more than 5/10. Mean retinal nerve fiber thickness (in µm) on the Optic Disc Cube 200 × 200 module and nerve fiber thickness in 4 quadrants were taken as the basis.

OCTA is a noninvasive new-generation imaging system that provides detailed visualization of vascular structures by detecting the motion contrast of blood in the posterior segment vessels without using fluorescein. The first step in obtaining the image on the OCTA device is detecting motion contrast. Secondly, consecutive B-scans are taken, and the differences between the images are detected. In the last step, this information is processed by the software program to create an image of the retinal vascular structures. Meanwhile, the device software corrects motion artifacts caused by eye movements [18].

The OCTA device detects motion contrast in the posterior segment tissues and calculates the signal difference between static and nonstatic tissues. This creates three-dimensional image cubes from the en-face images of the retina, choroid, and optic nerve. The device’s segmentation feature allows for analyzing these image cubes in layers.

The most common scan sizes in OCTA are 3 × 3 mm and 6 × 6 mm. The detail decreases as the examined area increases. In our study, after sufficient mydriasis was achieved in the patients, the same personnel performed OCTA measurements using an AngioVue (Optovue Inc, Fremont, CA, USA) SD-OCT (spectral domain optical coherence tomography) device. The wavelength used in the device is 840 nm, axial resolution is 5 microns, transverse resolution is 15 microns, and scan rate (A scan/sec) is 70 kHz. All participants were evaluated with 3 × 3 images and OCTA images with scan quality below 8; segmentation artifacts, motion artifacts, and projection artifacts were excluded from the study.

Foveal avascular zone area (mm2), foveal avascular zone perimeter (mm), and foveal density (%) were measured automatically with the device’s phase assessment tool. Density assessment tool measured vascular density (%) in the area (fovea, parafovea) divided by circles of 1 mm and 3 mm diameter with foveal avascular zone as the center of superficial and deep capillary plexus. Each segment was divided into four equal quadrants: temporal, superior, nasal, and inferior. With the flow assessment tool, blood flow in the outer retina and choriocapillaris was recorded in mm2 in an area with a central radius of 1 mm and an area of 3.142 mm2.

Measures were conducted for both eyes; however, only the data from the right eye were used in the statistical analysis. OCTA and RNFL assessments are visualized in Figs. 1, 2 and 3.

Superficial vascular density assessment using optical coherence tomography angiography

Deep vascular density assessment using optical coherence tomography angiography

Retinal nerve fiber layer thickness assessment

The local Research Ethics Committee approved this study after thoroughly evaluating the ethical considerations (approval date: 07.12. 2023 and number: 2999). Additionally, written consent was obtained from all participants. The Helsinki principles were followed consistently throughout the entire investigation.

Data analysis was performed using SPSS vn 23 software. Results were presented as a number, percentage, mean ± standard deviation, and median (minimum-maximum). The decision on the conformity of the data to normal distribution was based on the results of the Shapiro-Wilk test. Continuous variables were compared between groups using the Independent Sample t-test and the Mann-Whitney U-test. The chi-square test was also used for categorical variable comparisons. Correlations were evaluated using Pearson and Spearman rho tests. p < 0.05 was considered statistically significant.