This observational cross-sectional study was conducted in patients with sarcoidosis. Patients with the International Classification of Disease (ICD10) codes for sarcoidosis (i.e., D86*) were identified in medical journal files from the Department of Rheumatology, Department of Respiratory Medicine, or Department of Opthalmology at Odense University Hospital (OUH), Denmark, between 2008 and 2019. First, we focused on patients with OS or NS. Second, as a sarcoidosis control group, we used sarcoidosis patients without OS and NS. We were aiming at approximately 100 patients in the cohort.

The inclusion criteria comprised adult patients with an age above 18 years, a biopsy showing granulomatous inflammation, and symptoms consistent with sarcoidosis by the American Thoracic Society and European Respiratory Society [20]. To focus on exclusive sarcoidosis retinal layer changes, weexcluded patients with medically treated diabetes, non-sarcoidosis-related ocular and CNS diseases, retinal granulomas, and patients with poor image quality on OCT.

OS was defined as known uveitis within the last ten years based on the Revised Criteria of the International Workshop on Ocular Sarcoidosis (IWOS) [21] and the Standardization of Uveitis Nomenclature (SUN) [22] or a history of vision-impairing optic neuropathy. All NS patients fulfilled the probable or definite NS criteria defined by the Neurosarcoidosis Consortium Consensus group (NCCG) [5].

All patients were examined at the Department of Ophthalmology, OUH.

The outcome variables were CMT, RT, RNFL, and GCL thickness measured by OCT.

Macular OCT measurements were performed as defined by the Nomenclature of Optical Coherence Tomography (IN*OCT) panel [10]. The CMT was measured in 1st Early Treatment Diabetic Retinopathy Study (ETDRS) grid (the central grid) and defined as the retinal thickness between the internal limiting membrane (ILM) and the border between the outer segment of photoreceptors (12th layer) and the retinal pigment epithelium /Buch’s membrane (14th layer). The RT was the mean of all 9 ETDRS grids between the layers as the CMT. The RNFL thickness was the mean of all 9 ETDRS grids between the ILM and the border between the RNFL (3rd layer) and the GCL (4th layer). GCL thickness was the mean of all 9 ETDRS grids from the border between the 3rd and 4th layer and the border between the inner plexiform layer (5th layer) and the inner nuclear layer (6th layer).

After pupillary dilation, macular OCT was obtained using the DRI OCT Triton, Swept Source OCT (SS-OCT) (Topcon, Japan) and analyzed using IMAGE Net 6 (Topcon, Japan) within 0.5–1 h after pupillary dilation in a room lightened by artificial light. Most measurements were automated but manually corrected for obvious errors if the lines did not follow the right layers.

Patients were divided into four groups depending on their sarcoidosis phenotype: (a) sarcoidosis patients without ocular or CNS affection (Non-Ocular/Non-CNS), (b) patients with OS (Ocular), (c) patients with NS (CNS), and (d) patients with combined OS and NS (Ocular/CNS).

Information on organ involvement, sex, age, medical treatment, date of the first symptoms, and duration of illness were collected through medical journals and clinical examination of the patients. The ophthalmologic examination at the Department of Ophthalmology included best-corrected visual acuity (BCVA), slit-lamp analysis with gonioscopy, tonometry, and fundus examination.

The same clinician reviewed all the records to categorize patients. Likewise, the same two clinicians examined all patients. Participants’ age was the age at inclusion. Duration of sarcoidosis was defined as the time between biopsy verification of sarcoidosis and inclusion.

The BCVA was assessed using the Early Treatment Diabetic Retinopathy Study chart (Precision Vision, Woodstock, IL, USA) at four meters. Tonometry was done as a screening for raised intra-ocular pressure (IOP > 23 mmHg) and not a structured examination, as different devices were used.

Before dilation, a gonioscopy was performed to visualize peripheral anterior synechia. Afterward, potential active uveitis was examined in mydriasis with tropicamide 10 mg/ml and phenylephrine 10% and classified by the SUN criteria [22].

Data was collected and managed using REDCap electronic data capture tools hosted by Open Patient Data Explorative Network, Odense, Denmark.

Thestudywas approved by the Regional Ethics Committee of Southern Denmark (ID: S-20180153) and the Region of Southern Denmark's record of data processing activities (ID: 19/5546).

All participants signed an informed consent form before enrolment in the study.

Descriptive statistics were calculated for all parameters. Continuous data was presented as either mean and standard deviation (SD) or median with interquartile range (IQR). One-way-ANOVA or the Kruskal–Wallis test was used to compare groups depending on whether the data were normally distributed. Categorical data were reported as counts (n) and proportions (%) and compared using Fisher’s exact test.

The continuous variables, CMT, RT, RNFL, and GCL were analyzed using linear regression with cluster robust standard error, as every participant could contribute with two eyes, with sarcoidosis phenotype as categorical variables. The individual groups were compared to the Non-ocular/non-CNS group. Adjustments for age, sex, and immunosuppression did not improve the statistical model and were left out of the final model. Furthermore, we did a sub-analysis for patients who had been ill for less or more than five years.

A p-value below 0.05 was considered statistically significant. No correction for multiple analyses was made.

The datasets generated during and analyzed during the current study are available from the corresponding author upon reasonable request. Relevant authorities, e.g., the Danish Data Protection Agency, must approve the data requestors in adherence to GDPR regulations.