Obsessive compulsive disorder (OCD) is a disease in which spontaneous remission is rare, causes significant impact on quality of life, and generally has a chronic course. Lifetime prevalence rates worldwide are estimated to be between 2 % and 3 % in developed countries (Kessler et al., 2011). About 50 % of those with OCD have the onset of symptoms in childhood and adolescence (Goodman et al., 2014). The exact cause of OCD is unknown, but it is likely multifactorial. Although the etiology of OCD is not fully known, there are various explanations for the disease. Many studies show that there are problems in the pathophysiology of OCD in the cortico-striato-thalamo-cortical circuits, which are responsible for reward-related processes, motor and response inhibition, and habit-based behavior (Van Den Heuvel et al., 2009; Fineberg et al., 2015).

In retinal physiology, the main neurotransmitter of photoreceptors responsible for vision is glutamate. Although neurotransmitters such as serotonin, dopamine, g-aminobutyric acid (GABA), glycine, acetylcholine, and taurine have also been detected in amacrine cells, which are interneurons in the retina, their exact functions are not yet fully known. Therefore, considering the functional disorder in the fronto-striato-thalamic circuits of OCD symptoms and the disorder in serotonin and dopamine neurotransmitters of OCD pathophysiology, it is thought that there may be some changes in the neuronal structure and physiology of the retina. Considered an extension of the brain, the retina is believed to be a critical piece in monitoring possible degeneration as part of the central nervous system (Zohar et al., 1999). Studies analyzing changes in neural networks in the retina in neurodegenerative diseases with optical coherence tomography (OCT), a non-invasive method developed for high-resolution cross-sectional imaging of biological tissues, have become more remarkable recently.

OCT was used to detect neuronal degeneration in neurological disorders including Alzheimer’s disease (Gunes et al., 2015), Parkinson disease (Sari et al., 2015), and Multiple Sclerosis (Hu et al., 2015). Similarly, OCT measurements have been made in many psychiatric diseases with known neurodegeneration, especially schizophrenia and mood disorders. (May-Yin Chu et al., 2012; Celik et al., 2016; Kalenderoglu, 2016a, 2016b). When the literature is examined, there are three studies that examine the relationship of peripapillary retinal nerve fiber layer thickness (RNFL) in OCD. These studies were both conducted with an adult age group (Polat et al., 2019). In one of the studies, no difference was detected between the patient and control groups. In the other study, a significant decrease was detected in the patient group (Ozen et al., 2019). According to the results of a recent study, peripapillary RNFL and ganglion cell complex thickness (GCC) measurements were found to be significantly lower (Onur et al., 2020). There is no study in the literature examining the relationship between pediatric age group and peripapillary RNFL.

The aim of this study is to compare the peripapillary RNFL levels, ganglion cell layer (GCL) volume, GCL thickness, GCC and central macular thickness (CMT) of OCD children and adolescents aged between 8–18 determined by the OCT method, compared with healthy controls. Additionally, it will be investigated whether there is a relationship between disease severity and RNFL measurements.