Evaluation of the effect of subclinical hypothyroidism on retinal blood flow. OCT angiography study

Purpose: To evaluate retinal blood flow and retinal nerve fiber layer (RNFL) thickness in untreated subclinical hypothyroid patients by optical coherence tomography angiography (OCT-A). Methods: Forty-four eyes of 44 patients in the subclinical hypothyroidism group (SCHG) and 42 eyes of 42 healthy subjects in the control group (CG) were included in the study. Macular superficial retinal blood flow (SRBF), peripapillary RNFL thickness and optic nerve head cup to disk ratio (C/D) were measured and recorded by OCT angiography and compared between the patient and control groups. Correlation analysis between disease duration and SRBF and RNFL thickness was also performed. Results: Mean SRBF was 37.23 ± 2.11 in the SCH group and 38.45±1.20 in the control group. Mean SRBF was significantly lower in the SCH group (p=0.003). Mean Peripapillary RNFL thickness was 98.18±7.77 in the SCH group and 100.07 ± 7.71 in control group. Peripapillary RNFL thickness was not significantly different between groups (p=0.290). There was no significant difference in mean C/D between the groups (p=0.708). Correlation analysis showed a moderate negative correlation between duration of disease diagnosis and SRBF in the SCH group (p<0.001, r=-0.564). There was also a weak to moderate negative correlation between disease duration and RNFL thickness in SCH group (p=0.002, r=-0.489). Conclusions: A reduction in SRBF was observed in patients with subclinical hypothyroidism. Additionally, a negative correlation was identified between disease duration and RNFL thickness. Patients with subclinical hypothyroidism should be monitored for potential retinal vascular disease and the development of normotensive glaucoma.