Evaluation of optic nerve subarachnoid space in primary open angle glaucoma using ultrasound examination

OBJECTIVES: To measure Optic Nerve Subarachnoid Space (ONSAS) in patients with primary open-angle glaucoma (POAG) and controls using A-scan ultrasound and to evaluate the measurement of the ONSAS in relation to age patient and OCT parameters. METHODS: This retrospective study included 53 consecutive eyes of 27 patients with POAG and 64 normal eyes of 32 controls. Both glaucomatous and control groups were divided into 2 subgroups according to age: <60 age (glaucomatous and control group 1) and 61-90 age (glaucomatous and control group 2). RESULTS: The ONSAS was significantly lower in all glaucomatous eyes (3.54 ± 0.38) versus normal eyes (3.87 ± 0.32) (p = 0.001). Significant reduction of ONSAS was showed in control group 2 (3.63 mm ± 0.37) compared to control group 1 (3.87 mm ± 0.32) (p = 0.014) and between glaucoma group 1 (3.54 mm ± 0.38) and control group 1 (p = 0.001). While no significant differences were observed between glaucomatous group 2 (3.48 mm ± 0.41) and control group 2 (p = 0.17) and between glaucoma group 1 and glaucoma group 2 (p = 0.609). Lastly, the ONSAS was not significantly associated with GCC and RNFL parameters except for Focal Loss Volume (FLV), Superior RNFL and ONSAS in glaucoma group 1 and for FLV and ONSAS in all glaucomatous group. CONCLUSION: Standardized A-scan ultrasound is a non invasive imaging technique with which it is possible to monitor ONSAS changes in glaucomatous patients. The reduction of ONSAS confirm the importance of the lower orbital CSFP as further risk factor in the progression of glaucoma disease.