Decreased Optic Nerve Head Perfusion in Patients with Normal Tension Glaucoma and Obstructive Sleep Apnoea

Background: To compare optic nerve head (ONH) perfusion using laser speckle flowgraphy (LSFG) (Softcare Co., Ltd., Fukuoka, Japan) in sitting and supine positions between eyes with normal tension glaucoma and obstructive sleep apnoea (NTG-OSA) versus normal controls. Methods: Intraocular pressure (IOP), body mass index (BMI), and LSFG measurements (mean blur rate (MBR), blowout score (BOS), and blowout time (BOT)) were taken in sitting and supine positions. MBR is a quantitative index of blood cell velocity, a proxy of tissue blood flow. BOS is the blood volume maintained within a vessel during each heartbeat. BOT is the time within one heartbeat that maintains >½ average MBR. A higher BOT implies that blood flow is maintained at a sufficiently high level for a longer duration during each heartbeat for tissue perfusion. Results: 45 NTG-OSA and 29 normal eyes were recruited. The MBR of all areas, vascular areas, and tissue areas were significantly lower in the NTG-OSA group compared to the normal controls in both sitting and supine positions (all p<0.05). When changing from sitting to supine, normal eyes had significantly greater increase in BOS compared to the increase in NTG-OSA eyes (p<0.05), but only NTG-OSA eyes had significant increases in BOT (p<0.05). Conclusion: NTG-OSA eyes have significantly lower ONH perfusion, as measured by decreased MBR on LSFG, in both sitting and supine positions. The prolonged maintenance of high ONH perfusion with a change in body posture, represented by an increase in BOS may represent altered microvascular autoregulation in patients with NTG-OSA.