Jessica Tong1, Irene Yue1, Stuart Graham1, Claude Farah1,2, Clare Fraser1
Purpose: Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular disease; however the link with cerebral small-vessel disease is complex. The retina offers an in-vivo assessment of the cerebral microcirculation in OSA. Our study examined the relationship between retinal vascular parameters and OSA severity.
Method: Participants undergoing diagnostic polysomnography were prospectively recruited. OSA severity was defined by the apnea-hypopnea index (AHI): severe >30, moderate >15-30, mild 5-15, and normal <5. Minimum oxygen saturation (nadir SpO2) during sleep was recorded. Measures of retinal vascular diameter (CRVE: central retinal venular equivalent; AVR: arteriovenous ratio) were derived from fundus photographs (Vesselmap3, Jena/Germany). Amplitude of spontaneous retinal venular pulsations (SRVP) was also evaluated (Dynamic Vessel Analyser, Jena/Germany). Comparisons across groups were performed using multivariate linear regression analysis. A p-value<0.05 was considered significant.
Results: Of 97 participants recruited (61 males; mean age 56.9±13.5 years), there were 38 severe, 28 moderate, 20 mild OSA and 11 controls. Nadir SpO2 declined significantly with increasing AHI (r=-0.6, p<0.0005). Worsening nocturnal hypoxia was significantly associated with reduced AVR (p=0.04) and increased CRVE (p=0.02). OSA severity was significantly associated with attenuated SRVP (p<0.05). All results were adjusted for age and blood pressure.
Conclusion: Decreased AVR and enlarged CRVE have been associated with cerebrovascular ischaemia. Similarly, reduced SRVP may be secondary to compromised ocular blood flow. Our findings demonstrate retinal venular calibre is a precise indicator of microvascular perfusion in OSA, independent of age and blood pressure. The retina may elucidate the link between OSA and cerebral small-vessel disease.