A retrospective study on the prevalence of normal tension glaucoma among patients with Obstructive Sleep Apnea Syndrome

Abstract

Purpose To estimate the overall prevalence of normal tension glaucoma for a predominantly Chinese population who underwent sleep polysomnography for suspected obstructive sleep apnea in a specialty sleep clinic in a publicly-funded tertiary care hospital in Hong Kong. Methods This was a retrospective cross sectional study. In total, 1678 subjects underwent polysomnography (PSG) between 1st of January, 2005 and 31st of December, 2014. Their patient records were retrieved for data collection and analysis. The PSG apnea-hypopnea index (AHI) was considered as the diagnostic definition for obstructive sleep apnea while Anderson’s criteria was used for the diagnosis of normal tension glaucoma. Univariate analysis was conducted for potential risk factors, including patient age, gender, presence of hypertension, body mass index (BMI) and severity of OSAS. Results Amongst the 1678 subjects who underwent PSG during the study period. 426 of them were seen by at the ophthalmology specialty outpatient clinic of Queen Mary Hospital. The cumulative prevalence of NTG among them was 7.04%. Patients with severe OSAS had a higher prevalence of NTG than the normal population (7.69% versus 1.6%). Risk factors including older age, male gender, presence of hypertension and severity of OSAS had trends for higher prevalence of NTG but they were shown to be statistically insignificant. Conclusions Chinese patients with symptoms suggestive of obstructive sleep apnea syndrome are at significantly higher risk of developing normal tension glaucoma than the normal population. This suggests that screening measures for glaucoma in this asymptomatic population should be further investigated. However, the underlying mechanism linking the two conditions remains to be understood. Lastly, continuous positive airway Pressure (C-PAP) therapy was postulated to be a potential protective factor for NTG but further study is required to define this relationship.