Sleep Apnea and Cognitive Function in Subjects With Subjective or Mild Cognitive Impairment

Inclusion Criteria: * Aged 18 years and above * Clinical diagnosis of mild cognitive impairment (MCI) based on Petersen's criteria. The criteria include the following: (1) memory problems, (2) objective memory disorder, (3) absence of other cognitive disorders or repercussions on daily life, (4) normal general cognitive function and (5) absence of dementia OR, * Diagnosis of subjective cognitive impairment, based on the subject's own complaint of cognitive impairment but with an unremarkable assessment of the Hong Kong version of Montreal Cognitive Assessment scores * Able to speak and read Chinese * Adequate visual and auditory to perform a cognitive test Exclusion Criteria: * Diagnosed psychiatric illness with or without medication, e.g. major depressive disorder. * Other clear organic causes of cognitive impairment, e.g. old stroke, brain tumour, dementia with Lewy body, Parkinson's disease, normal pressure hydrocephalus, neurosyphilis, autoimmune encephalitis, substance abuse, history of alcohol abuse. * Diagnosis of major unstable illness or cancer on active treatment * Unable to perform Home Sleep Apnea Test * Those patients who require legal guardians