全球人口老化的問題嚴重，世界衛生組織（WHO）預測2020年中國60歲以上老年人口所占的比例將由2016年的10.5%上升到20%。導致人口老化的關鍵原因主要是平均期望?命延長和生育率下降。而年齡與認知障礙症的患病率呈正相關。國際失智症協會提出2017年認知障礙症患者接近5000萬人，未來將有更多人患上認知障礙症。許多研究顯示視力損害與老年人的認知障礙症有關，並表示視力損害能預測認知功能的下降。全球50歲以上的老年人大約有65%患有視力損害，根據WHO統計，全球致盲疾病頭三位包括年齡相關性黃斑變性、青光眼和白內障，它們都跟認知障礙症中的阿茲海默氏症有密切關係。關於認知功能下降和視力損害之間關係的假說主要有4種，而信息降格假說比較多人認同。除了眼疾，光線跟認知功能也有相關性。當中的關鍵可能是存在於視網膜神經節細胞的黑視蛋白，它感光後會觸發並激活大腦關於警覺性和執行功能的相關區域。另一方面，有些學者希望從中獲得預防和治療認知障礙症的線索，但研究比較少，至令還沒有定論。
Population aging is a severe global problem. In China, WHO predicts that the proportion of elderly people over the age of 60 will increase from 10.5% in 2016 to 20% in 2020. The main causes of population aging are the extension of average expected lifespan and the decline in fertility. Age is positively correlated with the prevalence of the major neurocognitive disorder. Alzheimer's Disease International has proposed nearly 50 million people with the major neurocognitive disorder in 2017, and more people will suffer from the major neurocognitive disorder in the future. Many studies have shown that visual impairment is associated with the major neurocognitive disorder in the elderly, and visual impairment can predict a decline in cognitive function. About 65% of people who are over 50 suffer from visual impairment in the world. According to WHO, the top three global blinding diseases include age-related macular degeneration, glaucoma and cataract, and those diseases are also related to Alzheimer's Disease which is one of the major neurocognitive disorders. There are 4 kinds of hypothesizes about the relationship between cognitive decline and visual impairment, and the information degradation hypothesis is more acceptable. In addition to eye diseases, light is also related to cognitive function. The key role may be the melanopsin, which is a protein present in retinal ganglion cells, it can trigger and activate the brain's relevant areas of alertness and executive function. On the other hand, some scholars hope to find out clues to prevent and treat cognitive disorders, but there is still no conclusion about this.
