HKUMed and CityU Scientists Discover Noninvasive Eye Stimulation for Depression and Dementia

Major depression is the most common and serious psychiatric disorder in the world. Recently, the World Health Organization reported that the COVID-19 pandemic has triggered a massive increase in the number of people suffering from anxiety and depression. Although treatments are available for depression, about a quarter of patients do not respond adequately to these treatments.

Assistant Professor Dr. Lim Lee Wei, lead researcher and also former researcher from Singapore Lee Kuan Yew, reported in 2015 that deep brain stimulation of the prefrontal cortex in animal brains could improve memory function and relieve depressive symptoms. These therapeutic effects have been attributed to the growth of brain cells in the hippocampus, a region of the brain known to be involved in learning and memory functions. However, this technique also known as deep brain stimulation is invasive and requires surgery to implant electrodes into the brain, which can lead to side effects such as infections and post-operative complications.

A team of hong kong researchers led by Dr. Lim Lee Weidoctor Leanne Chan Lai Hangand teacher Chan Ying-Shing sought alternative ways to treat neuropsychiatric illnesses. They found that noninvasive stimulation of the corneal surface of the eye, which activates brain pathways, resulted in remarkable antidepressant effects and also reduced stress hormones in an animal model of depression. This technique called transcorneal electrical stimulation also induces the expression of genes involved in the development and growth of brain cells in the hippocampus.

In related experiments, Yu Wing Shan and other research members investigated whether this approach could also be used to treat Alzheimer’s disease, a common type of dementia with no definitive cure. They found that this noninvasive stimulation in mice significantly improved memory performance and reduced beta-amyloid deposits in the hippocampus, which is one of the hallmarks of Alzheimer’s disease.

Associate Professor Dr. Leanne ChanCityU’s principal investigator and an expert in electrical stimulation of visual and non-visual brain targets, described the research: “Transcorneal Electrical Stimulation is a non-invasive method originally developed to treat eye diseases, and it would be a major scientific discovery breakthrough if it could be applied to treat neuropsychiatric diseases.

“These research results pave the way for new therapeutic opportunities to develop a new treatment for patients with treatment-resistant depression and dementia, however, clinical trials should be conducted to validate efficacy and safety,” said points out the teacher Chan Ying-Shing of HKUMed and editor of IBRO Neuroscience Reports. The application of this non-invasive eye stimulation brings new hope to people suffering from depression and dementia.

These important findings were recently published in brain stimulation and Annals of the New York Academy of Sciences. Yu Wing Shanwho was the principal investigator of these studies, and a recipient of the prestigious Hong Kong PhD Fellowship, awarded by the Hong Kong Research Grants Council to the HKUMed Neuromodulation Laboratory (, in collaboration with CityU of the Neural Interface Research Laboratory (


WS Yu, ACK Tse, L Guan, JLY Chiu, SZK Tan, S Khairuddin, SK Agadagba, ACY Lo, ML Fung, YS Chan, LLH Chan, LW Lim. (2022) Antidepressant-like behaviors by transcorneal electrical stimulation in rat models. brain stimulation. 15(3):843-856.

WS Yu, L Aquili, KH Wong, ACY Lo, LLH Chan, YS Chan, LW Lim. (2022) Transcorneal Electrical Stimulation Improves Cognitive Functions in Aged and 5xFAD Mouse Models. Ann. NY Acad. Science. DOI: 10.1111/nyas.14850.

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