Blood And Tears in Alzheimer's Disease

This study explores whether a simple blood test and a tear sample can help diagnose Alzheimer's disease and other brain diseases as accurately as the current spinal fluid test. The goal is to find easier, less invasive ways to detect these conditions early. **You may be eligible if:** - You are a legal adult - You are having or have already had a spinal fluid (lumbar puncture) sample taken - You have been diagnosed with Alzheimer's disease, Lewy body dementia, frontotemporal dementia, vascular dementia, or normal pressure hydrocephalus — OR you are a healthy person with no neurological disease who is also undergoing a lumbar puncture **You may NOT be eligible if:** - You are not having a lumbar puncture - Your doctor considers you medically unfit to take part Talk to your doctor to see if this trial is right for you.