Researchers are exploring various methods to detect Alzheimer's disease before symptoms appear, with some studies suggesting that changes may occur decades in advance. Blood tests, retinal photographs, and even nasal detection are being investigated as potential tools for predicting the risk of Alzheimer's, with some studies indicating that a blood test may be able to predict risk up to 25 years before symptoms begin. The exact timing and methods of early detection are still being studied, but multiple approaches show promise.