An method for detection of β-amyloid in aqueous humor, lens, and retina of eye or the deposit of the combination of αβ-crystallin and β-amyloid in lens is provided. A light is emitted to a testing area in the eye. The light frequency is selected according to an absorption spectrum of the test substance, and the frequency is equal or close to a resonant excitation frequency of one of the electronic molecular energy levels of the substance, so as to excite the substance to generate resonance-enhanced Raman effect or pre-resonance Raman effect to form a detection spectrum. The concentration of the substance could be estimated by a peak intensity of the detection spectrum.
