An apparatus and method for aiding in the detection of dementia, concussion, other neurologic conditions, retinal, and optic nerve conditions. The apparatus enables the diffusion coefficient of the tissue to be ascertained and studied by directing the light from a laser or other coherent light source at the patient's retina, optic nerve or choroid and measuring the fluctuations in the intensity of the back-scattered light caused by the movement of light scatterers in the tissue. By comparing the measurements to a normal database, or to the subject's previous measurement, in combination with an eye examination and OCT image/measurement the changes caused by the disease and the effectiveness of therapy can be ascertained. The disclosed apparatus allows the incident and detection optics to be attached to ophthalmic devices typically used in ophthalmologic care. Also, where both the incident laser fiber optic and the detection fiber optic are directly connected to goggles, one or more or all of the above-described mirrors may not be necessary, as both fiber optics are preferably directly directed into the eye.