Intrinsic signal detection of an evoked response with a low-cost scanning laser ophthalmoscope

A number of optical modalities exist for the imaging of retina structures, but no clinical devices exist for optically-based functional imaging of the retina. This paper reports on a device and on the image and signal processing techniques that were developed to perform functional image in mammalian retinas. These investigators first introduced a flood illuminated approach for functional imaging in 2002. That device required extensive measures, including an expensive thermal-electric cooled CCD camera, to minimize the noise in order to detect a signal with a magnitude of about 1.0 percent signal above the noise floor. The system designed and developed for this project uses low-cost optical and electronic components and low-cost lasers for illumination. The penalty paid is a device where noise reduction techniques must be employed to overcome the low signal-to-noise (SNR) in the resulting images. This paper reports on the successful application of a functional scanning laser ophthalmoscope for imaging the cat retina. Temporal and spatial averaging was used to extract a signal that is nominally three to five percent above the average signal.